Study on acoustic-electric-heat effect of coal and rock failure processes under uniaxial compression

NASA Astrophysics Data System (ADS)

Li, Zhong-Hui; Lou, Quan; Wang, En-Yuan; Liu, Shuai-Jie; Niu, Yue

2018-02-01

In recent years, coal and rock dynamic disasters are becoming more and more severe, which seriously threatens the safety of coal mining. It is necessary to carry out an depth study on the various geophysical precursor information in the process of coal and rock failure. In this paper, with the established acoustic-electric-heat multi-parameter experimental system of coal and rock, the acoustic emission (AE), surface potential and thermal infrared radiation (TIR) signals were tested and analyzed in the failure processes of coal and rock under the uniaxial compression. The results show that: (1) AE, surface potential and TIR have different response characteristics to the failure process of the sample. AE and surface potential signals have the obvious responses to the occurrence, extension and coalescence of cracks. The abnormal TIR signals occur at the peak and valley points of the TIR temperature curve, and are coincident with the abnormities of AE and surface potential to a certain extent. (2) The damage precursor points and the critical precursor points were defined to analyze the precursor characteristics reflected by AE, surface potential and TIR signals, and the different signals have the different precursor characteristics. (3) The increment of the maximum TIR temperature after the main rupture of the sample is significantly higher than that of the average TIR temperature. Compared with the maximum TIR temperature, the average TIR temperature has significant hysteresis in reaching the first peak value after the main rapture. (4) The TIR temperature contour plots at different times well show the evolution process of the surface temperature field of the sample, and indicate that the sample failure originates from the local destruction.

True Triaxial Strength and Failure Modes of Cubic Rock Specimens with Unloading the Minor Principal Stress

NASA Astrophysics Data System (ADS)

Li, Xibing; Du, Kun; Li, Diyuan

2015-11-01

True triaxial tests have been carried out on granite, sandstone and cement mortar using cubic specimens with the process of unloading the minor principal stress. The strengths and failure modes of the three rock materials are studied in the processes of unloading σ 3 and loading σ 1 by the newly developed true triaxial test system under different σ 2, aiming to study the mechanical responses of the rock in underground excavation at depth. It shows that the rock strength increases with the raising of the intermediate principal stress σ 2 when σ 3 is unloaded to zero. The true triaxial strength criterion by the power-law relationship can be used to fit the testing data. The "best-fitting" material parameters A and n ( A > 1.4 and n < 1.0) are almost located in the same range as expected by Al-Ajmi and Zimmerman (Int J Rock Mech Min Sci 563 42(3):431-439, 2005). It indicates that the end effect caused by the height-to-width ratio of the cubic specimens will not significantly affect the testing results under true triaxial tests. Both the strength and failure modes of cubic rock specimens under true triaxial unloading condition are affected by the intermediate principal stress. When σ 2 increases to a critical value for the strong and hard rocks (R4, R5 and R6), the rock failure mode may change from shear to slabbing. However, for medium strong and weak rocks (R3 and R2), even with a relatively high intermediate principal stress, they tend to fail in shear after a large amount of plastic deformation. The maximum extension strain criterion Stacey (Int J Rock Mech Min Sci Geomech Abstr 651 18(6):469-474, 1981) can be used to explain the change of failure mode from shear to slabbing for strong and hard rocks under true triaxial unloading test condition.

Limits on rock strength under high confinement

NASA Astrophysics Data System (ADS)

Renshaw, Carl E.; Schulson, Erland M.

2007-06-01

Understanding of deep earthquake source mechanisms requires knowledge of failure processes active under high confinement. Under low confinement the compressive strength of rock is well known to be limited by frictional sliding along stress-concentrating flaws. Under higher confinement strength is usually assumed limited by power-law creep associated with the movement of dislocations. In a review of existing experimental data, we find that when the confinement is high enough to suppress frictional sliding, rock strength increases as a power-law function only up to a critical normalized strain rate. Within the regime where frictional sliding is suppressed and the normalized strain rate is below the critical rate, both globally distributed ductile flow and localized brittle-like failure are observed. When frictional sliding is suppressed and the normalized strain rate is above the critical rate, failure is always localized in a brittle-like manner at a stress that is independent of the degree of confinement. Within the high-confinement, high-strain rate regime, the similarity in normalized failure strengths across a variety of rock types and minerals precludes both transformational faulting and dehydration embrittlement as strength-limiting mechanisms. The magnitude of the normalized failure strength corresponding to the transition to the high-confinement, high-strain rate regime and the observed weak dependence of failure strength on strain rate within this regime are consistent with a localized Peierls-type strength-limiting mechanism. At the highest strain rates the normalized strengths approach the theoretical limit for crystalline materials. Near-theoretical strengths have previously been observed only in nano- and micro-scale regions of materials that are effectively defect-free. Results are summarized in a new deformation mechanism map revealing that when confinement and strain rate are sufficient, strengths approaching the theoretical limit can be achieved in cm-scale sized samples of rocks rich in defects. Thus, non-frictional failure processes must be considered when interpreting rock deformation data collected under high confinement and low temperature. Further, even at higher temperatures the load-bearing ability of crustal rocks under high confinement may not be limited by a frictional process under typical geologic strain rates.

A quantitative analysis of rock cliff erosion environments

NASA Astrophysics Data System (ADS)

Lim, M.; Rosser, N.; Petley, D. N.; Norman, E. C.; Barlow, J.

2009-12-01

The spatial patterns and temporal sequencing of failures from coastal rock cliffs are complex and typically generate weak correlations with environmental variables such as tidal inundation, wave energy, wind and rain. Consequently, understanding of rock cliff behaviour, its response to predicted changes in environmental forcing and, more specifically, the interaction between marine and climatic factors in influencing failure processes has remained limited. This work presents the results from the first attempt to characterise and quantify the conditions on coastal cliffs that lead to accelerated rates of material detachment. The rate of change in an 80 m high section of coastal rock cliffs has been surveyed annually with high-resolution terrestrial laser scanning (TLS). The rockfall data have been analysed according to a simplified source geology that exhibit distinct magnitude-frequency distributions relating to the dominance of particular failure types. An integrated network of sensors and instrumentation designed to reflect the lithological control on failure has been installed to examine both the distinction between prevailing conditions and those affecting the local cliff environment and the physical response of different rock types to micro-climatic processes. The monitoring system records near-surface rock strain, temperature, moisture and micro-seismic displacement in addition to air temperature, humidity, radiation, precipitation, water-level and three-dimensional wind characteristics. A characteristic environmental signal, unique to the cliff face material, has been identified that differs substantially from that experienced by the surrounding area; suggesting that established methods of meteorological and tidal data collection are insufficient and inappropriate to represent erosive processes. The interaction between thermo- and hydro-dynamics of the cliff environment and the physical response of the rock highlights the composite environmental effects acting on the rock mass and provides a new interpretation on the dominant controls on the behaviour of coastal rock cliffs that challenges the almost universal application of undercutting and cantilever collapse as the primary driver of rock cliff erosion.

Rock mass characterisation and stability analyses of excavated slopes

NASA Astrophysics Data System (ADS)

Zangerl, Christian; Lechner, Heidrun

2016-04-01

Excavated slopes in fractured rock masses are frequently designed for open pit mining, quarries, buildings, highways, railway lines, and canals. These slopes can reach heights of several hundreds of metres and in cases concerning open pit mines slopes larger than 1000 m are not uncommon. Given that deep-seated slope failures can cause large damage or even loss of life, the slope design needs to incorporate sufficient stability. Thus, slope design methods based on comprehensive approaches need to be applied. Excavation changes slope angle, groundwater flow, and blasting increases the degree of rock mass fracturing as well as rock mass disturbance. As such, excavation leads to considerable stress changes in the slopes. Generally, slope design rely on the concept of factor of safety (FOS), often a requirement by international or national standards. A limitation of the factor of safety is that time dependent failure processes, stress-strain relationships, and the impact of rock mass strain and displacement are not considered. Usually, there is a difficulty to estimate the strength of the rock mass, which in turn is controlled by an interaction of intact rock and discontinuity strength. In addition, knowledge about in-situ stresses for the failure criterion is essential. Thus, the estimation of the state of stress of the slope and the strength parameters of the rock mass is still challenging. Given that, large-scale in-situ testing is difficult and costly, back-calculations of case studies in similar rock types or rock mass classification systems are usually the methods of choice. Concerning back-calculations, often a detailed and standardised documentation is missing, and a direct applicability to new projects is not always given. Concerning rock mass classification systems, it is difficult to consider rock mass anisotropy and thus the empirical estimation of the strength properties possesses high uncertainty. In the framework of this study an approach based on numerical discrete element modelling (DEM) in combination with limit-equilibrium (LE) methods are presented. The advantage of DEM methods is that failure and displacement of discontinuities and the intact rock for the investigation of failure mechanisms and slope deformations are considered. Furthermore, DEM methods have its strength when rock masses are highly anisotropic and slope failure is structurally controlled. Herein DEM methods are applied to model potential failure geometries, which in turn serve as basis for further investigations by limit-equilibrium methods. LE-methods are used to determine the factor of safety for the pre-defined failure geometries where a sliding mechanism with a discrete and pre-defined basal shear zone is the most likely kinematical failure mode. In this study a parameter variation was performed to find the most reliable FOS based on field estimated strength parameters and the critical strength parameter where a FOS is equal to one (i.e. the lower limit for the parameters). Furthermore, the sensitivity of the shear strength parameters is studied, which enables plausibility checks with field measurements and back-calculated values. The combined approach can help to gain a better insight into failure processes and deformation mechanisms and facilitate to perform a parameter-variation study at a reasonable time frame.

Folded fabric tunes rock deformation and failure mode in the upper crust.

PubMed

Agliardi, F; Dobbs, M R; Zanchetta, S; Vinciguerra, S

2017-11-10

The micro-mechanisms of brittle failure affect the bulk mechanical behaviour and permeability of crustal rocks. In low-porosity crystalline rocks, these mechanisms are related to mineralogy and fabric anisotropy, while confining pressure, temperature and strain rates regulate the transition from brittle to ductile behaviour. However, the effects of folded anisotropic fabrics, widespread in orogenic settings, on the mechanical behaviour of crustal rocks are largely unknown. Here we explore the deformation and failure behaviour of a representative folded gneiss, by combining the results of triaxial deformation experiments carried out while monitoring microseismicity with microstructural and damage proxies analyses. We show that folded crystalline rocks in upper crustal conditions exhibit dramatic strength heterogeneity and contrasting failure modes at identical confining pressure and room temperature, depending on the geometrical relationships between stress and two different anisotropies associated to the folded rock fabric. These anisotropies modulate the competition among quartz- and mica-dominated microscopic damage processes, resulting in transitional brittle to semi-brittle modes under P and T much lower than expected. This has significant implications on scales relevant to seismicity, energy resources, engineering applications and geohazards.

Geophysical Signatures of Shear-Induced Damage and Frictional Processes on Rock Joints

NASA Astrophysics Data System (ADS)

Hedayat, Ahmadreza; Haeri, Hadi; Hinton, John; Masoumi, Hossein; Spagnoli, Giovanni

2018-02-01

In this study, ultrasonic waves recorded during direct shear experiments on rock joints were employed to investigate the shear failure processes. Three types of wave attributes were systematically observed prior to the shear failure of the rock joints: (a) maximum in the amplitude of the transmitted wave, (b) maximum in the dominant frequency of the transmitted wave, and (c) maximum in the velocity of the wave. Different processes occurring during both frictional sliding and stick-slip oscillations were identified in this study: (a) interseismic phase and (b) preseismic phase. The interseismic phase is associated with elastic loading, very small local slip rate, and increasing ultrasonic transmission along the contact surfaces. The rock joint is considered locked, and the increase in ultrasonic transmission represents an increase in the real (true) area of contact because of interlocking and contact aging. The start of the preseismic phase is marked by the onset of precursors for different regions of the rock joint. Following the interseismic and preseismic phases, coseismic phase occurs. The coseismic phase begins with the reduction in the applied shear stress and is associated with an abrupt increase in the local slip rate. The reductions in transmitted amplitude, wave velocity, and dominant frequency all indicate the preseismic phase when the asperity contacts begin to fail before macroscopic frictional sliding. The observation of the preseismic phase in both the loading phase leading to stable sliding and stick-slip failure modes suggests that microphysical processes of fault weakening may share key features for these two failure modes.

A new method to estimate location and slip of simulated rock failure events

NASA Astrophysics Data System (ADS)

Heinze, Thomas; Galvan, Boris; Miller, Stephen Andrew

2015-05-01

At the laboratory scale, identifying and locating acoustic emissions (AEs) is a common method for short term prediction of failure in geomaterials. Above average AE typically precedes the failure process and is easily measured. At larger scales, increase in micro-seismic activity sometimes precedes large earthquakes (e.g. Tohoku, L'Aquilla, oceanic transforms), and can be used to assess seismic risk. The goal of this work is to develop a methodology and numerical algorithms for extracting a measurable quantity analogous to AE arising from the solution of equations governing rock deformation. Since there is no physical property to quantify AE derivable from the governing equations, an appropriate rock-mechanical analog needs to be found. In this work, we identify a general behavior of the AE generation process preceding rock failure. This behavior includes arbitrary localization of low magnitude events during pre-failure stage, followed by increase in number and amplitude, and finally localization around the incipient failure plane during macroscopic failure. We propose deviatoric strain rate as the numerical analog that mimics this behavior, and develop two different algorithms designed to detect rapid increases in deviatoric strain using moving averages. The numerical model solves a fully poro-elasto-plastic continuum model and is coupled to a two-phase flow model. We test our model by comparing simulation results with experimental data of drained compression and of fluid injection experiments. We find for both cases that occurrence and amplitude of our AE analog mimic the observed general behavior of the AE generation process. Our technique can be extended to modeling at the field scale, possibly providing a mechanistic basis for seismic hazard assessment from seismicity that occasionally precedes large earthquakes.

Reconstruction of multistage massive rock slope failure: Polymethodical approach in Lake Oeschinen (CH)

NASA Astrophysics Data System (ADS)

Knapp, Sibylle; Gilli, Adrian; Anselmetti, Flavio S.; Hajdas, Irka

2016-04-01

Lateglacial and Holocene rock-slope failures occur often as multistage failures where paraglacial adjustment and stress adaptation are hypothesised to control stages of detachment. However, we have only limited datasets to reconstruct detailed stages of large multistage rock-slope failures, and still aim at improving our models in terms of geohazard assessment. Here we use lake sediments, well-established for paleoclimate and paleoseismological reconstruction, with a focus on the reconstruction of rock-slope failures. We present a unique inventory from Lake Oeschinen (Bernese Alps, Switzerland) covering about 2.4 kyrs of rock-slope failure history. The lake sediments have been analysed using sediment-core analysis, radiocarbon dating and seismic-to-core and core-to-core correlations, and these were linked to historical and meteorological records. The results imply that the lake is significantly younger than the ~9 kyrs old Kandersteg rock avalanche (Tinner et al., 2005) and shows multiple rock-slope failures, two of which could be C14-dated. Several events detached from the same area potentially initiated by prehistoric earthquakes (Monecke et al., 2006) and later from stress relaxation processes. The data imply unexpected short recurrence rates that can be related to certain detachment scarps and also help to understand the generation of a historical lake-outburst flood. Here we show how polymethodical analysis of lake sediments can help to decipher massive multistage rock-slope failure. References Monecke, K., Anselmetti, F.S., Becker, A., Schnellmann, M., Sturm, M., Giardini, D., 2006. Earthquake-induced deformation structures in lake deposits: A Late Pleistocene to Holocene paleoseismic record for Central Switzerland. Eclogae Geologicae Helvetiae, 99(3), 343-362. Tinner, W., Kaltenrieder, P., Soom, M., Zwahlen, P., Schmidhalter, M., Boschetti, A., Schlüchter, C., 2005. Der nacheiszeitliche Bergsturz im Kandertal (Schweiz): Alter und Auswirkungen auf die damalige Umwelt. Eclogae Geologicae Helvetiae, 98(1), 83-95.

Influence of Unloading Rate on the Strainburst Characteristics of Beishan Granite Under True-Triaxial Unloading Conditions

NASA Astrophysics Data System (ADS)

Zhao, X. G.; Wang, J.; Cai, M.; Cheng, C.; Ma, L. K.; Su, R.; Zhao, F.; Li, D. J.

2014-03-01

Rockburst is a sudden and violent failure of rocks and it often occurs in hard rocks in highly stressed ground. Strainburst is classified as one type of rockburst and it often occurs in rocks near or at the excavation boundary. Deep insight into the strainburst phenomenon is essential for safe underground construction at depth. In this paper, an experimental laboratory study on the strainburst behavior of Beishan granite is presented. Based on in-situ stress measurement data from the Beishan area in China, a series of tests under different unloading rates were performed to investigate the strainburst process using a true-triaxial strainburst test system which was equipped with an acoustic emission (AE) monitoring system. In addition, a high-speed video camera was used to record and visualize the initiation and ejection of rock fragments as well as the sudden dynamic failure (strainburst) of the test samples. AE characteristics associated with the cumulative energy and frequency-amplitude distributions were analyzed. Characteristics of the microscopic structure of a fragment generated from one test were observed using a scanning electron microscope. The experimental results indicate that the degree of violence during failure and the associated AE energy release in the strainburst process are dependent on the unloading rate. When the unloading rate is high, the rock is prone to strainburst. On the other hand, as the unloading rate decreases, the failure mode changes from strainburst to spalling. In addition, the cumulative AE energy is not sensitive to unloading rates greater than 0.05 MPa/s. When the unloading rate is less than 0.05 MPa/s, the cumulative AE energy shows a marked decreasing trend during rock failure.

A Study of Specific Fracture Energy at Percussion Drilling

NASA Astrophysics Data System (ADS)

A, Shadrina; T, Kabanova; V, Krets; L, Saruev

2014-08-01

The paper presents experimental studies of rock failure provided by percussion drilling. Quantification and qualitative analysis were carried out to estimate critical values of rock failure depending on the hammer pre-impact velocity, types of drill bits and cylindrical hammer parameters (weight, length, diameter), and turn angle of a drill bit. Obtained data in this work were compared with obtained results by other researchers. The particle-size distribution in granite-cutting sludge was analyzed in this paper. Statistical approach (Spearmen's rank-order correlation, multiple regression analysis with dummy variables, Kruskal-Wallis nonparametric test) was used to analyze the drilling process. Experimental data will be useful for specialists engaged in simulation and illustration of rock failure.

Large Deformation Characteristics and Reinforcement Measures for a Rock Pillar in the Houziyan Underground Powerhouse

NASA Astrophysics Data System (ADS)

Xiao, Xin-hong; Xiao, Pei-wei; Dai, Feng; Li, Hai-bo; Zhang, Xue-bin; Zhou, Jia-wen

2018-02-01

The underground powerhouse of the Houziyan Hydropower Station is under the conditions of high geo-stress and a low strength/stress ratio, which leads to significant rock deformation and failures, especially for rock pillars due to bidirectional unloading during the excavation process. Damages occurred in thinner rock pillars after excavation due to unloading and stress concentration, which will reduce the surrounding rock integrity and threaten the safety of the underground powerhouse. By using field investigations and multi-source monitoring data, the deformation and failure characteristics of a rock pillar are analyzed from the tempo-spatial distribution features. These results indicate that significant deformation occurred in the rock pillar when the powerhouse was excavated to the fourth layer, and the maximum displacement reached 107.57 mm, which occurred on the main transformer chamber upstream sidewall at an elevation of 1721.20 m. The rock deformation surrounding the rock pillar is closely related to the excavation process and has significant time-related characteristics. To control large deformation of the rock pillar, thru-anchor cables were used to reinforce the rock pillar to ensure the stability of the powerhouse. The rock deformation surrounding the rock pillar decreases gradually and forms a convergent trend after reinforcement measures are installed based on the analysis of the temporal characteristics and the rock pillar deformation rate.

Tectonic constraints on a deep-seated rock slide in weathered crystalline rocks

NASA Astrophysics Data System (ADS)

Borrelli, Luigi; Gullà, Giovanni

2017-08-01

Deep-seated rock slides (DSRSs), recognised as one of the most important mass wasting processes worldwide, involve large areas and cause several consequences in terms of environmental and economic damage; they result from a complex of controlling features and processes. DSRSs are common in Calabria (southern Italy) where the complex geo-structural setting plays a key role in controlling the geometry of the failure surface and its development. This paper describes an integrated multi-disciplinary approach to investigate a DSRS in Palaeozoic high-grade metamorphic rocks of the Sila Massif; it focuses on the definition of the internal structure and the predisposing factors of the Serra di Buda landslide near the town of Acri, which is a paradigm for numerous landslides in this area. An integrated interdisciplinary study based on geological, structural, and geomorphological investigations-including field observations of weathering grade of rocks, minero-petrographic characterisations, geotechnical investigations and, in particular, fifteen years of displacement monitoring-is presented. Stereoscopic analysis of aerial photographs and field observations indicate that the Serra di Buda landslide consists of two distinct compounded bodies: (i) an older and dormant body ( 7 ha) and (ii) a more recent and active body ( 13 ha) that overlies the previous one. The active landslide shows movement linked to a deep-seated translational rock slide (block slide); the velocity scale ranges from slow (1.6 m/year during paroxysmal stages) to extremely slow (< 16 mm/year during stable creep stages). The geological structures and rock weathering have played a key role in the landslide's initiation and further development. Steep slope angles, rugged topography, river deepening and erosion at the toe of the slope are also responsible for the formation of this landslide. In particular, the landslide shows a strongly tectonic constraint: the flanks are bounded by high-angle faults, and the main basal failure surface developed inside an E-W southward-dipping thrust fault zone. The entire active rock mass (total volume of approximately 6 Mm3) slid at one time on a failure surface that dipped < 27°, and the maximum depth, as determined by inclinometer measurements, was approximately 58 m. Petrographic and mineralogical analyses suggest that the rocks in the thrust zones, where the failure surfaces develop, are highly affected by weathering processes that significantly reduce the rock strength and facilitate the extensive failure of the Serra di Buda landslide. Finally, the landslide's internal structure, according to geotechnical investigations and displacement monitoring, is proposed. The proposed approach and the obtained results can be generalised to typify other deep landslides in similar geological settings.

Rock-slope failure activity and geological crises in western Norway

NASA Astrophysics Data System (ADS)

Hilger, Paula; Hermanns, Reginald L.; Myhra, Kristin S.; Gosse, John C.; Ivy-Ochs, Susan; Etzelmüller, Bernd

2017-04-01

In Norway a compilation of terrestrial cosmogenic nuclide (TCN) ages of rock-avalanche deposits suggests a close link of rock-slope failures related to deglaciation. Although ages spread over several thousand years at the end of the Late Pleistocene, 50% of all documented events occurred within 1000 years after deglaciation. It is therefore likely that debuttressing triggered most of the events. The same data set suggests that 25% of the events occurred during a period stretching until the Holocene thermal maximum (HTM). These events might be interpreted as possible reactions to additional factors such as the thawing of high-altitude permafrost. An example of a geological crisis following deglaciation and before the HTM are seven lobate rock-avalanche deposits mapped under the slope of the Vora mountain (1450 m asl.) in the Nordfjord area of western Norway. Three events of this rock-slope failure cluster date within a short time period of 2000 years, where modelling studies indicate that high-altitude permafrost was present. After the HTM rock-slope failures are distributed temporally and spatially rather evenly throughout the Holocene and western Norway. But there are two independent local clusters with frequent rock slides during a short time span. (1) At the active Mannen rock-slope instability several rock-avalanche and rockslide deposits were mapped on the valley bottom. Stratigraphic relations combined with TCN dating suggest that at least one event occurred when the valley bottom was below the marine limit. TCN ages of further four lobes cluster around 5.2 ka BP, which does not coincide with any other rock-avalanche occurrence in the region. The top of the north facing 1295 m high unstable slope concurs with the currently estimated permafrost boundary. Preliminary TCN ages of the sliding surface indicate that larger parts of the mountain did not become active until the climate maximum. It is likely that due to structural complexity not allowing for any easy kinematic failure process, it required several thousand years of rock-slope deformation prior to the multiple failures. (2) The youngest independent rock-avalanche cluster is historic with 5 rock avalanches sourcing from Ramnefjellet in 1905, 1936 (three events), and 1950 entering into Loen lake in western Norway. Subsequent displacement waves killed 61 people in 1905 and 73 people due to the first failure in 1936. The back scarp does not exceed 850 m elevation and lies hence below the present day and Little Ice Age permafrost limit. It is therefore unlikely that permafrost dynamics contribute to this sequence of rock-slope failures. Local clusters or a geological crisis by rock-slope failures seems to be related to different main factors, such as glacial debutressing, influence of ground thermal regime changes (Mannen) and probably more disconnected to major climate variability (Loen). For an integrated risk management it is therefore important to understand that large rock-slope failures do not necessarily have to occur in single events but can occur over several decades or centuries and thus complicate severely land use management after catastrophic events.

Dynamic Response and Failure Mechanism of Brittle Rocks Under Combined Compression-Shear Loading Experiments

NASA Astrophysics Data System (ADS)

Xu, Yuan; Dai, Feng

2018-03-01

A novel method is developed for characterizing the mechanical response and failure mechanism of brittle rocks under dynamic compression-shear loading: an inclined cylinder specimen using a modified split Hopkinson pressure bar (SHPB) system. With the specimen axis inclining to the loading direction of SHPB, a shear component can be introduced into the specimen. Both static and dynamic experiments are conducted on sandstone specimens. Given carefully pulse shaping, the dynamic equilibrium of the inclined specimens can be satisfied, and thus the quasi-static data reduction is employed. The normal and shear stress-strain relationships of specimens are subsequently established. The progressive failure process of the specimen illustrated via high-speed photographs manifests a mixed failure mode accommodating both the shear-dominated failure and the localized tensile damage. The elastic and shear moduli exhibit certain loading-path dependence under quasi-static loading but loading-path insensitivity under high loading rates. Loading rate dependence is evidently demonstrated through the failure characteristics involving fragmentation, compression and shear strength and failure surfaces based on Drucker-Prager criterion. Our proposed method is convenient and reliable to study the dynamic response and failure mechanism of rocks under combined compression-shear loading.

Three-Dimensional Numerical Simulation on Triaxial Failure Mechanical Behavior of Rock-Like Specimen Containing Two Unparallel Fissures

NASA Astrophysics Data System (ADS)

Huang, Yan-Hua; Yang, Sheng-Qi; Zhao, Jian

2016-12-01

A three-dimensional particle flow code (PFC3D) was used for a systematic numerical simulation of the strength failure and cracking behavior of rock-like material specimens containing two unparallel fissures under conventional triaxial compression. The micro-parameters of the parallel bond model were first calibrated using the laboratory results of intact specimens and then validated from the experimental results of pre-fissured specimens under triaxial compression. Numerically simulated stress-strain curves, strength and deformation parameters and macro-failure modes of pre-fissured specimens were all in good agreement with the experimental results. The relationship between stress and the micro-crack numbers was summarized. Crack initiation, propagation and coalescence process of pre-fissured specimens were analyzed in detail. Finally, horizontal and vertical cross sections of numerical specimens were derived from PFC3D. A detailed analysis to reveal the internal damage behavior of rock under triaxial compression was carried out. The experimental and simulated results are expected to improve the understanding of the strength failure and cracking behavior of fractured rock under triaxial compression.

Shear Behaviour and Acoustic Emission Characteristics of Bolted Rock Joints with Different Roughnesses

NASA Astrophysics Data System (ADS)

Wang, Gang; Zhang, Yongzheng; Jiang, Yujing; Liu, Peixun; Guo, Yanshuang; Liu, Jiankang; Ma, Ming; Wang, Ke; Wang, Shugang

2018-06-01

To study shear failure, acoustic emission counts and characteristics of bolted jointed rock-like specimens are evaluated under compressive shear loading. Model joint surfaces with different roughnesses are made of rock-like material (i.e. cement). The jointed rock masses are anchored with bolts with different elongation rates. The characteristics of the shear mechanical properties, the failure mechanism, and the acoustic emission parameters of the anchored joints are studied under different surface roughnesses and anchorage conditions. The shear strength and residual strength increase with the roughness of the anchored joint surface. With an increase in bolt elongation, the shear strength of the anchored joint surface gradually decreases. When the anchored structural plane is sheared, the ideal cumulative impact curve can be divided into four stages: initial emission, critical instability, cumulative energy, and failure. With an increase in the roughness of the anchored joint surface, the peak energy rate and the cumulative number of events will also increase during macro-scale shear failure. With an increase in the bolt elongation, the energy rate and the event number increase during the shearing process. Furthermore, the peak energy rate, peak number of events and cumulative energy will all increase with the bolt elongation. The results of this study can provide guidance for the use of the acoustic emission technique in monitoring and predicting the static shear failure of anchored rock masses.

Effects of bioleaching on the mechanical and chemical properties of waste rocks

NASA Astrophysics Data System (ADS)

Yin, Sheng-Hua; Wu, Ai-Xiang; Wang, Shao-Yong; Ai, Chun-Ming

2012-01-01

Bioleaching processes cause dramatic changes in the mechanical and chemical properties of waste rocks, and play an important role in metal recovery and dump stability. This study focused on the characteristics of waste rocks subjected to bioleaching. A series of experiments were conducted to investigate the evolution of rock properties during the bioleaching process. Mechanical behaviors of the leached waste rocks, such as failure patterns, normal stress, shear strength, and cohesion were determined through mechanical tests. The results of SEM imaging show considerable differences in the surface morphology of leached rocks located at different parts of the dump. The mineralogical content of the leached rocks reflects the extent of dissolution and precipitation during bioleaching. The dump porosity and rock size change under the effect of dissolution, precipitation, and clay transportation. The particle size of the leached rocks decreased due to the loss of rock integrity and the conversion of dry precipitation into fine particles.

Isotropic events observed with a borehole array in the Chelungpu fault zone, Taiwan.

PubMed

Ma, Kuo-Fong; Lin, Yen-Yu; Lee, Shiann-Jong; Mori, Jim; Brodsky, Emily E

2012-07-27

Shear failure is the dominant mode of earthquake-causing rock failure along faults. High fluid pressure can also potentially induce rock failure by opening cavities and cracks, but an active example of this process has not been directly observed in a fault zone. Using borehole array data collected along the low-stress Chelungpu fault zone, Taiwan, we observed several small seismic events (I-type events) in a fluid-rich permeable zone directly below the impermeable slip zone of the 1999 moment magnitude 7.6 Chi-Chi earthquake. Modeling of the events suggests an isotropic, nonshear source mechanism likely associated with natural hydraulic fractures. These seismic events may be associated with the formation of veins and other fluid features often observed in rocks surrounding fault zones and may be similar to artificially induced hydraulic fracturing.

A large landslide in volcanic rock: failure processes, geometry and propagation

NASA Astrophysics Data System (ADS)

Putu Krishna Wijaya, I.; Zangerl, Christian; Straka, Wolfgang; Mergili, Martin; Prasad Pudasaini, Shiva; Arifianti, Yukni

2017-04-01

The Jemblung landslide in Banjarnegara, Indonesia was one of the most destructive landslides in the country since 2006. This landslide caused at least 90 deaths while more than 1300 people were evacuated to safer areas. Concerning the failure mechanisms and type of material, the event can be characterized as a complex landslide (earth slide to earth flow). It originated in volcaniclastic soil/rock, i.e. andesites and lapilli-tuffs of varying degrees of weathering that lie above tuffaceous sandstones, conglomerates, as well as an alternation of shale and brown coal layers. Unmanned aerial vehicle (UAV) data from a secondary database are processed by using photogrammetric software to obtain an overview of the landslide geometry before and after the failure event. Stratigraphic field data and geoelectrical measurements are compared and correlated to build a geological-geometrical model and to estimate the volume of the landslide. Petrographical and XRD analysis are conducted to explain the mineral composition of parent rock and its weathering products. Rainfall as well as seismologic data are collected to study potential trigger and failure mechanisms. The geological-geometrical model of the landslide, digital terrain models of the process area and geotechnical soil properties are combined to model the initial sliding process by applying limit-equilibrium software products. Furthermore, the landslide propagation is simulated with the novel, GIS-based, two-phase mass flow modelling tool r.avaflow in order to improve the understanding of the dynamics of the Jemblung landslide.

Numerical simulation on the deformation and failure of the goaf surrounding rock in Heiwang mine

NASA Astrophysics Data System (ADS)

Shang, Yandong; Guo, Yanpei; Zhang, Wenquan

2018-02-01

The stability of overlying rock mass of mined-out area was simulated using finite difference software FLAC3D according to the gob distribution of Heiwang iron mine. The deformation, failure characteristics of surrounding rock was obtained. The subsidence of strata above the middle mined-out area was the biggest. The maximum subsidence of ground surface was 12.4mm. The farther away from the central goaf was, the smaller the vertical subsidence value was. There was almost no subsidence on the two lateral surrounding rock near mined-out area. There exists the potential danger when cutting along the boundary of goaf. The tensile stress appeared at the top and bottom of the mined-out area. The maximum of tensile stress was 34.7kPa. There was the compressive stress concentration phenomenon in the lateral boundary of mined-out area. The stress concentration coefficient was about 1.5 on both sides of gob. The upper section of the middle goaf was subjected to the tensile failure, and the upper rock mass of both sides was mainly subjected to the tensile-shear failure. The ore pillars on the inner side of the goaf were mainly subjected to the shear failure. When the overlying strata were complete, the possibility of sudden instability of the ore pillar and the sudden subsidence of the ground surface could not occur. The achievements can provide theoretical basis for the processing of the goaf.

Forensic analysis of rockfall scars

NASA Astrophysics Data System (ADS)

de Vilder, Saskia J.; Rosser, Nick J.; Brain, Matthew J.

2017-10-01

We characterise and analyse the detachment (scar) surfaces of rockfalls to understand the mechanisms that underpin their failure. Rockfall scars are variously weathered and comprised of both discontinuity release surfaces and surfaces indicative of fracturing through zones of previously intact rock, known as rock bridges. The presence of rock bridges and pre-existing discontinuities is challenging to quantify due to the difficulty in determining discontinuity persistence below the surface of a rock slope. Rock bridges form an important control in holding blocks onto rockslopes, with their frequency, extent and location commonly modelled from the surface exposure of daylighting discontinuities. We explore an alternative approach to assessing their role, by characterising failure scars. We analyse a database of multiple rockfall scar surfaces detailing the areal extent, shape, and location of broken rock bridges and weathered surfaces. Terrestrial laser scanning and gigapixel imagery were combined to record the detailed texture and surface morphology. From this, scar surfaces were mapped via automated classification based on RGB pixel values. Our analysis of the resulting data from scars on the North Yorkshire coast (UK) indicates a wide variation in both weathering and rock bridge properties, controlled by lithology and associated rock mass structure. Importantly, the proportion of rock bridges in a rockfall failure surface does not increase with failure size. Rather larger failures display fracturing through multiple rock bridges, and in contrast smaller failures fracture occurs only through a single critical rock bridge. This holds implications for how failure mechanisms change with rockfall size and shape. Additionally, the location of rock bridges with respect to the geometry of an incipient rockfall is shown to determine failure mode. Weathering can occur both along discontinuity surfaces and previously broken rock bridges, indicating the sequential stages of progressively detaching rockfall. Our findings have wider implications for hazard assessment where rock slope stability is dependent on the nature of rock bridges, how this is accounted for in slope stability modelling, and the implications of rock bridges on long-term rock slope evolution.

The role of acoustic emission in the study of rock fracture

USGS Publications Warehouse

Lockner, D.

1993-01-01

The development of faults and shear fracture systems over a broad range of temperature and pressure and for a variety of rock types involves the growth and interaction of microcracks. Acoustic emission (AE), which is produced by rapid microcrack growth, is a ubiquitous phenomenon associated with brittle fracture and has provided a wealth of information regarding the failure process in rock. This paper reviews the successes and limitations of AE studies as applied to the fracture process in rock with emphasis on our ability to predict rock failure. Application of laboratory AE studies to larger scale problems related to the understanding of earthquake processes is also discussed. In this context, laboratory studies can be divided into the following categories. 1) Simple counting of the number of AE events prior to sample failure shows a correlation between AE rate and inelastic strain rate. Additional sorting of events by amplitude has shown that AE events obey the power law frequency-magnitude relation observed for earthquakes. These cumulative event count techniques are being used in conjunction with damage mechanics models to determine how damage accumulates during loading and to predict failure. 2) A second area of research involves the location of hypocenters of AE source events. This technique requires precise arrival time data of AE signals recorded over an array of sensors that are essentially a miniature seismic net. Analysis of the spatial and temporal variation of event hypocenters has improved our understanding of the progression of microcrack growth and clustering leading to rock failure. Recently, fracture nucleation and growth have been studied under conditions of quasi-static fault propagation by controlling stress to maintain constant AE rate. 3) A third area of study involves the analysis of full waveform data as recorded at receiver sites. One aspect of this research has been to determine fault plane solutions of AE source events from first motion data. These studies show that in addition to pure tensile and double couple events, a significant number of more complex event types occur in the period leading to fault nucleation. 4) P and S wave velocities (including spatial variations) and attenuation have been obtained by artificially generating acoustic pulses which are modified during passage through the sample. ?? 1993.

Fundamental Research on Percussion Drilling: Improved rock mechanics analysis, advanced simulation technology, and full-scale laboratory investigations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Michael S. Bruno

This report summarizes the research efforts on the DOE supported research project Percussion Drilling (DE-FC26-03NT41999), which is to significantly advance the fundamental understandings of the physical mechanisms involved in combined percussion and rotary drilling, and thereby facilitate more efficient and lower cost drilling and exploration of hard-rock reservoirs. The project has been divided into multiple tasks: literature reviews, analytical and numerical modeling, full scale laboratory testing and model validation, and final report delivery. Literature reviews document the history, pros and cons, and rock failure physics of percussion drilling in oil and gas industries. Based on the current understandings, a conceptualmore » drilling model is proposed for modeling efforts. Both analytical and numerical approaches are deployed to investigate drilling processes such as drillbit penetration with compression, rotation and percussion, rock response with stress propagation, damage accumulation and failure, and debris transportation inside the annulus after disintegrated from rock. For rock mechanics modeling, a dynamic numerical tool has been developed to describe rock damage and failure, including rock crushing by compressive bit load, rock fracturing by both shearing and tensile forces, and rock weakening by repetitive compression-tension loading. Besides multiple failure criteria, the tool also includes a damping algorithm to dissipate oscillation energy and a fatigue/damage algorithm to update rock properties during each impact. From the model, Rate of Penetration (ROP) and rock failure history can be estimated. For cuttings transport in annulus, a 3D numerical particle flowing model has been developed with aid of analytical approaches. The tool can simulate cuttings movement at particle scale under laminar or turbulent fluid flow conditions and evaluate the efficiency of cutting removal. To calibrate the modeling efforts, a series of full-scale fluid hammer drilling tests, as well as single impact tests, have been designed and executed. Both Berea sandstone and Mancos shale samples are used. In single impact tests, three impacts are sequentially loaded at the same rock location to investigate rock response to repetitive loadings. The crater depth and width are measured as well as the displacement and force in the rod and the force in the rock. Various pressure differences across the rock-indentor interface (i.e. bore pressure minus pore pressure) are used to investigate the pressure effect on rock penetration. For hammer drilling tests, an industrial fluid hammer is used to drill under both underbalanced and overbalanced conditions. Besides calibrating the modeling tool, the data and cuttings collected from the tests indicate several other important applications. For example, different rock penetrations during single impact tests may reveal why a fluid hammer behaves differently with diverse rock types and under various pressure conditions at the hole bottom. On the other hand, the shape of the cuttings from fluid hammer tests, comparing to those from traditional rotary drilling methods, may help to identify the dominant failure mechanism that percussion drilling relies on. If so, encouraging such a failure mechanism may improve hammer performance. The project is summarized in this report. Instead of compiling the information contained in the previous quarterly or other technical reports, this report focuses on the descriptions of tasks, findings, and conclusions, as well as the efforts on promoting percussion drilling technologies to industries including site visits, presentations, and publications. As a part of the final deliveries, the 3D numerical model for rock mechanics is also attached.« less

A Micromechanics-Based Elastoplastic Damage Model for Rocks with a Brittle-Ductile Transition in Mechanical Response

NASA Astrophysics Data System (ADS)

Hu, Kun; Zhu, Qi-zhi; Chen, Liang; Shao, Jian-fu; Liu, Jian

2018-06-01

As confining pressure increases, crystalline rocks of moderate porosity usually undergo a transition in failure mode from localized brittle fracture to diffused damage and ductile failure. This transition has been widely reported experimentally for several decades; however, satisfactory modeling is still lacking. The present paper aims at modeling the brittle-ductile transition process of rocks under conventional triaxial compression. Based on quantitative analyses of experimental results, it is found that there is a quite satisfactory linearity between the axial inelastic strain at failure and the confining pressure prescribed. A micromechanics-based frictional damage model is then formulated using an associated plastic flow rule and a strain energy release rate-based damage criterion. The analytical solution to the strong plasticity-damage coupling problem is provided and applied to simulate the nonlinear mechanical behaviors of Tennessee marble, Indiana limestone and Jinping marble, each presenting a brittle-ductile transition in stress-strain curves.

Are Icelandic rock-slope failures paraglacial? Age evaluation of seventeen rock-slope failures in the Skagafjörður area, based on geomorphological stacking, radiocarbon dating and tephrochronology

NASA Astrophysics Data System (ADS)

Mercier, Denis; Coquin, Julien; Feuillet, Thierry; Decaulne, Armelle; Cossart, Etienne; Jónsson, Helgi Pall; Sæmundsson, Þorstein

2017-11-01

In Iceland there are numerous rock-slope failures, especially in the Tertiary basaltic formations of the northern, eastern and northwestern regions. The temporal pattern of rock-slope failures is fundamental for understanding post-glacial events. In the Skagafjörður district, central northern Iceland, 17 rock-slope failures were investigated to determine the age of their occurrence. A geomorphic survey was carried out to identify and characterize landform units, both on the rock-slope failures and in their immediate vicinity. In this coastal area, we used geomorphological stacking which included the relationship between rock-slope failures and raised beaches caused by glacial isostatic rebounds, the chronology of which was established in previous studies. We searched for depressions on the rock-slope failures to then excavate a series of pits and map the stratigraphy. The resulting stratigraphic framework was then validated using (i) radiocarbon dating of wood remains, and (ii) tephrochronology, both of which were complemented by age-depth model calibration. The results confirm that all the rock-slope failures potentially occurred before the Boreal (8 ka), while 94% occurred before the Preboreal (10 ka). They all potentially occurred after the glacial retreat following the maximal ice extent and the Preboreal. More precisely, 11 of them potentially occurred between the Preboreal and the first half of the Holocene. This study demonstrates the relationship between the deglaciation and destabilization of slopes during the paraglacial phase (debuttressing, decompression, glacial isostatic rebound, seismic activity, etc.), which are also controlling factors favouring landsliding, but are difficult to identify for each individual rock-slope failure.

Experimental and numerical study of the failure process and energy mechanisms of rock-like materials containing cross un-persistent joints under uniaxial compression.

PubMed

Cao, Rihong; Cao, Ping; Lin, Hang; Fan, Xiang

2017-01-01

Joints and fissures in natural rocks have a significant influence on the stability of the rock mass, and it is often necessary to evaluate strength failure and crack evolution behavior. In this paper, based on experimental tests and numerical simulation (PFC2D), the macro-mechanical behavior and energy mechanism of jointed rock-like specimens with cross non-persistent joints under uniaxial loading were investigated. The focus was to study the effect of joint dip angle α and intersection angle γ on the characteristic stress, the coalescence modes and the energy release of jointed rock-like specimens. For specimens with γ = 30° and 45°, the UCS (uniaxial compression strength), CIS (crack initiation stress) and CDiS (critical dilatancy stress) increase as α increases from 0° to 75°. When γ = 60° and 75°, the UCS, CIS and CDiS increase as α increases from 0° to 60° and decrease when α is over 60°. Both the inclination angle α and intersection angle γ have great influence on the failure pattern of pre-cracked specimens. With different α and γ, specimens exhibit 4 kinds of failure patterns. Both the experimental and numerical results show that the energy of a specimen has similar trends with characteristic stress as α increases.

The length of pre-existing fissures effects on the mechanical properties of cracked red sandstone and strength design in engineering.

PubMed

Wu, Jiangyu; Feng, Meimei; Yu, Bangyong; Han, Guansheng

2018-01-01

It is important to study the mechanical properties of cracked rock to understand the engineering behavior of cracked rock mass. Consequently, the influence of the length of pre-existing fissures on the strength, deformation, acoustic emission (AE) and failure characteristics of cracked rock specimen was analyzed, and the optimal selection of strength parameter in engineering design was discussed. The results show that the strength parameters (stress of dilatancy onset and uniaxial compressive strength) and deformation parameters (axial strain and circumferential strain at dilatancy onset and peak point) of cracked rock specimen decrease with the increase of the number of pre-existing fissures, and the relations which can use the negative exponential function to fit. Compared with the intact rock specimens, the different degrees of stress drop phenomena were produced in the process of cracked rock specimens when the stress exceeds the dilatancy onset. At this moment, the cracked rock specimens with the existence of stress drop are not instantaneous failure, but the circumferential strain, volumetric strain and AE signals increase burstingly. And the yield platform was presented in the cracked rock specimen with the length of pre-existing fissure more than 23mm, the yield failure was gradually conducted around the inner tip of pre-existing fissure, the development of original fissures and new cracks was evolved fully in rock. However, the time of dilatancy onset is always ahead of the the time of that point with the existence of stress drop. It indicates that the stress of dilatancy onset can be as the parameter of strength design in rock engineering, which can effectively prevent the large deformation of rock. Copyright © 2017 Elsevier B.V. All rights reserved.

A preliminary analysis of failure mechanisms in karst and man-made underground caves in Southern Italy

NASA Astrophysics Data System (ADS)

Parise, M.; Lollino, P.

2011-11-01

Natural and anthropogenic caves may represent a potential hazard for the built environment, due to the occurrence of instability within caves, that may propagate upward and eventually reach the ground surface, inducing the occurrence of sinkholes. In particular, when caves are at shallow depth, the effects at the ground surface may be extremely severe. Apulia region (southern Italy) hosts many sites where hazard associated with sinkholes is very serious due to presence of both natural karst caves and anthropogenic cavities, the latter being mostly represented by underground quarries. The Pliocene-Pleistocene calcarenite (a typical soft rock) was extensively quarried underground, by digging long and complex networks of tunnels. With time, these underground activities have progressively been abandoned and their memory lost, so that many Apulian towns are nowadays located just above the caves, due to urban expansion in the last decades. Therefore, a remarkable risk exists for society, which should not be left uninvestigated. The present contribution deals with the analysis of the most representative failure mechanisms observed in the field for such underground instability processes and the factors that seem to influence the processes, as for example those causing weathering of the rock and the consequent degradation of its physical and mechanical properties. Aimed at exploring the progression of instability of the cavities, numerical analyses have been developed by using both the finite element method for geological settings represented by continuous soft rock mass, and the distinct element method for jointed rock mass conditions. Both the effects of local instability processes occurring underground and the effects of the progressive enlargement of the caves on the overall stability of the rock mass have been investigated, along with the consequent failure mechanisms. In particular, degradation processes of the rock mass, as a consequence of wetting and weathering phenomena in the areas surrounding the caves, have been simulated. The results obtained from the numerical simulations have then been compared with what has been observed during field surveys and a satisfactory agreement between the numerical simulations and the instability processes, as detected in situ, has been noticed.

The geomechanical strength of carbonate rock in Kinta valley, Ipoh, Perak Malaysia

NASA Astrophysics Data System (ADS)

Mazlan, Nur Amanina; Lai, Goh Thian; Razib, Ainul Mardhiyah Mohd; Rafek, Abdul Ghani; Serasa, Ailie Sofyiana; Simon, Norbert; Surip, Noraini; Ern, Lee Khai; Mohamed, Tuan Rusli

2018-04-01

The stability of both cut rocks and underground openings were influenced by the geomechanical strength of rock materials, while the strength characteristics are influenced by both material characteristics and the condition of weathering. This paper present a systematic approach to quantify the rock material strength characteristics for material failure and material & discontinuities failure by using uniaxial compressive strength, point load strength index and Brazilian tensile strength for carbonate rocks. Statistical analysis of the results at 95 percent confidence level showed that the mean value of compressive strength, point load strength index and Brazilian tensile strength for with material failure and material & discontinuities failure were 76.8 ± 4.5 and 41.2 ± 4.1 MPa with standard deviation of 15.2 and 6.5 MPa, respectively. The point load strength index for material failure and material & discontinuities failure were 3.1 ± 0.2 MPa and 1.8 ± 0.3 MPa with standard deviation of 0.9 and 0.6 MPa, respectively. The Brazilian tensile strength with material failure and material & discontinuities failure were 7.1 ± 0.3 MPa and 4.1 ± 0.3 MPa with standard deviation of 1.4 and 0.6 MPa, respectively. The results of this research revealed that the geomechanical strengths of rock material of carbonate rocks for material & discontinuities failure deteriorates approximately ½ from material failure.

Automatic crack detection method for loaded coal in vibration failure process

PubMed Central

Li, Chengwu

2017-01-01

In the coal mining process, the destabilization of loaded coal mass is a prerequisite for coal and rock dynamic disaster, and surface cracks of the coal and rock mass are important indicators, reflecting the current state of the coal body. The detection of surface cracks in the coal body plays an important role in coal mine safety monitoring. In this paper, a method for detecting the surface cracks of loaded coal by a vibration failure process is proposed based on the characteristics of the surface cracks of coal and support vector machine (SVM). A large number of cracked images are obtained by establishing a vibration-induced failure test system and industrial camera. Histogram equalization and a hysteresis threshold algorithm were used to reduce the noise and emphasize the crack; then, 600 images and regions, including cracks and non-cracks, were manually labelled. In the crack feature extraction stage, eight features of the cracks are extracted to distinguish cracks from other objects. Finally, a crack identification model with an accuracy over 95% was trained by inputting the labelled sample images into the SVM classifier. The experimental results show that the proposed algorithm has a higher accuracy than the conventional algorithm and can effectively identify cracks on the surface of the coal and rock mass automatically. PMID:28973032

Automatic crack detection method for loaded coal in vibration failure process.

PubMed

Li, Chengwu; Ai, Dihao

2017-01-01

In the coal mining process, the destabilization of loaded coal mass is a prerequisite for coal and rock dynamic disaster, and surface cracks of the coal and rock mass are important indicators, reflecting the current state of the coal body. The detection of surface cracks in the coal body plays an important role in coal mine safety monitoring. In this paper, a method for detecting the surface cracks of loaded coal by a vibration failure process is proposed based on the characteristics of the surface cracks of coal and support vector machine (SVM). A large number of cracked images are obtained by establishing a vibration-induced failure test system and industrial camera. Histogram equalization and a hysteresis threshold algorithm were used to reduce the noise and emphasize the crack; then, 600 images and regions, including cracks and non-cracks, were manually labelled. In the crack feature extraction stage, eight features of the cracks are extracted to distinguish cracks from other objects. Finally, a crack identification model with an accuracy over 95% was trained by inputting the labelled sample images into the SVM classifier. The experimental results show that the proposed algorithm has a higher accuracy than the conventional algorithm and can effectively identify cracks on the surface of the coal and rock mass automatically.

Riding the Right Wavelet: Quantifying Scale Transitions in Fractured Rocks

NASA Astrophysics Data System (ADS)

Rizzo, Roberto E.; Healy, David; Farrell, Natalie J.; Heap, Michael J.

2017-12-01

The mechanics of brittle failure is a well-described multiscale process that involves a rapid transition from distributed microcracks to localization along a single macroscopic rupture plane. However, considerable uncertainty exists regarding both the length scale at which this transition occurs and the underlying causes that prompt this shift from a distributed to a localized assemblage of cracks or fractures. For the first time, we used an image analysis tool developed to investigate orientation changes at different scales in images of fracture patterns in faulted materials, based on a two-dimensional continuous wavelet analysis. We detected the abrupt change in the fracture pattern from distributed tensile microcracks to localized shear failure in a fracture network produced by triaxial deformation of a sandstone core plug. The presented method will contribute to our ability of unraveling the physical processes at the base of catastrophic rock failure, including the nucleation of earthquakes, landslides, and volcanic eruptions.

Qualitative stability assessment of cut slopes along the National Highway-05 around Jhakri area, Himachal Pradesh, India

NASA Astrophysics Data System (ADS)

Kundu, Jagadish; Sarkar, Kripamoy; Tripathy, Ashutosh; Singh, T. N.

2017-12-01

Several deformation phases in tectonically active Himalayas have rendered the rock masses very complex in terms of structure, lithology and degree of metamorphism. Again, anthropogenic activities such as roads, tunnels and other civil engineering constructions have led to a state of disequilibrium which in many cases, results in failure of rock masses. National Highway-05 around Jhakri area in India is a major connecting route to the China border in the hilly terrains of the state Himachal Pradesh. It cuts through the Himalayan rocks and has a hazardous history of landslides destroying human lives and interrupting communication very frequently. As a contribution towards the mitigation process, a study has been carried out along the highway to analyse kinematic stability and qualitative estimation of rock mass condition through rock mass classification systems. The kinematic analysis shows that the rock slopes are prone to planar and wedge failure. Rock mass rating for most of the locations lies between 7 and 34, representing a poor rock mass quality (Class IV), whereas slope mass rating is more disperse and ranges from 11 to 52 for most of the slopes (Class III, IV and V).

Cold rock coast geomorphology: A quantitative analysis of rock coast processes in Hornsund.

NASA Astrophysics Data System (ADS)

Lim, Michael; Strzelecki, Matt; Kasprzak, Marek; Jaskolski, Marek; Pawlowski, Lukasz; Swirad, Zuzanna; Bell, Heather; Migon, Piotr

2017-04-01

Many arctic coastal systems are experiencing altered thermal and hydrological regimes. Of particular note within the High Arctic is Svalbard, a region undergoing a distinct and sustained rise in mean annual temperatures. Hornsund, at the southern tip of the Svalbard archipelago, is situated at the northern extreme of the North Atlantic current and as such provides a site of unique climate sensitivity with a concentration of geomorphic processes. There is a paucity of studies achieving sufficient resolution to account for geomorphic behaviour and over timescales that allow climatic conditioning to be considered. This research utilises high resolution multiscale surface monitoring and characterisation to quantify and model both contemporary and relic cliff responses in order to revisit one of the first quantitative studies, undertaken almost sixty years ago, on the rates and intensities of rock coast change. The fragmentation and failure in contemporary coastal cliff responses reflects a decrease in the overall rates of change relative to historic rates during a period that has seen the loss of an icefoot that regularly lasted until late summer and a transition to open water coastal dynamics. To investigate the drivers of rock degradation and failure, thermal analyses that characterise both spatial and temporal patterns across and within the rock coast have been used to indicate a potential shift in process activity zones. The significance of localised influences such as storm influences, iceberg influxes and topographic shading highlights some considerations for the development of broader scale models of rock coast evolution.

The impact law of confining pressure and plastic parameter on Dilatancy of rock

NASA Astrophysics Data System (ADS)

Wang, Bin; Zhang, Zhenjie; Zhu, Jiebing

2017-08-01

Based on cyclic loading-unloading triaxle test of marble, the double parameter dilation angle model is established considering confining pressure effect and plastic parameter. Research shows that not only the strength but also the militancy behavior is highly depended on its confining pressure and plastic parameter during process of failure. Dilation angle evolution law shows obvious nonlinear characteristic almost with a rapid increase to the peak and then decrease gradually with plastic increasing, and the peak dilation angle value is inversely proportional with confining pressure. The proposed double parameter nonlinear dilation angle model can be used to well describe the Dilatancy of rock, which helps to understand the failure mechanism of surrounding rock mass and predict the range of plastic zone.

Elastic Rock Heterogeneity Controls Brittle Rock Failure during Hydraulic Fracturing

NASA Astrophysics Data System (ADS)

Langenbruch, C.; Shapiro, S. A.

2014-12-01

For interpretation and inversion of microseismic data it is important to understand, which properties of the reservoir rock control the occurrence probability of brittle rock failure and associated seismicity during hydraulic stimulation. This is especially important, when inverting for key properties like permeability and fracture conductivity. Although it became accepted that seismic events are triggered by fluid flow and the resulting perturbation of the stress field in the reservoir rock, the magnitude of stress perturbations, capable of triggering failure in rocks, can be highly variable. The controlling physical mechanism of this variability is still under discussion. We compare the occurrence of microseismic events at the Cotton Valley gas field to elastic rock heterogeneity, obtained from measurements along the treatment wells. The heterogeneity is characterized by scale invariant fluctuations of elastic properties. We observe that the elastic heterogeneity of the rock formation controls the occurrence of brittle failure. In particular, we find that the density of events is increasing with the Brittleness Index (BI) of the rock, which is defined as a combination of Young's modulus and Poisson's ratio. We evaluate the physical meaning of the BI. By applying geomechanical investigations we characterize the influence of fluctuating elastic properties in rocks on the probability of brittle rock failure. Our analysis is based on the computation of stress fluctuations caused by elastic heterogeneity of rocks. We find that elastic rock heterogeneity causes stress fluctuations of significant magnitude. Moreover, the stress changes necessary to open and reactivate fractures in rocks are strongly related to fluctuations of elastic moduli. Our analysis gives a physical explanation to the observed relation between elastic heterogeneity of the rock formation and the occurrence of brittle failure during hydraulic reservoir stimulations. A crucial factor for understanding seismicity in unconventional reservoirs is the role of anisotropy of rocks. We evaluate an elastic VTI rock model corresponding to a shale gas reservoir in the Horn River Basin to understand the relation between stress, event occurrence and elastic heterogeneity in anisotropic rocks.

Hydromechanical coupling in fractured rock masses: mechanisms and processes of selected case studies

NASA Astrophysics Data System (ADS)

Zangerl, Christian

2015-04-01

Hydromechanical (HM) coupling in fractured rock play an important role when events including dam failures, landslides, surface subsidences due to water withdrawal or drainage, injection-induced earthquakes and others are analysed. Generally, hydromechanical coupling occurs when a rock mass contain interconnected pores and fractures which are filled with water and pore/fracture pressures evolves. In the on hand changes in the fluid pressure can lead to stress changes, deformations and failures of the rock mass. In the other hand rock mass stress changes and deformations can alter the hydraulic properties and fluid pressures of the rock mass. Herein well documented case studies focussing on surface subsidence due to water withdrawal, reversible deformations of large-scale valley flanks and failure as well as deformation processes of deep-seated rock slides in fractured rock masses are presented. Due to pore pressure variations HM coupling can lead to predominantly reversible rock mass deformations. Such processes can be considered by the theory of poroelasticity. Surface subsidence reaching magnitudes of few centimetres and are caused by water drainage into deep tunnels are phenomenas which can be assigned to processes of poroelasticity. Recently, particular focus was given on large tunnelling projects to monitor and predict surface subsidence in fractured rock mass in oder to avoid damage of surface structures such as dams of large reservoirs. It was found that surface subsidence due to tunnel drainage can adversely effect infrastructure when pore pressure drawdown is sufficiently large and spatially extended and differential displacements which can be amplified due to topographical effects e.g. valley closure are occurring. Reversible surface deformations were also ascertained on large mountain slopes and summits with the help of precise deformation measurements i.e. permanent GPS or episodic levelling/tacheometric methods. These reversible deformations are often in the range of millimetres to a very few centimetres and can be linked to annual groundwater fluctuations. Due to pore pressure variations HM coupling can influence seepage forces and effective stresses in the rock mass. Effective stress changes can adversely affect the stability and deformation behaviour of deep-seated rock slides by influencing the shear strength or the time dependent (viscous) material behaviour of the basal shear zone. The shear strength of active shear zones is often reasonably well described by Coulomb's law. In Coulomb's law the operative normal stresses to the shear surface/zone are effective stresses and hence pore pressures which should be taken into account reduces the shear strength. According to the time dependent material behaviour a few effective stress based viscous models exists which are able to consider pore pressures. For slowly moving rock slides HM coupling could be highly relevant when low-permeability clayey-silty shear zones (fault gouges) are existing. An important parameters therefore is the hydraulic diffusivity, which is controlled by the permeability and fluid-pore compressibility of the shear zone, and by fluid viscosity. Thus time dependent pore pressure diffusion in the shear zone can either control the stability condition or the viscous behaviour (creep) of the rock slide. Numerous cases studies show that HM coupling can effect deformability, shear strength and time dependent behaviour of fractured rock masses. A process-based consideration can be important to avoid unexpected impacts on infrastructures and to understand complex rock mass as well rock slide behaviour.

Failure Characteristics of Granite Influenced by Sample Height-to-Width Ratios and Intermediate Principal Stress Under True-Triaxial Unloading Conditions

NASA Astrophysics Data System (ADS)

Li, Xibing; Feng, Fan; Li, Diyuan; Du, Kun; Ranjith, P. G.; Rostami, Jamal

2018-05-01

The failure modes and peak unloading strength of a typical hard rock, Miluo granite, with particular attention to the sample height-to-width ratio (between 2 and 0.5), and the intermediate principal stress was investigated using a true-triaxial test system. The experimental results indicate that both sample height-to-width ratios and intermediate principal stress have an impact on the failure modes, peak strength and severity of rockburst in hard rock under true-triaxial unloading conditions. For longer rectangular specimens, the transition of failure mode from shear to slabbing requires higher intermediate principal stress. With the decrease in sample height-to-width ratios, slabbing failure is more likely to occur under the condition of lower intermediate principal stress. For same intermediate principal stress, the peak unloading strength monotonically increases with the decrease in sample height-to-width. However, the peak unloading strength as functions of intermediate principal stress for different types of rock samples (with sample height-to-width ratio of 2, 1 and 0.5) all present the pattern of initial increase, followed by a subsequent decrease. The curves fitted to octahedral shear stress as a function of mean effective stress also validate the applicability of the Mogi-Coulomb failure criterion for all considered rock sizes under true-triaxial unloading conditions, and the corresponding cohesion C and internal friction angle φ are calculated. The severity of strainburst of granite depends on the sample height-to-width ratios and intermediate principal stress. Therefore, different supporting strategies are recommended in deep tunneling projects and mining activities. Moreover, the comparison of test results of different σ 2/ σ 3 also reveals the little influence of minimum principal stress on failure characteristics of granite during the true-triaxial unloading process.

Seismically damaged regolith as self-organized fragile geological feature

NASA Astrophysics Data System (ADS)

Sleep, Norman H.

2011-12-01

The S-wave velocity in the shallow subsurface within seismically active regions self-organizes so that typical strong dynamic shear stresses marginally exceed the Coulomb elastic limit. The dynamic velocity from major strike-slip faults yields simple dimensional relations. The near-field velocity pulse is essentially a Love wave. The dynamic shear strain is the ratio of the measured particle velocity over the deep S-wave velocity. The shallow dynamic shear stress is this quantity times the local shear modulus. The dynamic shear traction on fault parallel vertical planes is finite at the free surface. Coulomb failure occurs on favorably oriented fractures and internally in intact rock. I obtain the equilibrium shear modulus by starting a sequence of earthquakes with intact stiff rock extending all the way to the surface. The imposed dynamic shear strain in stiff rock causes Coulomb failure at shallow depths and leaves cracks in it wake. Cracked rock is more compliant than the original intact rock. Cracked rock is also weaker in friction, but shear modulus changes have a larger effect. Each subsequent event causes additional shallow cracking until the rock becomes compliant enough that it just reaches Coulomb failure over a shallow depth range of tens to hundreds of meters. Further events maintain the material at the shear modulus as a function where it just fails. The formalism provided in the paper yields reasonable representation of the S-wave velocity in exhumed sediments near Cajon Pass and the San Fernando Valley of California. A general conclusion is that shallow rocks in seismically active areas just become nonlinear during typical shaking. This process causes transient changes in S-wave velocity, but not strong nonlinear attenuation of seismic waves. Wave amplitudes significantly larger than typical ones would strongly attenuate and strongly damage the rock.

Factors controlling the structures of magma chambers in basaltic volcanoes

NASA Technical Reports Server (NTRS)

Wilson, L.; Head, James W.

1991-01-01

The depths, vertical extents, and lateral extents of magma chambers and their formation are discussed. The depth to the center of a magma chamber is most probably determined by the density structure of the lithosphere; this process is explained. It is commonly assumed that magma chambers grow until the stress on the roof, floor, and side-wall boundaries exceed the strength of the wall rocks. Attempts to grow further lead to dike propagation events which reduce the stresses below the critical values of rock failure. The tensile or compressive failure of the walls is discussed with respect to magma migration. The later growth of magma chambers is accomplished by lateral dike injection into the country rocks. The factors controlling the patterns of growth and cooling of such dikes are briefly mentioned.

Interaction of thermal and mechanical processes in steep permafrost rock walls: A conceptual approach

NASA Astrophysics Data System (ADS)

Draebing, D.; Krautblatter, M.; Dikau, R.

2014-12-01

Degradation of permafrost rock wall decreases stability and can initiate rock slope instability of all magnitudes. Rock instability is controlled by the balance of shear forces and shear resistances. The sensitivity of slope stability to warming results from a complex interplay of shear forces and resistances. Conductive, convective and advective heat transport processes act to warm, degrade and thaw permafrost in rock walls. On a seasonal scale, snow cover changes are a poorly understood key control of the timing and extent of thawing and permafrost degradation. We identified two potential critical time windows where shear forces might exceed shear resistances of the rock. In early summer combined hydrostatic and cryostatic pressure can cause a peak in shear force exceeding high frozen shear resistance and in autumn fast increasing shear forces can exceed slower increasing shear resistance. On a multiannual system scale, shear resistances change from predominantly rock-mechanically to ice-mechanically controlled. Progressive rock bridge failure results in an increase of sensitivity to warming. Climate change alters snow cover and duration and, hereby, thermal and mechanical processes in the rock wall. Amplified thawing of permafrost will result in higher rock slope instability and rock fall activity. We present a holistic conceptual approach connecting thermal and mechanical processes, validate parts of the model with geophysical and kinematic data and develop future scenarios to enhance understanding on system scale.

Dynamic Stability of the Rate, State, Temperature, and Pore Pressure Friction Model at a Rock Interface

NASA Astrophysics Data System (ADS)

Sinha, Nitish; Singh, Arun K.; Singh, Trilok N.

2018-05-01

In this article, we study numerically the dynamic stability of the rate, state, temperature, and pore pressure friction (RSTPF) model at a rock interface using standard spring-mass sliding system. This particular friction model is a basically modified form of the previously studied friction model namely the rate, state, and temperature friction (RSTF). The RSTPF takes into account the role of thermal pressurization including dilatancy and permeability of the pore fluid due to shear heating at the slip interface. The linear stability analysis shows that the critical stiffness, at which the sliding becomes stable to unstable or vice versa, increases with the coefficient of thermal pressurization. Critical stiffness, on the other hand, remains constant for small values of either dilatancy factor or hydraulic diffusivity, but the same decreases as their values are increased further from dilatancy factor (˜ 10^{ - 4} ) and hydraulic diffusivity (˜ 10^{ - 9} {m}2 {s}^{ - 1} ) . Moreover, steady-state friction is independent of the coefficient of thermal pressurization, hydraulic diffusivity, and dilatancy factor. The proposed model is also used for predicting time of failure of a creeping interface of a rock slope under the constant gravitational force. It is observed that time of failure decreases with increase in coefficient of thermal pressurization and hydraulic diffusivity, but the dilatancy factor delays the failure of the rock fault under the condition of heat accumulation at the creeping interface. Moreover, stiffness of the rock-mass also stabilizes the failure process of the interface as the strain energy due to the gravitational force accumulates in the rock-mass before it transfers to the sliding interface. Practical implications of the present study are also discussed.

Discrete Element Method and its application to materials failure problem on the example of Brazilian Test

NASA Astrophysics Data System (ADS)

Klejment, Piotr; Kosmala, Alicja; Foltyn, Natalia; Dębski, Wojciech

2017-04-01

The earthquake focus is the point where a rock under external stress starts to fracture. Understanding earthquake nucleation and earthquake dynamics requires thus understanding of fracturing of brittle materials. This, however, is a continuing problem and enduring challenge to geoscience. In spite of significant progress we still do not fully understand the failure of rock materials due to extreme stress concentration in natural condition. One of the reason of this situation is that information about natural or induced seismic events is still not sufficient for precise description of physical processes in seismic foci. One of the possibility of improving this situation is using numerical simulations - a powerful tool of contemporary physics. For this reason we used an advanced implementation of the Discrete Element Method (DEM). DEM's main task is to calculate physical properties of materials which are represented as an assembly of a great number of particles interacting with each other. We analyze the possibility of using DEM for describing materials during so called Brazilian Test. Brazilian Test is a testing method to obtain the tensile strength of brittle material. One of the primary reasons for conducting such simulations is to measure macroscopic parameters of the rock sample. We would like to report our efforts of describing the fracturing process during the Brazilian Test from the microscopic point of view and give an insight into physical processes preceding materials failure.

Energy evolution mechanism in process of Sandstone failure and energy strength criterion

NASA Astrophysics Data System (ADS)

Wang, Yunfei; Cui, Fang

2018-07-01

To reveal the inherent relation between energy change and confining pressure during the process of sandstone damage, and its characteristics of energy storage and energy dissipation in different deformation stage. Obtaining the mechanical parameters by testing the Sandstone of two1 coal seam roof under uniaxial compression in Zhaogu coalmine, using Particle Flow Code (PFC) and fish program to get the meso-mechanical parameters, studying Sandstone energy evolution mechanism under different confining pressures, and deducing energy strength criterion based on energy principle of rock failure, some main researching results are reached as follows: with the increasing of confining pressure, the Sandstone yield stage and ductility increases, but brittleness decreases; Under higher confining pressure, the elastic strain energy of Sandstone before peak approximately keeps constant in a certain strain range, and rock absorbs all the energy which converts into surface energy required for internal damage development; Under lower confining pressure, Sandstone no longer absorbs energy with increasing strain after peak under lower confining pressure, while it sequentially absorbs energy under higher confining pressure; Under lower confining pressure, the energy Sandstone before peak absorbed mainly converts into elastic strain energy, while under higher confining pressure, dissipation energy significantly increases before peak, which indicates that the degree rock strength loss is higher under higher confining pressure; with the increasing of confining pressure, the limit of elastic strain energy increases and there exists a favourable linear variation relationship; At the peak point, the ratio of elastic strain energy to total energy of Sandstone nonlinearly decreases, while the ratio of dissipation energy to total energy nonlinearly increases with the increasing of confining pressure; According to energy evolution mechanism of rock failure, an energy strength criterion is derived. The criterion equation includes lithology constants and three principal stresses, and its physical meaning is clear. This criterion has an evident advantage than Hoek-Brown and Drucker-Prager criterion in calculation accuracy and can commendably describe rock failure characteristics.

Frequency-Based Precursory Acoustic Emission Failure Sequences In Sedimentary And Igneous Rocks Under Uniaxial Compression

NASA Astrophysics Data System (ADS)

Colin, C.; Anderson, R. C.; Chasek, M. D.; Peters, G. H.; Carey, E. M.

2016-12-01

Identifiable precursors to rock failure have been a long pursued and infrequently encountered phenomena in rock mechanics and acoustic emission studies. Since acoustic emissions in compressed rocks were found to follow the Gutenberg-Richter law, failure-prediction strategies based on temporal changes in b-value have been recurrent. In this study, we extend on the results of Ohnaka and Mogi [Journal of Geophysical Research, Vol. 87, No. B5, p. 3873-3884, (1982)], where the bulk frequency characteristics of rocks under incremental uniaxial compression were observed in relation to changes in b-value before and after failure. Based on the proposition that the number of low-frequency acoustic emissions is proportional to the number of high-amplitude acoustic emissions in compressed rocks, Ohnaka and Mogi (1982) demonstrated that b-value changes in granite and andesite cores under incremental uniaxial compression could be expressed in terms of the percent abundance of low-frequency events. In this study, we attempt to demonstrate that the results of Ohnaka and Mogi (1982) hold true for different rock types (basalt, sandstone, and limestone) and different sample geometries (rectangular prisms). In order to do so, the design of the compression tests was kept similar to that of Ohnaka and Mogi (1982). Two high frequency piezoelectric transducers of 1 MHz and a 500 kHz coupled to the sides of the samples detected higher and lower frequency acoustic emission signals. However, rather than gathering parametric data from an analog signal using a counter as per Ohnaka and Mogi (1982), we used an oscilloscope as an analog to digital converter interfacing with LabVIEW 2015 to record the complete waveforms. The digitally stored waveforms were then processed, detecting acoustic emission events using a statistical method, and filtered using a 2nd order Butterworth filter. In addition to calculating the percent abundance of low-frequency events over time, the peak frequency of the acoustic emissions over time was observable due to the digital method of waveform capture. This allows for a more direct comparison between frequency characteristics and b-values of rocks under compression and investigates the viability of observing frequency behavior over time as a method of rock failure prediction.

Progressive failure of sheeted rock slopes: the 2009–2010 Rhombus Wall rock falls in Yosemite Valley, California, USA

USGS Publications Warehouse

Stock, Greg M.; Martel, Stephen J.; Collins, Brian D.; Harp, Edwin L.

2012-01-01

Progressive rock-fall failures in natural rock slopes are common in many environments, but often elude detailed quantitative documentation and analysis. Here we present high-resolution photography, video, and laser scanning data that document spatial and temporal patterns of a 15-month-long sequence of at least 14 rock falls from the Rhombus Wall, a sheeted granitic cliff in Yosemite Valley, California. The rock-fall sequence began on 26 August 2009 with a small failure at the tip of an overhanging rock slab. Several hours later, a series of five rock falls totaling 736 m3progressed upward along a sheeting joint behind the overhanging slab. Over the next 3 weeks, audible cracking occurred on the Rhombus Wall, suggesting crack propagation, while visual monitoring revealed opening of a sheeting joint adjacent to the previous failure surface. On 14 September 2009 a 110 m3 slab detached along this sheeting joint. Additional rock falls between 30 August and 20 November 2010, totaling 187 m3, radiated outward from the initial failure area along cliff (sub)parallel sheeting joints. We suggest that these progressive failures might have been related to stress redistributions accompanying propagation of sheeting joints behind the cliff face. Mechanical analyses indicate that tensile stresses should occur perpendicular to the cliff face and open sheeting joints, and that sheeting joints should propagate parallel to a cliff face from areas of stress concentrations. The analyses also account for how sheeting joints can propagate to lengths many times greater than their depths behind cliff faces. We posit that as a region of failure spreads across a cliff face, stress concentrations along its margin will spread with it, promoting further crack propagation and rock falls.

Experimental Study On The Effect Of Micro-Cracks On Brazilian Tensile Strength

NASA Astrophysics Data System (ADS)

Wang, Xiangyu

2015-12-01

For coal mine ground control issues, it is necessary to propose a failure criteria accounting for the transversely isotropic behaviors of rocks. Hence, it is very helpful to provide experimental data for the validation of the failure criteria. In this paper, the method for preparing transversely isotropic specimens and the scheme of the Brazilian tensile strength test are presented. Results obtained from Brazilian split tests under dry and water-saturated conditions reflect the effect of the development direction β of the structural plane, such as the bedding fissure, on the tensile strength, ultimate displacement, failure mode, and the whole splitting process. The results show that the tensile strength decreases linearly with increasing β. The softening coefficient of the tensile strength shows a sinusoidal function. The values of the slope and inflection point for the curve vary at the different stages of the Brazilian test. The failure mode of the rock specimen presented in this paper generally coincides with the standard Brazilian splitting failure mode. Based on the test results, the major influencing factors for the Brazilian splitting strength are analyzed and a mathematical model for solving the Brazilian splitting strength is proposed. The findings in this paper would greatly benefit the coal mine ground control studies when the surrounding rocks of interest show severe transversely isotropic behaviors.

Rock mechanics issues in completion and stimulation operations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Warpinski, N.R.

Rock mechanisms parameters such as the in situ stresses, elastic properties, failure characteristics, and poro-elastic response are important to most completion and stimulation operations. Perforating, hydraulic fracturing, wellbore stability, and sand production are examples of technology that are largely controlled by the rock mechanics of the process. While much research has been performed in these areas, there has been insufficient application that research by industry. In addition, there are new research needs that must be addressed for technology advancement.

Prediction of Brittle Failure for TBM Tunnels in Anisotropic Rock: A Case Study from Northern Norway

NASA Astrophysics Data System (ADS)

Dammyr, Øyvind

2016-06-01

Prediction of spalling and rock burst is especially important for hard rock TBM tunneling, because failure can have larger impact than in a drill and blast tunnel and ultimately threaten excavation feasibility. The majority of research on brittle failure has focused on rock types with isotropic behavior. This paper gives a review of existing theory and its application before a 3.5-m-diameter TBM tunnel in foliated granitic gneiss is used as a case to study brittle failure characteristics of anisotropic rock. Important aspects that should be considered in order to predict brittle failure in anisotropic rock are highlighted. Foliation is responsible for considerable strength anisotropy and is believed to influence the preferred side of v-shaped notch development in the investigated tunnel. Prediction methods such as the semi- empirical criterion, the Hoek- Brown brittle parameters, and the non-linear damage initiation and spalling limit method give reliable results; but only as long as the angle between compression axis and foliation in uniaxial compressive tests is relevant, dependent on the relation between tunnel trend/plunge, strike/dip of foliation, and tunnel boundary stresses. It is further demonstrated that local in situ stress variations, for example, due to the presence of discontinuities, can have profound impact on failure predictions. Other carefully documented case studies into the brittle failure nature of rock, in particular anisotropic rock, are encouraged in order to expand the existing and relatively small database. This will be valuable for future TBM planning and construction stages in highly stressed brittle anisotropic rock.

Multidisciplinary research leading to utilization of extraterrestrial resources

NASA Technical Reports Server (NTRS)

1972-01-01

Progress of the research accomplished during fiscal year 1972 is reported. The summaries presented include: (1) background analysis and coordination, (2) surface properties of rock in simulated lunar environment, (3) rock failure processes, strength and elastic properties in simulated lunar environment, (4) thermal fragmentation, and thermophysical and optical properties in simulated lunar environment, and (5) use of explosives on the moon.

Rho-GTPase effector ROCK phosphorylates cofilin in actin-meditated cytokinesis during mouse oocyte meiosis.

PubMed

Duan, Xing; Liu, Jun; Dai, Xiao-Xin; Liu, Hong-Lin; Cui, Xiang-Shun; Kim, Nam-Hyung; Wang, Zhen-Bo; Wang, Qiang; Sun, Shao-Chen

2014-02-01

During oocyte meiosis, a spindle forms in the central cytoplasm and migrates to the cortex. Subsequently, the oocyte extrudes a small body and forms a highly polarized egg; this process is regulated primarily by actin. ROCK is a Rho-GTPase effector that is involved in various cellular functions, such as stress fiber formation, cell migration, tumor cell invasion, and cell motility. In this study, we investigated possible roles for ROCK in mouse oocyte meiosis. ROCK was localized around spindles after germinal vesicle breakdown and was colocalized with cytoplasmic actin and mitochondria. Disrupting ROCK activity by RNAi or an inhibitor resulted in cell cycle progression and polar body extrusion failure. Time-lapse microscopy showed that this may have been due to spindle migration and cytokinesis defects, as chromosomes segregated but failed to extrude a polar body and then realigned. Actin expression at oocyte membranes and in cytoplasm was significantly decreased after these treatments. Actin caps were also disrupted, which was confirmed by a failure to form cortical granule-free domains. The mitochondrial distribution was also disrupted, which indicated that mitochondria were involved in the ROCK-mediated actin assembly. In addition, the phosphorylation levels of Cofilin, a downstream molecule of ROCK, decreased after disrupting ROCK activity. Thus, our results indicated that a ROCK-Cofilin-actin pathway regulated meiotic spindle migration and cytokinesis during mouse oocyte maturation.

A Numerical Study on Toppling Failure of a Jointed Rock Slope by Using the Distinct Lattice Spring Model

NASA Astrophysics Data System (ADS)

Lian, Ji-Jian; Li, Qin; Deng, Xi-Fei; Zhao, Gao-Feng; Chen, Zu-Yu

2018-02-01

In this work, toppling failure of a jointed rock slope is studied by using the distinct lattice spring model (DLSM). The gravity increase method (GIM) with a sub-step loading scheme is implemented in the DLSM to mimic the loading conditions of a centrifuge test. A classical centrifuge test for a jointed rock slope, previously simulated by the finite element method and the discrete element model, is simulated by using the GIM-DLSM. Reasonable boundary conditions are obtained through detailed comparisons among existing numerical solutions with experimental records. With calibrated boundary conditions, the influences of the tensional strength of the rock block, cohesion and friction angles of the joints, as well as the spacing and inclination angles of the joints, on the flexural toppling failure of the jointed rock slope are investigated by using the GIM-DLSM, leading to some insight into evaluating the state of flexural toppling failure for a jointed slope and effectively preventing the flexural toppling failure of jointed rock slopes.

Release of radiogenic noble gases as a new signal of rock deformation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bauer, Stephen J.; Gardner, W. Payton; Lee, Hyunwoo

In this paper we investigate the release of radiogenic noble gas isotopes during mechanical deformation. We developed an analytical system for dynamic mass spectrometry of noble gas composition and helium release rate of gas produced during mechanical deformation of rocks. Our results indicate that rocks release accumulated radiogenic helium and argon from mineral grains as they undergo deformation. We found that the release of accumulated 4He and 40Ar from rocks follows a reproducible pattern and can provide insight into the deformation process. Increased gas release can be observed before dilation, and macroscopic failure is observed during high-pressure triaxial rock deformationmore » experiments. Accumulated radiogenic noble gases can be released due to fracturing of mineral grains during small-scale strain in Earth materials. Helium and argon are highly mobile, conservative species and could be used to provide information on changes in the state of stress and strain in Earth materials, and as an early warning signal of macroscopic failure. These results pave the way for the use of noble gases to trace and monitor rock deformation for earthquake prediction and a variety of other subsurface engineering projects.« less

Release of radiogenic noble gases as a new signal of rock deformation

DOE PAGES

Bauer, Stephen J.; Gardner, W. Payton; Lee, Hyunwoo

2016-10-09

In this paper we investigate the release of radiogenic noble gas isotopes during mechanical deformation. We developed an analytical system for dynamic mass spectrometry of noble gas composition and helium release rate of gas produced during mechanical deformation of rocks. Our results indicate that rocks release accumulated radiogenic helium and argon from mineral grains as they undergo deformation. We found that the release of accumulated 4He and 40Ar from rocks follows a reproducible pattern and can provide insight into the deformation process. Increased gas release can be observed before dilation, and macroscopic failure is observed during high-pressure triaxial rock deformationmore » experiments. Accumulated radiogenic noble gases can be released due to fracturing of mineral grains during small-scale strain in Earth materials. Helium and argon are highly mobile, conservative species and could be used to provide information on changes in the state of stress and strain in Earth materials, and as an early warning signal of macroscopic failure. These results pave the way for the use of noble gases to trace and monitor rock deformation for earthquake prediction and a variety of other subsurface engineering projects.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Park, Jung-Wook; Rutqvist, Jonny; Ryu, Dongwoo

The present study is aimed at numerically examining the thermal-hydrological-mechanical (THM) processes within the rock mass surrounding a cavern used for thermal energy storage (TES). We considered a cylindrical rock cavern with a height of 50 m and a radius of 10 m storing thermal energy of 350ºC as a conceptual TES model and simulated its operation for 30 years using THM coupled numerical modeling. At first, the insulator performance was not considered for the purpose of investigating the possible coupled THM behavior of the surrounding rock mass; then, the effects of an insulator were examined for different insulator thicknesses.more » The key concerns were focused on the hydro-thermal multiphase flow and heat transport in the rock mass around the thermal storage cavern, the effect of evaporation of rock mass, thermal impact on near the ground surface and the mechanical behavior of the surrounding rock mass. It is shown that the rock temperature around the cavern rapidly increased in the early stage and, consequently, evaporation of groundwater occurred, raising the fluid pressure. However, evaporation and multiphase flow did not have a significant effect on the heat transfer and mechanical behavior in spite of the high-temperature (350ºC) heat source. The simulations showed that large-scale heat flow around a cavern was expected to be conductiondominated for a reasonable value of rock mass permeability. Thermal expansion as a result of the heating of the rock mass from the storage cavern led to a ground surface uplift on the order of a few centimeters and to the development of tensile stress above the storage cavern, increasing the potentials for shear and tensile failures after a few years of the operation. Finally, the analysis showed that high tangential stress in proximity of the storage cavern can some shear failure and local damage, although large rock wall failure could likely be controlled with appropriate insulators and reinforcement.« less

Rock failure analysis by combined thermal weakening and water jet impact

NASA Technical Reports Server (NTRS)

Nayfeh, A. H.

1976-01-01

The influence of preheating on the initiation of fracture in rocks subjected to the impingement of a continuous water jet is studied. Preheating the rock is assumed to degrade its mechanical properties and strength in accordance with existing experimental data. The water jet is assumed to place a quasi-static loading on the surface of the rock. The loading is approximated by elementary functions which permit analytic computation of the induced stresses in a rock half-space. The resulting stresses are subsequently coupled with the Griffith criteria for tensile failure to estimate the change, due to heating, in the critical stagnation pressure and velocity of the water jet required to cause failure in the rock.

Coupled fluid and solid evolution in analogue volcanic vents

NASA Astrophysics Data System (ADS)

Solovitz, Stephen A.; Ogden, Darcy E.; Kim, Dave (Dae-Wook); Kim, Sang Young

2014-07-01

Volcanic eruptions emit rock particulates and gases at high speed and pressure, which change the shape of the surrounding rock. Simplified analytical solutions, field studies, and numerical models suggest that this process plays an important role in the behavior and hazards associated with explosive volcanic eruptions. Here we present results from a newly developed laboratory-scale apparatus designed to study this coupled process. The experiments used compressed air jets expanding into the laboratory through fabricated rock analogue material, which evolves through time during the experiment. The compressed air was injected at approximately 2.5 times atmospheric pressure. We fabricated rock analogues from sand and steel powder samples with a three-dimensional printing process. We studied the fluid development using phase-locked particle image velocimetry, while simultaneously observing the solid development via a video camera. We found that the fluid response was much more rapid than that of the solid, permitting a quasi-steady approximation. In most cases, the solid vent flared out rapidly, increasing its diameter by 20 to 100%. After the initial expansion, the vent and flow field achieved a near-steady condition for a long duration. The new expanded vent shapes permitted lower vent exit pressures and larger jet radii. In one experiment, after an initial vent shape development and establishment of steady flow behavior, rock failure occurred a second time, resulting in a new exit diameter and new steady state. This second failure was not precipitated by changes in the nozzle flow condition, and it radically changed the downstream flow dynamics. This experiment suggests that the brittle nature of volcanic host rock enables sudden vent expansion in the middle of an eruption without requiring a change in the conduit flow.

Failure Behavior of Granite Affected by Confinement and Water Pressure and Its Influence on the Seepage Behavior by Laboratory Experiments.

PubMed

Cheng, Cheng; Li, Xiao; Li, Shouding; Zheng, Bo

2017-07-14

Failure behavior of granite material is paramount for host rock stability of geological repositories for high-level waste (HLW) disposal. Failure behavior also affects the seepage behavior related to transportation of radionuclide. Few of the published studies gave a consistent analysis on how confinement and water pressure affect the failure behavior, which in turn influences the seepage behavior of the rock during the damage process. Based on a series of laboratory experiments on NRG01 granite samples cored from Alxa area, a candidate area for China's HLW disposal, this paper presents some detailed observations and analyses for a better understanding on the failure mechanism and seepage behavior of the samples under different confinements and water pressure. The main findings of this study are as follows: (1) Strength reduction properties were found for the granite under water pressure. Besides, the complete axial stress-strain curves show more obvious yielding process in the pre-peak region and a more gradual stress drop in the post-peak region; (2) Shear fracturing pattern is more likely to form in the granite samples with the effect of water pressure, even under much lower confinements, than the predictions from the conventional triaxial compressive results; (3) Four stages of inflow rate curves are divided and the seepage behaviors are found to depend on the failure behavior affected by the confinement and water pressure.

Can we use ice calving on glacier fronts as a proxy for rock slope failures?

NASA Astrophysics Data System (ADS)

Abellan, Antonio; Penna, Ivanna; Daicz, Sergio; Carrea, Dario; Derron, Marc-Henri; Jaboyedoff, Michel; Riquelme, Adrian; Tomas, Roberto

2015-04-01

Ice failures on glacier terminus show very similar fingerprints to rock-slope failure (RSF) processes, nevertheless, the investigation of gravity-driven instabilities that shape rock cliffs and glacier's fronts are currently dissociated research topics. Since both materials (ice and rocks) have very different rheological properties, the development of a progressive failure on mountain cliffs occurs at a much slower rate than that observed on glacier fronts, which leads the latter a good proxy for investigating RSF. We utilized a terrestrial Laser Scanner (Ilris-LR system from Optech) for acquiring successive 3D point clouds of one of the most impressive calving glacier fronts, the Perito Moreno glacier located in the Southern Patagonian Ice Fields (Argentina). We scanned the glacier terminus during five days (from 10th to 14th of March 2014) with very high accuracy (0.7cm standard deviation of the error at 100m) and a high density of information (200 points per square meter). Each data series was acquired at a mean interval of 20 minutes. The maximum attainable range for the utilized wavelength of the Ilris-LR system (1064 nm) was around 500 meters over massive ice (showing no-significant loss of information), being this distance considerably reduced on crystalline or wet ice short after the occurrence of calving events. As for the data treatment, we have adapted our innovative algorithms originally developed for the investigation of both precursory deformation and rockfalls to study calving events. By comparing successive three-dimensional datasets, we have investigated not only the magnitude and frequency of several ice failures at the glacier's terminus (ranging from one to thousands of cubic meters), but also the characteristic geometrical features of each failure. In addition, we were able to quantify a growing strain rate on several areas of the glacier's terminus shortly after their final collapse. For instance, we investigated the spatial extent of the differential pre-failure deformation, together with its length and duration, showing very similar acceleration patterns than that observed on rock slopes at their 3rd creep stage. We then documented the differential strain rates observed at different parts of the glacier's terminus, and correlated the areas affected with a progressive acceleration on the strain rate with those that had finally calved. Finally, we also observed that, similarly as it occurs on rock slopes, the investigation of the mechanical discontinuities (crevasses) observed at the glacier controlled the different front failure mechanisms observed at the glacier front. Thanks to the so-built analogies between rock and ice gravity driven instability phenomena, this interdisciplinary research could constitute a great insight in the investigation of RSF endangering human population and infrastructures.

Influence of microscale heterogeneity and microstructure on the tensile behavior of crystalline rocks

NASA Astrophysics Data System (ADS)

Mahabadi, O. K.; Tatone, B. S. A.; Grasselli, G.

2014-07-01

This study investigates the influence of microscale heterogeneity and microcracks on the failure behavior and mechanical response of a crystalline rock. The thin section analysis for obtaining the microcrack density is presented. Using micro X-ray computed tomography (μCT) scanning of failed laboratory specimens, the influence of heterogeneity and, in particular, biotite grains on the brittle fracture of the specimens is discussed and various failure patterns are characterized. Three groups of numerical simulations are presented, which demonstrate the role of microcracks and the influence of μCT-based and stochastically generated phase distributions. The mechanical response, stress distribution, and fracturing process obtained by the numerical simulations are also discussed. The simulation results illustrate that heterogeneity and microcracks should be considered to accurately predict the tensile strength and failure behavior of the sample.

Rupture Dynamics and Scaling Behavior of Hydraulically Stimulated Micro-Earthquakes in a Shale Reservoir

NASA Astrophysics Data System (ADS)

Viegas, G. F.; Urbancic, T.; Baig, A. M.

2014-12-01

In hydraulic fracturing completion programs fluids are injected under pressure into fractured rock formations to open escape pathways for trapped hydrocarbons along pre-existing and newly generated fractures. To characterize the failure process, we estimate static and dynamic source and rupture parameters, such as dynamic and static stress drop, radiated energy, seismic efficiency, failure modes, failure plane orientations and dimensions, and rupture velocity to investigate the rupture dynamics and scaling relations of micro-earthquakes induced during a hydraulic fracturing shale completion program in NE British Columbia, Canada. The relationships between the different parameters combined with the in-situ stress field and rock properties provide valuable information on the rupture process giving insights into the generation and development of the fracture network. Approximately 30,000 micro-earthquakes were recorded using three multi-sensor arrays of high frequency geophones temporarily placed close to the treatment area at reservoir depth (~2km). On average the events have low radiated energy, low dynamic stress and low seismic efficiency, consistent with the obtained slow rupture velocities. Events fail in overshoot mode (slip weakening failure model), with fluids lubricating faults and decreasing friction resistance. Events occurring in deeper formations tend to have faster rupture velocities and are more efficient in radiating energy. Variations in rupture velocity tend to correlate with variation in depth, fault azimuth and elapsed time, reflecting a dominance of the local stress field over other factors. Several regions with different characteristic failure modes are identifiable based on coherent stress drop, seismic efficiency, rupture velocities and fracture orientations. Variations of source parameters with rock rheology and hydro-fracture fluids are also observed. Our results suggest that the spatial and temporal distribution of events with similar characteristic rupture behaviors can be used to determine reservoir geophysical properties, constrain reservoir geo-mechanical models, classify dynamic rupture processes for fracture models and improve fracture treatment designs.

Beyond debuttressing: Mechanics of paraglacial rock slope damage during repeat glacial cycles

NASA Astrophysics Data System (ADS)

Grämiger, Lorenz M.; Moore, Jeffrey R.; Gischig, Valentin S.; Ivy-Ochs, Susan; Loew, Simon

2017-04-01

Cycles of glaciation impose mechanical stresses on underlying bedrock as glaciers advance, erode, and retreat. Fracture initiation and propagation constitute rock mass damage and act as preparatory factors for slope failures; however, the mechanics of paraglacial rock slope damage remain poorly characterized. Using conceptual numerical models closely based on the Aletsch Glacier region of Switzerland, we explore how in situ stress changes associated with fluctuating ice thickness can drive progressive rock mass failure preparing future slope instabilities. Our simulations reveal that glacial cycles as purely mechanical loading and unloading phenomena produce relatively limited new damage. However, ice fluctuations can increase the criticality of fractures in adjacent slopes, which may in turn increase the efficacy of fatigue processes. Bedrock erosion during glaciation promotes significant new damage during first deglaciation. An already weakened rock slope is more susceptible to damage from glacier loading and unloading and may fail completely. We find that damage kinematics are controlled by discontinuity geometry and the relative position of the glacier; ice advance and retreat both generate damage. We correlate model results with mapped landslides around the Great Aletsch Glacier. Our result that most damage occurs during first deglaciation agrees with the relative age of the majority of identified landslides. The kinematics and dimensions of a slope failure produced in our models are also in good agreement with characteristics of instabilities observed in the field. Our results extend simplified assumptions of glacial debuttressing, demonstrating in detail how cycles of ice loading, erosion, and unloading drive paraglacial rock slope damage.

New perspectives on the transition between discrete fracture, fragmentation, and pulverization during brittle failure of rocks

NASA Astrophysics Data System (ADS)

Griffith, W. A.; Ghaffari, H.; Barber, T. J.; Borjas, C.

2015-12-01

The motions of Earth's tectonic plates are typically measured in millimeters to tens of centimeters per year, seemingly confirming the generally-held view that tectonic processes are slow, and have been throughout Earth's history. In line with this perspective, the vast majority of laboratory rock mechanics research focused on failure in the brittle regime has been limited to experiments utilizing slow loading rates. On the other hand, many natural processes that pose significant risk for humans (e.g., earthquakes and extraterrestrial impacts), as well as risks associated with human activities (blow-outs, explosions, mining and mine failures, projectile penetration), occur at rates that are hundreds to thousands of times faster than those typically simulated in the laboratory. Little experimental data exists to confirm or calibrate theoretical models explaining the connection between these dramatic events and the pulverized rocks found in fault zones, impacts, or explosions; however the experimental data that does exist is thought-provoking: At the earth's surface, the process of brittle fracture passes through a critical transition in rocks at high strain rates (101-103s-1) between regimes of discrete fracture and distributed fragmentation, accompanied by a dramatic increase in strength. Previous experimental works on this topic have focused on key thresholds (e.g., peak stress, peak strain, average strain rate) that define this transition, but more recent work suggests that this transition is more fundamentally dependent on characteristics (e.g., shape) of the loading pulse and related microcrack dynamics, perhaps explaining why for different lithologies different thresholds more effectively define the pulverization transition. In this presentation we summarize some of our work focused on this transition, including the evolution of individual defects at the microscopic, microsecond scale and the energy budget associated with the brittle fragmentation process as a function of lithology and loading pulse characteristics.

Experimental studies the evolution of stress-strain state in structured rock specimens under uniaxial loading

NASA Astrophysics Data System (ADS)

Oparin, Viktor; Tsoy, Pavel; Usoltseva, Olga; Semenov, Vladimir

2014-05-01

The aim of this study was to analyze distribution and development of stress-stress state in structured rock specimens subject to uniaxial loading to failure. Specific attention was paid to possible oscillating motion of structural elements of the rock specimens under constraints (pre-set stresses at the boundaries of the specimens) and the kinetic energy fractals. The detailed studies into the micro-level stress-strain state distribution and propagation over acting faces of rock specimens subject to uniaxial loading until failure, using automated digital speckle photography analyzer ALMEC-tv, have shown that: • under uniaxial stiff loading of prismatic sandstone, marble and sylvinite specimens on the Instron-8802 servohydraulic testing machine at the mobile grip displacement rate 0.02-0.2 mm/min, at a certain level of stressing, low-frequency micro-deformation processes originate in the specimens due to slow (quasi-static) force; • the amplitude of that deformation-wave processes greatly depends on the micro-loading stage: — at the elastic deformation stage, under the specimen stress lower than half ultimate strength of the specimen, there are no oscillations of microstrains; —at the nonlinearly elastic deformation stage, under stress varied from 0.5 to 1 ultimate strength of the specimens, the amplitudes of microstrains grow, including the descending stage 3; the oscillation frequency f=0.5-4 Hz; —at the residual strength stage, the amplitudes of the microstrains drop abruptly (3-5 times) as against stages 2 and 3; • in the elements of the scanned specimen surface in the region with the incipient crack, the microstrain rate amplitudes are a few times higher than in the undamged surface region of the same specimen. Sometimes, deformation rate greatly grows with increase in the load. The authors have used the energy scanning function of the deformation-wave processes in processing experimental speckle-photography data on the surface of the test specimen subject to loading until failure.

Derivation and application of an analytical rock displacement solution on rectangular cavern wall using the inverse mapping method.

PubMed

Gao, Mingzhong; Yu, Bin; Qiu, Zhiqiang; Yin, Xiangang; Li, Shengwei; Liu, Qiang

2017-01-01

Rectangular caverns are increasingly used in underground engineering projects, the failure mechanism of rectangular cavern wall rock is significantly different as a result of the cross-sectional shape and variations in wall stress distributions. However, the conventional computational method always results in a long-winded computational process and multiple displacement solutions of internal rectangular wall rock. This paper uses a Laurent series complex method to obtain a mapping function expression based on complex variable function theory and conformal transformation. This method is combined with the Schwarz-Christoffel method to calculate the mapping function coefficient and to determine the rectangular cavern wall rock deformation. With regard to the inverse mapping concept, the mapping relation between the polar coordinate system within plane ς and a corresponding unique plane coordinate point inside the cavern wall rock is discussed. The disadvantage of multiple solutions when mapping from the plane to the polar coordinate system is addressed. This theoretical formula is used to calculate wall rock boundary deformation and displacement field nephograms inside the wall rock for a given cavern height and width. A comparison with ANSYS numerical software results suggests that the theoretical solution and numerical solution exhibit identical trends, thereby demonstrating the method's validity. This method greatly improves the computing accuracy and reduces the difficulty in solving for cavern boundary and internal wall rock displacements. The proposed method provides a theoretical guide for controlling cavern wall rock deformation failure.

Derivation and application of an analytical rock displacement solution on rectangular cavern wall using the inverse mapping method

PubMed Central

Gao, Mingzhong; Qiu, Zhiqiang; Yin, Xiangang; Li, Shengwei; Liu, Qiang

2017-01-01

Rectangular caverns are increasingly used in underground engineering projects, the failure mechanism of rectangular cavern wall rock is significantly different as a result of the cross-sectional shape and variations in wall stress distributions. However, the conventional computational method always results in a long-winded computational process and multiple displacement solutions of internal rectangular wall rock. This paper uses a Laurent series complex method to obtain a mapping function expression based on complex variable function theory and conformal transformation. This method is combined with the Schwarz-Christoffel method to calculate the mapping function coefficient and to determine the rectangular cavern wall rock deformation. With regard to the inverse mapping concept, the mapping relation between the polar coordinate system within plane ς and a corresponding unique plane coordinate point inside the cavern wall rock is discussed. The disadvantage of multiple solutions when mapping from the plane to the polar coordinate system is addressed. This theoretical formula is used to calculate wall rock boundary deformation and displacement field nephograms inside the wall rock for a given cavern height and width. A comparison with ANSYS numerical software results suggests that the theoretical solution and numerical solution exhibit identical trends, thereby demonstrating the method’s validity. This method greatly improves the computing accuracy and reduces the difficulty in solving for cavern boundary and internal wall rock displacements. The proposed method provides a theoretical guide for controlling cavern wall rock deformation failure. PMID:29155892

The Mohr-Coulomb criterion for intact rock strength and friction - a re-evaluation and consideration of failure under polyaxial stresses

NASA Astrophysics Data System (ADS)

Hackston, A.; Rutter, E.

2015-12-01

Abstract Darley Dale and Pennant sandstones were tested under conditions of both axisymmetric shortening and extension normal to bedding. These are the two extremes of loading under polyaxial stress conditions. Failure under generalized stress conditions can be predicted from the Mohr-Coulomb failure criterion under axisymmetric compression conditions provided the best form of polyaxial failure criterion is known. The sandstone data are best reconciled using the Mogi (1967) empirical criterion. Fault plane orientations produced vary greatly with respect to the maximum compression direction in the two loading configurations. The normals to the Mohr-Coulomb failure envelopes do not predict the orientations of the fault planes eventually produced. Frictional sliding on variously inclined sawcuts and failure surfaces produced in intact rock samples was also investigated. Friction coefficient is not affected by fault plane orientation in a given loading configuration, but friction coefficients in extension were systematically lower than in compression for both rock types and could be reconciled by a variant on the Mogi (1967) failure criterion. Friction data for these and other porous sandstones accord well with the Byerlee (1977) generalization about rock friction being largely independent of rock type. For engineering and geodynamic modelling purposes, the stress-state dependent friction coefficient should be used for sandstones, but it is not known to what extent this might apply to other rock types.

Implementation of Smoothed Particle Hydrodynamics for Detonation of Explosive with Application to Rock Fragmentation

NASA Astrophysics Data System (ADS)

Pramanik, R.; Deb, D.

2015-07-01

The paper presents a methodology in the SPH framework to analyze physical phenomena those occur in detonation process of an explosive. It mainly investigates the dynamic failure mechanism in surrounding brittle rock media under blast-induced stress wave and expansion of high pressure product gases. A program burn model is implemented along with JWL equation of state to simulate the reaction zone in between unreacted explosive and product gas. Numerical examples of detonation of one- and two-dimensional explosive slab have been carried out to investigate the effect of reaction zone in detonation process and outward dispersion of gaseous product. The results are compared with those obtained from existing solutions. A procedure is also developed in SPH framework to apply continuity conditions between gas and rock interface boundaries. The modified Grady-Kipp damage model for the onset of tensile yielding and Drucker-Prager model for shear failure are implemented for elasto-plastic analysis of rock medium. The results show that high compressive stress causes high crack density in the vicinity of blast hole. The major principal stress (tensile) is responsible for forming radial cracks from the blast hole. Spalling zones are also developed due to stress waves reflected from the free surfaces.

Mechanical Behavior of Brittle Rock-Like Specimens with Pre-existing Fissures Under Uniaxial Loading: Experimental Studies and Particle Mechanics Approach

NASA Astrophysics Data System (ADS)

Cao, Ri-hong; Cao, Ping; Lin, Hang; Pu, Cheng-zhi; Ou, Ke

2016-03-01

Joints and fissures with similar orientation or characteristics are common in natural rocks; the inclination and density of the fissures affect the mechanical properties and failure mechanism of the rock mass. However, the strength, crack coalescence pattern, and failure mode of rock specimens containing multi-fissures have not been studied comprehensively. In this paper, combining similar material testing and discrete element numerical method (PFC2D), the peak strength and failure characteristics of rock-like materials with multi-fissures are explored. Rock-like specimens were made of cement and sand and pre-existing fissures created by inserting steel shims into cement mortar paste and removing them during curing. The peak strength of multi-fissure specimens depends on the fissure angle α (which is measured counterclockwise from horizontal) and fissure number ( N f). Under uniaxial compressional loading, the peak strength increased with increasing α. The material strength was lowest for α = 25°, and highest for α = 90°. The influence of N f on the peak strength depended on α. For α = 25° and 45°, N f had a strong effect on the peak strength, while for higher α values, especially for the 90° sample, there were no obvious changes in peak strength with different N f. Under uniaxial compression, the coalescence modes between the fissures can be classified into three categories: S-mode, T-mode, and M-mode. Moreover, the failure mode can be classified into four categories: mixed failure, shear failure, stepped path failure, and intact failure. The failure mode of the specimen depends on α and N f. The peak strength and failure modes in the numerically simulated and experimental results are in good agreement.

Crack identification and evolution law in the vibration failure process of loaded coal

NASA Astrophysics Data System (ADS)

Li, Chengwu; Ai, Dihao; Sun, Xiaoyuan; Xie, Beijing

2017-08-01

To study the characteristics of coal cracks produced in the vibration failure process, we set up a static load and static and dynamic combination load failure test simulation system, prepared with different particle size, formation pressure, and firmness coefficient coal samples. Through static load damage testing of coal samples and then dynamic load (vibration exciter) and static (jack) combination destructive testing, the crack images of coal samples under the load condition were obtained. Combined with digital image processing technology, an algorithm of crack identification with high precision and in real-time is proposed. With the crack features of the coal samples under different load conditions as the research object, we analyzed the distribution of cracks on the surface of the coal samples and the factors influencing crack evolution using the proposed algorithm and a high-resolution industrial camera. Experimental results showed that the major portion of the crack after excitation is located in the rear of the coal sample where the vibration exciter cannot act. Under the same disturbance conditions, crack size and particle size exhibit a positive correlation, while crack size and formation pressure exhibit a negative correlation. Soft coal is more likely to lead to crack evolution than hard coal, and more easily causes instability failure. The experimental results and crack identification algorithm provide a solid basis for the prevention and control of instability and failure of coal and rock mass, and they are helpful in improving the monitoring method of coal and rock dynamic disasters.

The Mohr-Coulomb criterion for intact rock strength and friction - a re-evaluation and consideration of failure under polyaxial stresses

NASA Astrophysics Data System (ADS)

Hackston, Abigail; Rutter, Ernest

2016-04-01

Darley Dale and Pennant sandstones were tested under conditions of both axisymmetric shortening and extension normal to bedding. These are the two extremes of loading under polyaxial stress conditions. Failure under generalized stress conditions can be predicted from the Mohr-Coulomb failure criterion under axisymmetric shortening conditions, provided the best form of polyaxial failure criterion is known. The sandstone data are best reconciled using the Mogi (1967) empirical criterion. Fault plane orientations produced vary greatly with respect to the maximum compressive stress direction in the two loading configurations. The normals to the Mohr-Coulomb failure envelopes do not predict the orientations of the fault planes eventually produced. Frictional sliding on variously inclined saw cuts and failure surfaces produced in intact rock samples was also investigated. Friction coefficient is not affected by fault plane orientation in a given loading configuration, but friction coefficients in extension were systematically lower than in compression for both rock types. Friction data for these and other porous sandstones accord well with the Byerlee (1978) generalization about rock friction being largely independent of rock type. For engineering and geodynamic modelling purposes, the stress-state-dependent friction coefficient should be used for sandstones, but it is not known to what extent this might apply to other rock types.

Numerical Studies on the Failure Process of Heterogeneous Brittle Rocks or Rock-Like Materials under Uniaxial Compression

PubMed Central

Guo, Songfeng; Qi, Shengwen; Zou, Yu; Zheng, Bowen

2017-01-01

In rocks or rock-like materials, the constituents, e.g. quartz, calcite and biotite, as well as the microdefects have considerably different mechanical properties that make such materials heterogeneous at different degrees. The failure of materials subjected to external loads is a cracking process accompanied with stress redistribution due to material heterogeneity. However, the latter cannot be observed from the experiments in laboratory directly. In this study, the cracking and stress features during uniaxial compression process are numerically studied based on a presented approach. A plastic strain dependent strength model is implemented into the continuous numerical tool—Fast Lagrangian Analysis of Continua in three Dimensions (FLAC3D), and the Gaussian statistical function is adopted to depict the heterogeneity of mechanical parameters including elastic modulus, friction angle, cohesion and tensile strength. The mean parameter μ and the coefficient of variance (hcv, the ratio of mean parameter to standard deviation) in the function are used to define the mean value and heterogeneity degree of the parameters, respectively. The results show that this numerical approach can perfectly capture the general features of brittle materials including fracturing process, AE events as well as stress-strain curves. Furthermore, the local stress disturbance is analyzed and the crack initiation stress threshold is identified based on the AE events process and stress-strain curves. It is shown that the stress concentration always appears in the undamaged elements near the boundary of damaged sites. The peak stress and crack initiation stress are both heterogeneity dependent, i.e., a linear relation exists between the two stress thresholds and hcv. The range of hcv is suggested as 0.12 to 0.21 for most rocks. The stress concentration degree is represented by a stress concentration factor and found also heterogeneity dominant. Finally, it is found that there exists a consistent tendency between the local stress difference and the AE events process. PMID:28772738

Numerical Studies on the Failure Process of Heterogeneous Brittle Rocks or Rock-Like Materials under Uniaxial Compression.

PubMed

Guo, Songfeng; Qi, Shengwen; Zou, Yu; Zheng, Bowen

2017-04-01

In rocks or rock-like materials, the constituents, e.g. quartz, calcite and biotite, as well as the microdefects have considerably different mechanical properties that make such materials heterogeneous at different degrees. The failure of materials subjected to external loads is a cracking process accompanied with stress redistribution due to material heterogeneity. However, the latter cannot be observed from the experiments in laboratory directly. In this study, the cracking and stress features during uniaxial compression process are numerically studied based on a presented approach. A plastic strain dependent strength model is implemented into the continuous numerical tool-Fast Lagrangian Analysis of Continua in three Dimensions (FLAC 3D ), and the Gaussian statistical function is adopted to depict the heterogeneity of mechanical parameters including elastic modulus, friction angle, cohesion and tensile strength. The mean parameter μ and the coefficient of variance ( h cv , the ratio of mean parameter to standard deviation) in the function are used to define the mean value and heterogeneity degree of the parameters, respectively. The results show that this numerical approach can perfectly capture the general features of brittle materials including fracturing process, AE events as well as stress-strain curves. Furthermore, the local stress disturbance is analyzed and the crack initiation stress threshold is identified based on the AE events process and stress-strain curves. It is shown that the stress concentration always appears in the undamaged elements near the boundary of damaged sites. The peak stress and crack initiation stress are both heterogeneity dependent, i.e., a linear relation exists between the two stress thresholds and h cv . The range of h cv is suggested as 0.12 to 0.21 for most rocks. The stress concentration degree is represented by a stress concentration factor and found also heterogeneity dominant. Finally, it is found that there exists a consistent tendency between the local stress difference and the AE events process.

Blueschist- and Eclogite facies Pseudotachylytes: Products of Earthquakes in Collision- and Subduction zones

NASA Astrophysics Data System (ADS)

Andersen, T. B.; Austrheim, H.; John, T.; Medvedev, S.; Mair, K.

2009-04-01

Pseudotachylytes are the products of violent geological processes such as metorite impacts and seismic faulting. The fault-rock weakening processes leading to release of earthquakes are commonly related to phenomena such as grain size reduction and gouge formation, pressurization of pore-fluids and in some cases to melting by frictional heating. Explaining the frequently observed intermediate and deep earthquakes by brittle failure is, however, inherently difficult to reconcile because of extremely high normal stresses occuring at depth. In recent years several mechanisms for seismic events on deep faults have been suggested. These include: a) The most commonly accepted mechanism, dehydration embrittlement coupled to prograde metamorphic dehydration of wet rocks, such as serpentinites, at depth. b) Grain-size dependent flow-laws coupled with shear heating instability has been suggested as an alternative to explain repeated seismic faulting in Wadati-Benioff zones. c) Self-localized-thermal-runaway (SLTR) has been forwarded as a mechanism for ultimate failure of visco-elastic materials and as mechanism to explain the co-existence of shear zones and pseudotachylyte fault veins formed at eclogite facies conditions. All these mechanism point to the importance of metamorphism and/or metasomatism in understanding the mechanism(s) of intermediate- and deep earthquakes. Exhumed high to ultra-high pressure [(U)HP] metamorphic rocks are recognized in many orogenic belts. These complexes provide avenues to study a number of important products of geological processes including earthquakes with hypocentres at great depths. (U)HP co-seismic fault rocks are difficult to find in the field; nevertheless, a number of occurrences of co-seismic fault rocks from such complexes have been described after the initial discovery of such rocks in Norway (see: Austrheim and Boundy, Science 1994). In this talk we review some observations and interpretations based on these hitherto rarely observed but important co-seismic fault rocks from deep-crust and mantle complexes.

Coupled thermal-hydrological-mechanical behavior of rock mass surrounding a high-temperature thermal energy storage cavern at shallow depth

DOE PAGES

Park, Jung-Wook; Rutqvist, Jonny; Ryu, Dongwoo; ...

2016-01-15

The present study is aimed at numerically examining the thermal-hydrological-mechanical (THM) processes within the rock mass surrounding a cavern used for thermal energy storage (TES). We considered a cylindrical rock cavern with a height of 50 m and a radius of 10 m storing thermal energy of 350ºC as a conceptual TES model and simulated its operation for 30 years using THM coupled numerical modeling. At first, the insulator performance was not considered for the purpose of investigating the possible coupled THM behavior of the surrounding rock mass; then, the effects of an insulator were examined for different insulator thicknesses.more » The key concerns were focused on the hydro-thermal multiphase flow and heat transport in the rock mass around the thermal storage cavern, the effect of evaporation of rock mass, thermal impact on near the ground surface and the mechanical behavior of the surrounding rock mass. It is shown that the rock temperature around the cavern rapidly increased in the early stage and, consequently, evaporation of groundwater occurred, raising the fluid pressure. However, evaporation and multiphase flow did not have a significant effect on the heat transfer and mechanical behavior in spite of the high-temperature (350ºC) heat source. The simulations showed that large-scale heat flow around a cavern was expected to be conductiondominated for a reasonable value of rock mass permeability. Thermal expansion as a result of the heating of the rock mass from the storage cavern led to a ground surface uplift on the order of a few centimeters and to the development of tensile stress above the storage cavern, increasing the potentials for shear and tensile failures after a few years of the operation. Finally, the analysis showed that high tangential stress in proximity of the storage cavern can some shear failure and local damage, although large rock wall failure could likely be controlled with appropriate insulators and reinforcement.« less

Evaluation of strength and failure of brittle rock containing initial cracks under lithospheric conditions

NASA Astrophysics Data System (ADS)

Li, Xiaozhao; Qi, Chengzhi; Shao, Zhushan; Ma, Chao

2018-02-01

Natural brittle rock contains numerous randomly distributed microcracks. Crack initiation, growth, and coalescence play a predominant role in evaluation for the strength and failure of brittle rocks. A new analytical method is proposed to predict the strength and failure of brittle rocks containing initial microcracks. The formulation of this method is based on an improved wing crack model and a suggested micro-macro relation. In this improved wing crack model, the parameter of crack angle is especially introduced as a variable, and the analytical stress-crack relation considering crack angle effect is obtained. Coupling the proposed stress-crack relation and the suggested micro-macro relation describing the relation between crack growth and axial strain, the stress-strain constitutive relation is obtained to predict the rock strength and failure. Considering different initial microcrack sizes, friction coefficients and confining pressures, effects of crack angle on tensile wedge force acting on initial crack interface are studied, and effects of crack angle on stress-strain constitutive relation of rocks are also analyzed. The strength and crack initiation stress under different crack angles are discussed, and the value of most disadvantaged angle triggering crack initiation and rock failure is founded. The analytical results are similar to the published study results. Rationality of this proposed analytical method is verified.

Risk Analysis of Earth-Rock Dam Failures Based on Fuzzy Event Tree Method

PubMed Central

Fu, Xiao; Gu, Chong-Shi; Su, Huai-Zhi; Qin, Xiang-Nan

2018-01-01

Earth-rock dams make up a large proportion of the dams in China, and their failures can induce great risks. In this paper, the risks associated with earth-rock dam failure are analyzed from two aspects: the probability of a dam failure and the resulting life loss. An event tree analysis method based on fuzzy set theory is proposed to calculate the dam failure probability. The life loss associated with dam failure is summarized and refined to be suitable for Chinese dams from previous studies. The proposed method and model are applied to one reservoir dam in Jiangxi province. Both engineering and non-engineering measures are proposed to reduce the risk. The risk analysis of the dam failure has essential significance for reducing dam failure probability and improving dam risk management level. PMID:29710824

Energy Evolution Mechanism and Confining Pressure Effect of Granite under Triaxial Loading-Unloading Cycles

NASA Astrophysics Data System (ADS)

Wang, Hao; Miao, Sheng-jun

2018-05-01

Rock mass undergoes some deformational failure under the action of external loads, a process known to be associated with energy dissipation and release. A triaxial loading-unloading cycle test was conducted on granite in order to investigate the energy evolution pattern of rock mass under the action of external loads. The study results demonstrated: (1) The stress peaks increased by 50% and 22% respectively and the pre-peak weakening became more apparent in the ascending process of the confining pressure from 10MPa to 30MPa; the area enclosed by the hysteresis loop corresponding to 30MPa diminished by nearly 60% than that corresponding to 10MPa, indicating a higher confining pressure prohibits rock mass from plastic deformation and shifts strain toward elastic deformation. (2) In the vicinity of the strength limit, the slope of dissipation energy increased to 1.6 from the original 0.7 and the dissipation energy grew at an accelerating rate, demonstrating stronger propagation and convergence of internal cracks. (3) At a pressure of 70% of the stress peak, the elastic energy of the granite accounted for 88% of its peak value, suggesting the rock mechanical energy from the outside mostly changes into the elastic energy inside the rock, with little energy loss.(4) Prior to test specimen failure, the axial bearing capacity dropped with a decreasing confining pressure in an essentially linear way, and the existence of confirming pressure played a role in stabilizing the axial bearing capacity.

The prehistoric Vajont rockslide: An updated geological model

NASA Astrophysics Data System (ADS)

Paronuzzi, Paolo; Bolla, Alberto

2012-10-01

This study presents the detailed reconstruction of the entire structure of the prehistoric Vajont rockslide (about 270-300 million m3 of rocks and debris) for the first time, describing the complex geometry and the characteristic superimposition of distinct rigid blocks on a very thick shear zone. The prehistoric Vajont rockslide was characterized by an enormous 'en masse' motion of a rigid overlying rock mass (100-130 m thick) that moved downslope, sliding onto a very thick shear zone (40-50 m thick, on average) made up of a chaotic assemblage of blocks, limestone angular gravel, and high plasticity clays (montmorillonitic clays). Coarse loose sediments, still exposed on the 9 October 1963 detachment surface, are always associated with large blocks made of strongly fractured rock masses (Fonzaso Formation: middle-upper Jurassic) preserving the stratification. The blocks of stratified and folded limestone sequences appear to be 'sheared off' from the underlying bedrock and can be considered as displaced rock masses planed off by the motion of the overlying rigid rock mass ('rock mass shavings'). The prehistoric Vajont rockslide was characterized by a multistage failure with a marked retrogressive evolution. The first rupture (Pian del Toc block) rapidly destabilized the upper slope, mobilizing a second rock mass block (Pian della Pozza block) that, in turn, determined the multiple rupture of the revealed shear zone material (Massalezza lobe). Even if the exact timing of the different phases is not known, the entire multistaged failure process was very rapid. At the end of the multistage retrogressive failure, the slope morphology of the northern toe of Mt. Toc was drastically changed and the large failed rock mass settled into the preexisting Vajont Valley assuming the unusual chair-like geometry. The Vajont rockslide represents a very significant example on how a complex geological situation, if not adequately analyzed and reconstructed, can lead to dangerous misinterpretations or even to erroneous engineering-geological and geotechnical models. Accurate fieldwork and modern technologies can be fundamental in solving such a very intriguing 'geological puzzle.'

Strength Restoration of Cracked Sandstone and Coal under a Uniaxial Compression Test and Correlated Damage Source Location Based on Acoustic Emissions.

PubMed

Feng, Xiaowei; Zhang, Nong; Zheng, Xigui; Pan, Dongjiang

2015-01-01

Underground rock masses have shown a general trend of natural balance over billions of years of ground movement. Nonetheless, man-made underground constructions disturb this balance and cause rock stability failure. Fractured rock masses are frequently encountered in underground constructions, and this study aims to restore the strength of rock masses that have experienced considerable fracturing under uniaxial compression. Coal and sandstone from a deep-buried coal mine were chosen as experimental subjects; they were crushed by uniaxial compression and then carefully restored by a chemical adhesive called MEYCO 364 with an innovative self-made device. Finally, the restored specimens were crushed once again by uniaxial compression. Axial stress, axial strain, circumferential strain, and volumetric strain data for the entire process were fully captured and are discussed here. An acoustic emission (AE) testing system was adopted to cooperate with the uniaxial compression system to provide better definitions for crack closure thresholds, crack initiation thresholds, crack damage thresholds, and three-dimensional damage source locations in intact and restored specimens. Several remarkable findings were obtained. The restoration effects of coal are considerably better than those of sandstone because the strength recovery coefficient of the former is 1.20, whereas that of the latter is 0.33, which indicates that MEYCO 364 is particularly valid for fractured rocks whose initial intact peak stress is less than that of MEYCO 364. Secondary cracked traces of restored sandstone almost follow the cracked traces of the initial intact sandstone, and the final failure is mainly caused by decoupling between the adhesive and the rock mass. However, cracked traces of restored coal only partially follow the traces of intact coal, with the final failure of the restored coal being caused by both bonding interface decoupling and self-breakage in coal. Three-dimensional damage source locations manifest such that AE events are highly correlated with a strength recovery coefficient; the AE events show a decreasing tendency when the coefficient is larger than 1, and vice versa. This study provides a feasible scheme for the reinforcement of fractured rock masses in underground constructions and reveals an internal mechanism of the crushing process for restored rock masses, which has certain instructive significance.

Strength Restoration of Cracked Sandstone and Coal under a Uniaxial Compression Test and Correlated Damage Source Location Based on Acoustic Emissions

PubMed Central

Feng, Xiaowei; Zhang, Nong; Zheng, Xigui; Pan, Dongjiang

2015-01-01

Underground rock masses have shown a general trend of natural balance over billions of years of ground movement. Nonetheless, man-made underground constructions disturb this balance and cause rock stability failure. Fractured rock masses are frequently encountered in underground constructions, and this study aims to restore the strength of rock masses that have experienced considerable fracturing under uniaxial compression. Coal and sandstone from a deep-buried coal mine were chosen as experimental subjects; they were crushed by uniaxial compression and then carefully restored by a chemical adhesive called MEYCO 364 with an innovative self-made device. Finally, the restored specimens were crushed once again by uniaxial compression. Axial stress, axial strain, circumferential strain, and volumetric strain data for the entire process were fully captured and are discussed here. An acoustic emission (AE) testing system was adopted to cooperate with the uniaxial compression system to provide better definitions for crack closure thresholds, crack initiation thresholds, crack damage thresholds, and three-dimensional damage source locations in intact and restored specimens. Several remarkable findings were obtained. The restoration effects of coal are considerably better than those of sandstone because the strength recovery coefficient of the former is 1.20, whereas that of the latter is 0.33, which indicates that MEYCO 364 is particularly valid for fractured rocks whose initial intact peak stress is less than that of MEYCO 364. Secondary cracked traces of restored sandstone almost follow the cracked traces of the initial intact sandstone, and the final failure is mainly caused by decoupling between the adhesive and the rock mass. However, cracked traces of restored coal only partially follow the traces of intact coal, with the final failure of the restored coal being caused by both bonding interface decoupling and self-breakage in coal. Three-dimensional damage source locations manifest such that AE events are highly correlated with a strength recovery coefficient; the AE events show a decreasing tendency when the coefficient is larger than 1, and vice versa. This study provides a feasible scheme for the reinforcement of fractured rock masses in underground constructions and reveals an internal mechanism of the crushing process for restored rock masses, which has certain instructive significance. PMID:26714324

Development of a quantitative model for the mechanism of raveling failure in highway rock slopes using LIDAR.

DOT National Transportation Integrated Search

2013-03-01

Rock falls on highways while dangerous are unpredictable. Most rock falls are of the raveling type and not conducive to stability : calculations, and even the failure mechanisms are not well understood. LIDAR (LIght Detection And Ranging) has been sh...

The influence of rock strength on erosion processes and river morphology in central Arizona: the accumulation of damage from macro-abrasion

NASA Astrophysics Data System (ADS)

Larimer, J. E.; Yanites, B.

2017-12-01

River morphology reflects the interaction between the driving forces of erosion and the resisting properties of bedrock that limit erosion. Changes in energy dissipation at the riverbed are indicated by differences in channel geometry. To erode at the same rate, stronger rocks require more energy, and thus, an adjustment in river slope or width is necessary to accomplish this work. Therefore, morphological changes should reflect differences in the rock strength properties most relevant to the dominant erosion process. We investigate this hypothesis by comparing river morphology and rock-strength properties of reaches subject to different processes. Streams in Prescott National Forest, AZ expose bedrock through a variety of lithologies, which provides a natural testing ground. Measurements include channel geometry, surface P-wave velocity, fracture spacing, and bedload grain size distribution of 150 individual reaches, as well as 260 tensile and compressive-strength tests and P-wave velocity of cores up to depths of 20 cm. Based on observations, we infer that fluvial erosion processes in this region generally fall into three domains: (1) grain by grain abrasion, (2) progressive failure by damage accumulation due to bedload impacts or `macro-abrasion', and (3) `plucking' of jointed rocks. We focus analyses on the accumulation of damage from sub-critical stresses that weakens the surface of the bedrock, potentially leading to macroscopic fractures, fatigue, and rock failure. This plays a dual role facilitating the ease with which abrasion removes material and increasing the rate of production of pluck-able particles. We estimate the `damage potential' of saltating bedload using water discharge time-series, sediment transport models and grain size distribution. To determine the resistance to damage accumulation among different rocks, we measure the evolution of damage in core samples under uniaxial loading using strain energy and inherent flaw theory. Preliminary results suggest that tensile strength is a good predictor of channel morphology in abrasion dominated reaches, morphology is better predicted through a damage perspective in macro-abrasion dominated reaches, and reduction in P-wave velocity near the surface correlates with damage susceptibility.

Failure Behavior of Granite Affected by Confinement and Water Pressure and Its Influence on the Seepage Behavior by Laboratory Experiments

PubMed Central

Cheng, Cheng; Li, Xiao; Li, Shouding; Zheng, Bo

2017-01-01

Failure behavior of granite material is paramount for host rock stability of geological repositories for high-level waste (HLW) disposal. Failure behavior also affects the seepage behavior related to transportation of radionuclide. Few of the published studies gave a consistent analysis on how confinement and water pressure affect the failure behavior, which in turn influences the seepage behavior of the rock during the damage process. Based on a series of laboratory experiments on NRG01 granite samples cored from Alxa area, a candidate area for China’s HLW disposal, this paper presents some detailed observations and analyses for a better understanding on the failure mechanism and seepage behavior of the samples under different confinements and water pressure. The main findings of this study are as follows: (1) Strength reduction properties were found for the granite under water pressure. Besides, the complete axial stress–strain curves show more obvious yielding process in the pre-peak region and a more gradual stress drop in the post-peak region; (2) Shear fracturing pattern is more likely to form in the granite samples with the effect of water pressure, even under much lower confinements, than the predictions from the conventional triaxial compressive results; (3) Four stages of inflow rate curves are divided and the seepage behaviors are found to depend on the failure behavior affected by the confinement and water pressure. PMID:28773157

High-resolution three-dimensional imaging and analysis of rock falls in Yosemite valley, California

USGS Publications Warehouse

Stock, Gregory M.; Bawden, G.W.; Green, J.K.; Hanson, E.; Downing, G.; Collins, B.D.; Bond, S.; Leslar, M.

2011-01-01

We present quantitative analyses of recent large rock falls in Yosemite Valley, California, using integrated high-resolution imaging techniques. Rock falls commonly occur from the glacially sculpted granitic walls of Yosemite Valley, modifying this iconic landscape but also posing signifi cant potential hazards and risks. Two large rock falls occurred from the cliff beneath Glacier Point in eastern Yosemite Valley on 7 and 8 October 2008, causing minor injuries and damaging structures in a developed area. We used a combination of gigapixel photography, airborne laser scanning (ALS) data, and ground-based terrestrial laser scanning (TLS) data to characterize the rock-fall detachment surface and adjacent cliff area, quantify the rock-fall volume, evaluate the geologic structure that contributed to failure, and assess the likely failure mode. We merged the ALS and TLS data to resolve the complex, vertical to overhanging topography of the Glacier Point area in three dimensions, and integrated these data with gigapixel photographs to fully image the cliff face in high resolution. Three-dimensional analysis of repeat TLS data reveals that the cumulative failure consisted of a near-planar rock slab with a maximum length of 69.0 m, a mean thickness of 2.1 m, a detachment surface area of 2750 m2, and a volume of 5663 ?? 36 m3. Failure occurred along a surfaceparallel, vertically oriented sheeting joint in a clear example of granitic exfoliation. Stress concentration at crack tips likely propagated fractures through the partially attached slab, leading to failure. Our results demonstrate the utility of high-resolution imaging techniques for quantifying far-range (>1 km) rock falls occurring from the largely inaccessible, vertical rock faces of Yosemite Valley, and for providing highly accurate and precise data needed for rock-fall hazard assessment. ?? 2011 Geological Society of America.

Ground thermal and geomechanical conditions in a permafrost-affected high-latitude rock avalanche site (Polvartinden, northern Norway)

NASA Astrophysics Data System (ADS)

Frauenfelder, Regula; Isaksen, Ketil; Lato, Matthew J.; Noetzli, Jeannette

2018-04-01

On 26 June 2008, a rock avalanche detached in the northeast facing slope of Polvartinden, a high-alpine mountain in Signaldalen, northern Norway. Here, we report on the observed and modelled past and present near-surface temperature regime close to the failure zone, as well as on a subsequent simulation of the subsurface temperature regime, and on initial geomechanical mapping based on laser scanning. The volume of the rock avalanche was estimated to be approximately 500 000 m3. The depth to the actual failure surface was found to range from 40 m at the back of the failure zone to 0 m at its toe. Visible in situ ice was observed in the failure zone just after the rock avalanche. Between September 2009 and August 2013, ground surface temperatures were measured with miniature temperature data loggers at 14 different localities, close to the original failure zone along the northern ridge of Polvartinden and on the valley floor. The results from these measurements and from a basic three-dimensional heat conduction model suggest that the lower altitudinal limit of permafrost at present is at 600-650 m a.s.l., which corresponds to the upper limit of the failure zone. A coupling of our in situ data with regional climate data since 1958 suggests a general gradual warming and that the period with highest mean near surface temperatures on record ended four months before the Signaldalen rock avalanche detached. A comparison with a transient permafrost model run at 10 m depth, representative for areas where snow accumulates, strengthen these findings, which are also in congruence with measurements in nearby permafrost boreholes. It is likely that permafrost in and near the failure zone is presently subject to degradation. This degradation, in combination with the extreme warm year antecedent to the rock failure, is seen to have played an important role in the detaching of the Signaldalen rock avalanche.

Acoustic Emission Characteristics of Red Sandstone Specimens Under Uniaxial Cyclic Loading and Unloading Compression

NASA Astrophysics Data System (ADS)

Meng, Qingbin; Zhang, Mingwei; Han, Lijun; Pu, Hai; Chen, Yanlong

2018-04-01

To explore the acoustic emission (AE) characteristics of rock materials during the deformation and failure process under periodic loads, a uniaxial cyclic loading and unloading compression experiment was conducted based on an MTS 815 rock mechanics test system and an AE21C acoustic emissions test system. The relationships among stress, strain, AE activity, accumulated AE activity and duration for 180 rock specimens under 36 loading and unloading rates were established. The cyclic AE evolutionary laws with rock stress-strain variation at loading and unloading stages were analyzed. The Kaiser and Felicity effects of rock AE activity were disclosed, and the impact of the significant increase in the scale of AE events on the Felicity effect was discussed. It was observed that the AE characteristics are closely related to the stress-strain properties of rock materials and that they are affected by the developmental state and degree of internal microcracks. AE events occur in either the loading or unloading stages if the strain is greater than zero. Evolutionary laws of AE activity agree with changes in rock strain. Strain deformation is accompanied by AE activity, and the density and intensity of AE events directly reflect the damage degree of the rock mass. The Kaiser effect exists in the linear elastic stage of rock material, and the Felicity effect is effective in the plastic yield and post-peak failure stages, which are divided by the elastic yield strength. This study suggests that the stress level needed to determine a significant increase in AE activity was 70% of the i + 1 peak stress. The Felicity ratio of rock specimens decreases with the growth of loading-unloading cycles. The cycle magnitude and variation of the Felicity effect, in which loading and unloading rates play a weak role, are almost consistent.

Design of Rock Slope Reinforcement: An Himalayan Case Study

NASA Astrophysics Data System (ADS)

Tiwari, Gaurav; Latha, Gali Madhavi

2016-06-01

The stability analysis of the two abutment slopes of a railway bridge proposed at about 359 m above the ground level, crossing a river and connecting two hill faces in the Himalayas, India, is presented. The bridge is located in a zone of high seismic activity. The rock slopes are composed of a heavily jointed rock mass and the spacing, dip and dip direction of joint sets are varying at different locations. Geological mapping was carried out to characterize all discontinuities present along the slopes. Laboratory and field investigations were conducted to assess the geotechnical properties of the intact rock, rock mass and joint infill. Stability analyses of these rock slopes were carried out using numerical programmes. Loads from the foundations resting on the slopes and seismic accelerations estimated from site-specific ground response analysis were considered. The proposed slope profile with several berms between successive foundations was simulated in the numerical model. An equivalent continuum approach with Hoek and Brown failure criterion was initially used in a finite element model to assess the global stability of the slope abutments. In the second stage, finite element analysis of rock slopes with all joint sets with their orientations, spacing and properties explicitly incorporated into the numerical model was taken up using continuum with joints approach. It was observed that the continuum with joints approach was able to capture the local failures in some of the slope sections, which were verified using wedge failure analysis and stereographic projections. Based on the slope deformations and failure patterns observed from the numerical analyses, rock anchors were designed to achieve the target factors of safety against failure while keeping the deformations within the permissible limits. Detailed design of rock anchors and comparison of the stability of slopes with and without reinforcement are presented.

Crack propagation and coalescence due to dual non-penetrating surface flaws and their effect on the strength of rock-like material

NASA Astrophysics Data System (ADS)

Xu, Jun; Zheng, Zheyuan; Xiao, Xiaochun; Li, Zhaoxia

2018-06-01

Non-penetrating surface flaws play a key role in the fracture process of rock-like material, and could cause localized collapse and even failure of the materials. Until now, the mechanism and the effect of surface crack propagation have remained unclear. In this paper, compression tests on gypsum (a soft rock material) are conducted to investigate crack propagation and coalescence due to non-penetrating surface flaws and their effect on the material strength. Specimens are tested under dual pre-existing surface flaws with various combinations of depth and spacing. The results show that when the pre-existing flaws are non-penetrating, the d/t ratio (flaw depth ratio, d is the pre-existing flaw cutting depth and t is the specimen thickness) and the spacing (the distance between the two flaw internal tips) have a strong influence on surface crack patterns and specimen strength. Few cracks emanate from the pre-existing flaws when the flaw depth ratio is equal to 1/3, and more cracks occur with the increase of the flaw depth ratio. When the pre-existing flaw penetrates completely through the specimen, the spacing has a small effect on the specimen strength. A larger flaw depth ratio could advance the occurrence of the peak load (PL) and result in a smaller specimen residual strength. The failure process of the specimen is divided into several stages featured by a stepped decline of the load value after PL, which is closely related to the initiation and propagation of secondary cracks. In addition, the spalling (failure of a portion of the surface caused by coalescence of cracks) can be regarded as indicating the failure of the specimen, and two possible types of spalling formation are briefly discussed.

A 3D Analysis of Rock Block Deformation and Failure Mechanics Using Terrestrial Laser Scanning

NASA Astrophysics Data System (ADS)

Rowe, Emily; Hutchinson, D. Jean; Kromer, Ryan A.; Edwards, Tom

2017-04-01

Many natural geological hazards are present along the Thompson River corridor in British Columbia, Canada, including one particularly hazardous rocky slope known as the White Canyon. Railway tracks used by Canadian National (CN) and Canadian Pacific (CP) Railway companies pass through this area at the base of the Canyon slope. The geologically complex and weathered rock face exposed at White Canyon is prone to rockfalls. With a limited ditch capacity, these falling rocks have the potential to land on the tracks and therefore increase the risk of train derailment. Since 2012, terrestrial laser scanning (TLS) data has been collected at this site on a regular basis to enable researchers at Queen's University to study these rockfalls in greater detail. In this paper, the authors present a summary of an analysis of these TLS datasets including an examination of the pre-failure deformation patterns exhibited by failed rock blocks as well as an investigation into the influence of structural constraints on the pre-failure behavior of these blocks. Aligning rockfall source zones in an early point cloud dataset to a later dataset generates a transformation matrix describing the movement of the block from one scan to the next. This process was repeated such that the motion of the block over the entire TLS data coverage period was measured. A 3D roto-translation algorithm was then used to resolve the motion into translation and rotation components (Oppikofer et al. 2009; Kromer et al. 2015). Structural information was plotted on a stereonet for further analysis. A total of 111 rockfall events exceeding a volume of 1 m3 were analyzed using this approach. The study reveals that although some rockfall source blocks blocks do not exhibit detectable levels of deformation prior to failure, others do experience cm-level translation and rotation on the order of 1 to 6 degrees before detaching from the slope. Moreover, these movements may, in some cases, be related to the discontinuity planes on the slope that were confining the block. It is concluded that rock blocks in White Canyon may be classified as one of five main failure mechanisms based on their pre-failure deformation and structure: planar slide, topple, rotation, wedge, and overhang, with overhang failures representing a large portion of rockfalls in this area. Overhang rockfalls in the White Canyon are characterized by blocks that (a) are not supported by an underlying discontinuity plane, and (b) generally do not exhibit pre-failure deformation. Though overhanging rock blocks are a structural subset of toppling failure, their behavior suggests a different mechanism of detachment. Future work will further populate the present database of rockfalls in White Canyon and will expand the study to include other sites along this corridor. The ultimate goal of this research is to establish warning thresholds based on deformation magnitudes for rockfalls in White Canyon to assist Canadian railways in better understanding and managing these slopes.

Geomechanical Characterization and Stability Analysis of the Bedrock Underlying the Costa Concordia Cruise Ship

NASA Astrophysics Data System (ADS)

Dotta, Giulia; Gigli, Giovanni; Ferrigno, Federica; Gabbani, Giuliano; Nocentini, Massimiliano; Lombardi, Luca; Agostini, Andrea; Nolesini, Teresa; Casagli, Nicola

2017-09-01

The shipwreck of the Costa Concordia cruise ship, which ran aground on 13 January 2012 on the northwestern coast of Giglio Island (Italy), required continuous monitoring of the position and movement of the vessel to guarantee the security of workers and rescuers operating around and within the wreck and to support shipwreck removal operations. Furthermore, understanding the geomechanical properties and stability behaviour of the coastal rock mass and rocky seabed underlying the ship was of similar importance. To assess the stability conditions of the ship, a ground-based monitoring system was installed in front of the wreck. The network included a terrestrial laser scanner (TLS) device, which was used to perform remote semiautomatic geomechanical characterization of the observed rock mass. Using TLS survey techniques, three main discontinuity sets were identified in the granitic rock mass of Giglio Island. Furthermore, a multibeam bathymetric survey was used to qualitatively characterize the seabed. To integrate the processed TLS data and quantitatively describe the rock mass quality, a subsequent field survey was carried out to provide a rock mass geomechanical evaluation (from very good to moderate quality). Based on the acquired information, kinematic and stability analyses were performed to create a spatial prediction of rock failure mechanisms in the study area. The obtained kinematic hazard index values were generally low; only the plane failure index reached slightly higher values. The general stability of the rock mass was confirmed by the stability analysis, which yielded a high safety factor value (approximately 12).

The influence of thermal and cyclic stressing on the strength of rocks from Mount St. Helens, Washington

NASA Astrophysics Data System (ADS)

Kendrick, Jackie Evan; Smith, Rosanna; Sammonds, Peter; Meredith, Philip G.; Dainty, Matthew; Pallister, John S.

2013-07-01

Stratovolcanoes and lava domes are particularly susceptible to sector collapse resulting from wholesale rock failure as a consequence of decreasing rock strength. Here, we provide insights into the influence of thermal and cyclic stressing on the strength and mechanical properties of volcanic rocks. Specifically, this laboratory study examines the properties of samples from Mount St. Helens; chosen because its strength and stability have played a key role in its history, influencing the character of the infamous 1980 eruption. We find that thermal stressing exerts different effects on the strengths of different volcanic units; increasing the heterogeneity of rocks in situ. Increasing the uniaxial compressive stress generates cracking, the timing and magnitude of which was monitored via acoustic emission (AE) output during our experiments. AEs accelerated in the approach to failure, sometimes following the pattern predicted by the failure forecast method (Kilburn 2003). Crack damage during the experiments was tracked using the evolving static Young's modulus and Poisson's ratio, which represent the quasi-static deformation in volcanic edifices more accurately than dynamic elastic moduli which are usually implemented in volcanic models. Cyclic loading of these rocks resulted in a lower failure strength, confirming that volcanic rocks may be weakened by repeated inflation and deflation of the volcanic edifice. Additionally, volcanic rocks in this study undergo significant elastic hysteresis; in some instances, a material may fail at a stress lower than the peak stress which has previously been endured. Thus, a volcanic dome repeatedly inflated and deflated may progressively weaken, possibly inducing failure without necessarily exceeding earlier conditions.

Insights on surface spalling of rock

NASA Astrophysics Data System (ADS)

Tarokh, Ali; Kao, Chu-Shu; Fakhimi, Ali; Labuz, Joseph F.

2016-07-01

Surface spalling is a complex failure phenomenon that features crack propagation and detachment of thin pieces of rock near free surfaces, particularly in brittle rock around underground excavations when large in situ stresses are involved. A surface instability apparatus was used to study failure of rock close to a free surface, and damage evolution was monitored by digital image correlation (DIC). Lateral displacement at the free face was used as the feedback signal to control the post-peak response of the specimen. DIC was implemented in order to obtain the incremental displacement fields during the spalling process. Displacement fields were computed in the early stage of loading as well as close to the peak stress. Fracture from the spalling phenomenon was revealed by incremental lateral displacement contours. The axial and lateral displacements suggested that the displacement gradient was uniform in both directions at early loading stages and as the load increased, the free-face effect started to influence the displacements, especially the lateral displacement field. A numerical approach, based on the discrete element method, was developed and validated from element testing. Damage evolution and localization observed in numerical simulations were similar to those observed in experiments. By performing simulations in two- and three-dimensions, it was revealed that the intermediate principal stress and platen-rock interfaces have important effects on simulation of surface spalling.

Shallow near-fault material self organizes so it is just nonlinear in typical strong shaking

NASA Astrophysics Data System (ADS)

Sleep, N. H.

2011-12-01

Cracking within shallow compliant fault zones self-organizes so that strong dynamic stresses marginally exceed the elastic limit. To the first order, the compliant material experiences strain boundary conditions imposed by underlying stiffer rock. A major strike-slip fault yields simple dimensional relations. The near-field velocity pulse is essentially a Love wave. The dynamic strain is the ratio of the measured particle velocity over the deep S-wave velocity. The shallow dynamic stress is this quantity times the local shear modulus. I obtain the equilibrium shear modulus by starting a sequence of earthquakes with intact stiff rock surrounding the shallow fault zone. The imposed dynamic strain in stiff rock causes Coulomb failure and leaves cracks in it wake. Cracked rock is more compliant than the original intact rock. Each subsequent event causes more cracking until the rock becomes compliant enough that it just reaches its elastic limit. Further events maintain the material at the shear modulus where it just fails. Analogously, shallow damaged regolith forms with its shear modulus and S-wave velocity increasing with depth so it just reaches failure during typical strong shaking. The general conclusion is that shallow rocks in seismically active areas just become nonlinear during typical shaking. This process causes transient changes in S-wave velocity, but not strong nonlinear attenuation of seismic waves. Wave amplitudes significantly larger than typical ones would strongly attenuate and strongly damage the rock. The equilibrium shear modulus and S-wave velocity depend only modestly on the effective coefficient of internal friction.

Experimental Investigation on the Fatigue Mechanical Properties of Intermittently Jointed Rock Models Under Cyclic Uniaxial Compression with Different Loading Parameters

NASA Astrophysics Data System (ADS)

Liu, Yi; Dai, Feng; Dong, Lu; Xu, Nuwen; Feng, Peng

2018-01-01

Intermittently jointed rocks, widely existing in many mining and civil engineering structures, are quite susceptible to cyclic loading. Understanding the fatigue mechanism of jointed rocks is vital to the rational design and the long-term stability analysis of rock structures. In this study, the fatigue mechanical properties of synthetic jointed rock models under different cyclic conditions are systematically investigated in the laboratory, including four loading frequencies, four maximum stresses, and four amplitudes. Our experimental results reveal the influence of the three cyclic loading parameters on the mechanical properties of jointed rock models, regarding the fatigue deformation characteristics, the fatigue energy and damage evolution, and the fatigue failure and progressive failure behavior. Under lower loading frequency or higher maximum stress and amplitude, the jointed specimen is characterized by higher fatigue deformation moduli and higher dissipated hysteresis energy, resulting in higher cumulative damage and lower fatigue life. However, the fatigue failure modes of jointed specimens are independent of cyclic loading parameters; all tested jointed specimens exhibit a prominent tensile splitting failure mode. Three different crack coalescence patterns are classified between two adjacent joints. Furthermore, different from the progressive failure under static monotonic loading, the jointed rock specimens under cyclic compression fail more abruptly without evident preceding signs. The tensile cracks on the front surface of jointed specimens always initiate from the joint tips and then propagate at a certain angle with the joints toward the direction of maximum compression.

Analysis of Tsunamigenic Coastal Rock Slope Failures Triggered by the 2007 Earthquake in the Chilean Fjordland

NASA Astrophysics Data System (ADS)

Sepulveda, S. A.; Serey, A.; Hermanns, R. L.; Redfield, T. F.; Oppikofer, T.; Duhart, P.

2011-12-01

The fjordland of the Chilean Patagonia is subject to active tectonics, with large magnitude subduction earthquakes, such as the M 9.5 1960 earthquake, and shallow crustal earthquakes along the regional Liquiñe-Ofqui Fault Zone (LOFZ). One of the latter (M 6.2) struck the Aysen Fjord region (45.5 S) on the 21st of April 2007, triggering dozens of landslides in the epicentral area along the fjord coast and surroundings. The largest rock slides and rock avalanches induced a local tsunami that together with debris flows caused ten fatalities and severely damaged several salmon farms, the most important economic activity of the area. Multi-scale studies of the landslides triggered during the Aysen earthquake have been carried out, including landslide mapping and classification, slope stability back-analyses and structural and geomorphological mapping of the largest failures from field surveys and high-resolution digital surface models created from terrestrial laser scanning. The failures included rock slides, rock avalanches, rock-soil slides, soil slides and debris flows. The largest rock avalanche had a volume of over 20 million cubic metres. The landslides affected steep slopes of intrusive rocks of the North Patagonian batholith covered by a thin layer of volcanic soils, which supports a high forest. The results of geotechnical analyses suggest a site effect due to topographic amplification on the generation of the landslides, with peak ground accelerations that may have reached between about 1.0 and 2.0 g for rock avalanches and between 0.6 and 1.0 g for shallow rock-soil slides, depending on the amount of assumed vertical acceleration and the applied method (limit equilibrium and Newmark). Attenuation relationships for shallow crustal seismicity indicate accelerations below 0.5 g for earthquakes of a similar magnitude and epicentral distances. Detailed field structural analyses of the largest rock avalanche in Punta Cola indicate a key role in the failure mechanics of brittle faults and jointing related to the LOFZ. The basal failure plane closely followed an older (epidote chlorite facies) thrust fault. Later fracture patterns suggest the thrust relaxed under gravitational stress following rock column uplift. Failure probably utilized a combination of these structures. Digital geomorphic models allowed establishing a sequence of events during failure which together make up the complex rock avalanche deposit. The volume of each individual slide could be more accurately determined. These and ongoing studies will allow a unique characterization of earthquake-induced slope failures in fjord coastal environments, providing new tools for landslide, seismic and tsunami hazard assessment in Patagonia and similar geomorphological settings around the world. This work was funded by Fondecyt project 11070107, the International Center for Geohazards, the Millenium Nucleus 'International Earthquake Research Center Montessus de Ballore', FNDR-Project 'Geological-Mining Environmental Research in Aysen' of the Chilean Government and the Andean Geothermal Center of Excellence.

Time-dependent deformation at elevated temperatures in basalt from El Hierro, Stromboli and Teide volcanoes

NASA Astrophysics Data System (ADS)

Benson, P. M.; Fahrner, D.; Harnett, C. E.; Fazio, M.

2014-12-01

Time dependent deformation describes the process whereby brittle materials deform at a stress level below their short-term material strength (Ss), but over an extended time frame. Although generally well understood in engineering (where it is known as static fatigue or "creep"), knowledge of how rocks creep and fail has wide ramifications in areas as diverse as mine tunnel supports and the long term stability of critically loaded rock slopes. A particular hazard relates to the instability of volcano flanks. A large number of flank collapses are known such as Stromboli (Aeolian islands), Teide, and El Hierro (Canary Islands). Collapses on volcanic islands are especially complex as they necessarily involve the combination of active tectonics, heat, and fluids. Not only does the volcanic system generate stresses that reach close to the failure strength of the rocks involved, but when combined with active pore fluid the process of stress corrosion allows the rock mass to deform and creep at stresses far lower than Ss. Despite the obvious geological hazard that edifice failure poses, the phenomenon of creep in volcanic rocks at elevated temperatures has yet to be thoroughly investigated in a well controlled laboratory setting. We present new data using rocks taken from Stromboli, El Heirro and Teide volcanoes in order to better understand the interplay between the fundamental rock mechanics of these basalts and the effects of elevated temperature fluids (activating stress corrosion mechanisms). Experiments were conducted over short (30-60 minute) and long (8-10 hour) time scales. For this, we use the method of Heap et al., (2011) to impose a constant stress (creep) domain deformation monitored via non-contact axial displacement transducers. This is achieved via a conventional triaxial cell to impose shallow conditions of pressure (<25 MPa) and temperature (<200 °C), and equipped with a 3D laboratory seismicity array (known as acoustic emission, AE) to monitor the micro cracking due to the imposed deformation. By measuring the AE generated during deformation we are then able to apply fracture forecast models to predict, retrospectively, the time of failure. We find that higher temperatures increase the strain rate during creep for the same %Ss, and that the accuracy of the forecast does not change with increasing temperature.

Transverse Isotropy of Phyllite Under Brazilian Tests: Laboratory Testing and Numerical Simulations

NASA Astrophysics Data System (ADS)

Xu, Guowen; He, Chuan; Chen, Ziquan; Su, Ang

2018-04-01

Phyllite is a low-grade, metamorphic rock with well-developed foliation. We characterized the fracture pattern and failure strength of phyllite specimens under Brazilian tests. The specimens were obtained from the Zhegu mountain tunnel in China and had different foliation-loading angles, namely 0°, 15°, 30°, 45°, 60°, 75° and 90°. The processes for the initiation and propagation of macro-cracks were recorded using high-speed photography. The evolution of micro-cracks was analyzed based on the results of acoustic emission (AE) tests. The failure process of the specimens during the Brazilian tests was simulated with a new numerical approach based on the particle discrete element method. The influence of foliation strength and the microstructure of the rock matrix were also studied numerically. The experimental results showed that the failure strength of the specimens was related to their fracture patterns and the areas of their fracture surfaces. The initial cracking point of the specimens appeared at the upper or lower loading position, and the cracks propagated to the boundaries of the specimens along or across foliation. The temporal distributions of the AE counts and AE energy of the specimens were affected predominantly by the fracture pattern, and we divided these distributions into two modes: the peak mode and the uniformly distributed mode. The numerical results indicated that the fracture surface was roughly parallel to the loading direction and that the surface was located in the central part of the disk specimens for rocks with loose structure (low coordination number or large crack density) or with strong foliation, i.e., foliation with high shear strength. The failure pattern and trends of variation in failure strength as a function of foliation-loading angles varied with the ratio of cohesion to the tensile strength of foliation, the crack density, and the coordination number.

Fracture Reactivation in Chemically Reactive Rock Systems

NASA Astrophysics Data System (ADS)

Eichhubl, P.; Hooker, J. N.

2013-12-01

Reactivation of existing fractures is a fundamental process of brittle failure that controls the nucleation of earthquake ruptures, propagation and linkage of hydraulic fractures in oil and gas production, and the evolution of fault and fracture networks and thus of fluid and heat transport in the upper crust. At depths below 2-3 km, and frequently shallower, brittle processes of fracture growth, linkage, and reactivation compete with chemical processes of fracture sealing by mineral precipitation, with precipitation rates similar to fracture opening rates. We recently found rates of fracture opening in tectonically quiescent settings of 10-20 μm/m.y., rates similar to euhedral quartz precipitation under these conditions. The tendency of existing partially or completely cemented fractures to reactivate will vary depending on strain rate, mineral precipitation kinetics, strength contrast between host rock and fracture cement, stress conditions, degree of fracture infill, and fracture network geometry. Natural fractures in quartzite of the Cambrian Eriboll Formation, NW Scotland, exhibit a complex history of fracture formation and reactivation, with reactivation involving both repeated crack-seal opening-mode failure and shear failure of fractures that formed in opening mode. Fractures are partially to completely sealed with crack-seal or euhedral quartz cement or quartz cement fragmented by shear reactivation. Degree of cementation controls the tendency of fractures for later shear reactivation, to interact elastically with adjacent open fractures, and their intersection behavior. Using kinematic, dynamic, and diagenetic criteria, we determine the sequence of opening-mode fracture formation and later shear reactivation. We find that sheared fracture systems of similar orientation display spatially varying sense of slip We attribute these inconsistent directions of shear reactivation to 1) a heterogeneous stress field in this highly fractured rock unit and 2) variations in the degree of fracture cement infill in fractures of same orientation, allowing fractures to reactivate at times when adjacent, more cemented fractures remain dormant. The observed interaction of chemical and mechanical fracture growth and sealing processes in this chemically reactive and heavily deformed rock unit results in a complex fracture network geometry not generally observed in less chemically reactive, shallower crustal environments.

Subcritical crack growth and other time- and environment-dependent behavior in crustal rocks

NASA Technical Reports Server (NTRS)

Swanson, P. L.

1984-01-01

Stable crack growth strongly influences both the fracture strength of brittle rocks and some of the phenomena precursory to catastrophic failure. Quantification of the time and environment dependence of fracture propagation is attempted with the use of a fracture mechanics technique. Some of the difficulties encountered when applying techniques originally developed for simple synthetic materials to complex materials like rocks are examined. A picture of subcritical fracture propagation is developed that embraces the essential ingredients of the microstructure, a microcrack process zone, and the different roles that the environment plays. To do this, the results of (1) fracture mechanics experiments on five rock types, (2) optical and scanning electron microscopy, (3) studies of microstructural aspects of fracture in ceramics, and (4) exploratory tests examining the time-dependent response of rock to the application of water are examined.

Similar simulation study on the characteristics of the electric potential response to coal mining

NASA Astrophysics Data System (ADS)

Niu, Yue; Li, Zhonghui; Kong, Biao; Wang, Enyuan; Lou, Quan; Qiu, Liming; Kong, Xiangguo; Wang, Jiali; Dong, Mingfu; Li, Baolin

2018-02-01

An electric potential (EP) can be generated during the failure process of coal and rock. In this article, a similar physical model of coal rock was built and the characteristics of the EP responding to the process of coal mining were studied. The results showed that, at the early mining stage, the structure of coal rock strata were stable in the simulation model, the support stress of overlying coal rock strata was low and the maximum subsidence was little, while the EP change was less. With the advancement of the working face, the support stress of the overlying coal rock strata in the mined-out area changed dramatically, the maximum subsidence increased constantly, the deformation and destruction were aggravated, and cracks expanded continuously. Meanwhile, the EP response was significant with fluctuation. When significant macro damage appeared in coal rock strata, the EP signal fluctuation was violent. The overlying coal rock strata were influenced by gravity and mining activity. During the mining process, the crack growth and the friction, together with slip between coal and rock particles, resulted in the response of EP. The change in EP was closely related to the damage state and stress distribution of the coal rock strata. EP monitoring has the advantages of accurate reflection and strong anti-interference in the field. Therefore, with further study, an EP monitoring method could be applied for monitoring and early warning of coal and rock dynamic disaster, and risk evaluation in the future. The strength of the EP and its fluctuation degree could serve as the key discrimination indexes.

In Situ Observation of Rock Spalling in the Deep Tunnels of the China Jinping Underground Laboratory (2400 m Depth)

NASA Astrophysics Data System (ADS)

Feng, Xia-Ting; Xu, Hong; Qiu, Shi-Li; Li, Shao-Jun; Yang, Cheng-Xiang; Guo, Hao-Sen; Cheng, Yuan; Gao, Yao-Hui

2018-04-01

To study rock spalling in deep tunnels at China Jinping Underground Laboratory Phase II (CJPL-II), photogrammetry method and digital borehole camera were used to quantify key features of rock spalling including orientation, thickness of slabs and the depth of spalling. The failure mechanism was analysed through scanning electron microscope and numerical simulation based on FLAC3D. Observation results clearly showed the process of rock spalling failure: a typical spalling pattern around D-shaped tunnels after top-heading and bottom bench were discovered. The orientation and thickness of the slabs were obtained. The slabs were parallel to the excavated surfaces of the tunnel and were related to the shape of the tunnel surface and orientation of the principal stress. The slabs were alternately thick and thin, and they gradually increased in thickness from the sidewall inwards. The form and mechanism of spalling at different locations in the tunnels, as influenced by stress state and excavation, were analysed. The result of this study was helpful to those rethinking the engineering design, including the excavation and support of tunnels, or caverns, at high risk of spalling.

Discrete Analysis of Damage and Shear Banding in Argillaceous Rocks

NASA Astrophysics Data System (ADS)

Dinç, Özge; Scholtès, Luc

2018-05-01

A discrete approach is proposed to study damage and failure processes taking place in argillaceous rocks which present a transversely isotropic behavior. More precisely, a dedicated discrete element method is utilized to provide a micromechanical description of the mechanisms involved. The purpose of the study is twofold: (1) presenting a three-dimensional discrete element model able to simulate the anisotropic macro-mechanical behavior of the Callovo-Oxfordian claystone as a particular case of argillaceous rocks; (2) studying how progressive failure develops in such material. Material anisotropy is explicitly taken into account in the numerical model through the introduction of weakness planes distributed at the interparticle scale following predefined orientation and intensity. Simulations of compression tests under plane-strain and triaxial conditions are performed to clarify the development of damage and the appearance of shear bands through micromechanical analyses. The overall mechanical behavior and shear banding patterns predicted by the numerical model are in good agreement with respect to experimental observations. Both tensile and shear microcracks emerging from the modeling also present characteristics compatible with microstructural observations. The numerical results confirm that the global failure of argillaceous rocks is well correlated with the mechanisms taking place at the local scale. Specifically, strain localization is shown to directly result from shear microcracking developing with a preferential orientation distribution related to the orientation of the shear band. In addition, localization events presenting characteristics similar to shear bands are observed from the early stages of the loading and might thus be considered as precursors of strain localization.

DaDyn-RS: a tool for the time-dependent simulation of damage, fluid pressure and long-term instability in alpine rock slopes

NASA Astrophysics Data System (ADS)

Riva, Federico; Agliardi, Federico; Amitrano, David; Crosta, Giovanni B.

2017-04-01

Large mountain slopes in alpine environments undergo a complex long-term evolution from glacial to postglacial environments, through a transient period of paraglacial readjustment. During and after this transition, the interplay among rock strength, topographic relief, and morpho-climatic drivers varying in space and time can lead to the development of different types of slope instability, from sudden catastrophic failures to large, slow, long-lasting yet potentially catastrophic rockslides. Understanding the long-term evolution of large rock slopes requires accounting for the time-dependence of deglaciation unloading, permeability and fluid pressure distribution, displacements and failure mechanisms. In turn, this is related to a convincing description of rock mass damage processes and to their transition from a sub-critical (progressive failure) to a critical (catastrophic failure) character. Although mechanisms of damage occurrence in rocks have been extensively studied in the laboratory, the description of time-dependent damage under gravitational load and variable external actions remains difficult. In this perspective, starting from a time-dependent model conceived for laboratory rock deformation, we developed Dadyn-RS, a tool to simulate the long-term evolution of real, large rock slopes. Dadyn-RS is a 2D, FEM model programmed in Matlab, which combines damage and time-to-failure laws to reproduce both diffused damage and strain localization meanwhile tracking long-term slope displacements from primary to tertiary creep stages. We implemented in the model the ability to account for rock mass heterogeneity and property upscaling, time-dependent deglaciation, as well as damage-dependent fluid pressure occurrence and stress corrosion. We first tested DaDyn-RS performance on synthetic case studies, to investigate the effect of the different model parameters on the mechanisms and timing of long-term slope behavior. The model reproduces complex interactions between topography, deglaciation rate, mechanical properties and fluid pressure occurrence, resulting in different kinematics, damage patterns and timing of slope instabilities. We assessed the role of groundwater on slope damage and deformation mechanisms by introducing time-dependent pressure cycling within simulations. Then, we applied DaDyn-RS to real slopes located in the Italian Central Alps, affected by an active rockslide and a Deep Seated Gravitational Slope Deformation, respectively. From Last Glacial Maximum to present conditions, our model allows reproducing in an explicitly time-dependent framework the progressive development of damage-induced permeability, strain localization and shear band differentiation at different times between the Lateglacial period and the Mid-Holocene climatic transition. Different mechanisms and timings characterize different styles of slope deformations, consistently with available dating constraints. DaDyn-RS is able to account for different long-term slope dynamics, from slow creep to the delayed transition to fast-moving rockslides.

An experimental study on fracture mechanical behavior of rock-like materials containing two unparallel fissures under uniaxial compression

NASA Astrophysics Data System (ADS)

Huang, Yan-Hua; Yang, Sheng-Qi; Tian, Wen-Ling; Zeng, Wei; Yu, Li-Yuan

2016-06-01

Strength and deformability characteristics of rock with pre-existing fissures are governed by cracking behavior. To further research the effects of pre-existing fissures on the mechanical properties and crack coalescence process, a series of uniaxial compression tests were carried out for rock-like material with two unparallel fissures. In the present study, cement, quartz sand, and water were used to fabricate a kind of brittle rock-like material cylindrical model specimen. The mechanical properties of rock-like material specimen used in this research were all in good agreement with the brittle rock materials. Two unparallel fissures (a horizontal fissure and an inclined fissure) were created by inserting steel during molding the model specimen. Then all the pre-fissured rock-like specimens were tested under uniaxial compression by a rock mechanics servo-controlled testing system. The peak strength and Young's modulus of pre-fissured specimen all first decreased and then increased when the fissure angle increased from 0° to 75°. In order to investigate the crack initiation, propagation and coalescence process, photographic monitoring was adopted to capture images during the entire deformation process. Moreover, acoustic emission (AE) monitoring technique was also used to obtain the AE evolution characteristic of pre-fissured specimen. The relationship between axial stress, AE events, and the crack coalescence process was set up: when a new crack was initiated or a crack coalescence occurred, the corresponding axial stress dropped in the axial stress-time curve and a big AE event could be observed simultaneously. Finally, the mechanism of crack propagation under microscopic observation was discussed. These experimental results are expected to increase the understanding of the strength failure behavior and the cracking mechanism of rock containing unparallel fissures.

Rheological model analysis on depth of toppling deformation in the anti-dip rock slope

NASA Astrophysics Data System (ADS)

Zheng, Da

2017-04-01

The failure of the toppling deformation occurred in the layered rock mass, it is a kind of mode of deformation and failure, which is bent towards free direction and gradually develops into the slope under the combined forces of in-situ stress, gravity, and groundwater dynamic (hydrostatic) pressure and so on. The most common toppling deformation is the toppling of ductile bending. Obtaining the developmental depth of bending deformation is of great significance for judging the development scale of the plasmodium and the stability of the slope. At present, the developmental depth of toppling deformation mainly depends on the survey and statistic of the exploration adit, or the simulation of the deformation and failure process through the numerical simulation method, there is little research on the developmental depth of toppling deformation from mechanics point of view. In this paper, with the consideration of the time-sensitive characteristics of developmental process of the toppling deformation, the anti-dip layered slope can be considered as a multi-layer superposition cantilever with fixed end and free end, bending under self-weight and inter-layer stress. Under the premise of the initial stage of rheology of the rock slopes, which is considered to be the limit position of the toppling deformation and development, the Kelvin rheological model, which is usually used to describe the decay creep, is chosen to describe the time-sensitive process of rock slopes. The stress-strain analysis calculation is used to obtain the time-varying expression of a certain point on the rock beam. Furthermore, taking the time to infinity, the depth of the layered rock slopes is calculated as x=4Ccosβ/[2γcosαcosβ - γ2(cos (α + β)+2sin(α + β)tanφ)*((1+n) /2+(1-n) cos2α/ 2)] , which is obtained by using the strain reaches zero as the criterion of the depth at toppling deformation development limit position, combining the time-varying expression of a certain point on the beam. we obtain the mathematic analysis conditions by using the constant positive characteristic of depth of the toppling deformation, The result shows that the depth of the slope toppling deformation is influenced by the rock mass, strata inclination, rock thickness, interfacial friction coefficient, interlayer internal friction angle, slope angel and Poisson 's ratio of rock slopes. The toppling deformation only occurs when 2cosαcosβ-[cos(α + β)+2sin(α + β)tanφ][(1+n)/2+(1-n) cos2α/2]≥0. This study is an exploration to explain the time-sensitive characteristics of toppling deformation by using rheological theory. The conclusion is of great significance for the study of the location of the bending zone, the size of the toppling deformation, the stability analysis and the early identification of the toppling deformation based on the deformation characteristics.

Active and passive seismic methods for characterization and monitoring of unstable rock masses: field surveys, laboratory tests and modeling.

NASA Astrophysics Data System (ADS)

Colombero, Chiara; Baillet, Laurent; Comina, Cesare; Jongmans, Denis; Vinciguerra, Sergio

2016-04-01

Appropriate characterization and monitoring of potentially unstable rock masses may provide a better knowledge of the active processes and help to forecast the evolution to failure. Among the available geophysical methods, active seismic surveys are often suitable to infer the internal structure and the fracturing conditions of the unstable body. For monitoring purposes, although remote-sensing techniques and in-situ geotechnical measurements are successfully tested on landslides, they may not be suitable to early forecast sudden rapid rockslides. Passive seismic monitoring can help for this purpose. Detection, classification and localization of microseismic events within the prone-to-fall rock mass can provide information about the incipient failure of internal rock bridges. Acceleration to failure can be detected from an increasing microseismic event rate. The latter can be compared with meteorological data to understand the external factors controlling stability. On the other hand, seismic noise recorded on prone-to-fall rock slopes shows that the temporal variations in spectral content and correlation of ambient vibrations can be related to both reversible and irreversible changes within the rock mass. We present the results of the active and passive seismic data acquired at the potentially unstable granitic cliff of Madonna del Sasso (NW Italy). Down-hole tests, surface refraction and cross-hole tomography were carried out for the characterization of the fracturing state of the site. Field surveys were implemented with laboratory determination of physico-mechanical properties on rock samples and measurements of the ultrasonic pulse velocity. This multi-scale approach led to a lithological interpretation of the seismic velocity field obtained at the site and to a systematic correlation of the measured velocities with physical properties (density and porosity) and macroscopic features of the granitic cliff (fracturing, weathering and anisotropy). Continuous passive seismic monitoring at the site, from October 2013 to present, systematically highlighted clear energy peaks in the spectral content of seismic noise on the unstable sector, interpreted as resonant frequencies of the investigated volume. Both spectral analysis and cross-correlation of seismic noise showed seasonal reversible variation trends related to air temperature fluctuations. No irreversible changes, resulting from serious damage processes within the rock mass, were detected so far. Modal analysis and geomechanical modeling of the unstable cliff are currently under investigation to better understand the vibration modes that could explain the measured amplitude and orientation of ground motion at the first resonant frequencies. Classification and location of microseismic events still remains the most challenging task, due to the complex structural and morphological setting of the site.

Experimental research on rock fracture failure characteristics under liquid nitrogen cooling conditions

NASA Astrophysics Data System (ADS)

Gao, Feng; Cai, Chengzheng; Yang, Yugui

2018-06-01

As liquid nitrogen is injected into a wellbore as fracturing fluid, it can rapidly absorb heat from warmer rock and generate cryogenic condition in downhole region. This will alter the physical conditions of reservoir rocks and further affect rock failure characteristics. To investigate rock fracture failure characteristics under liquid nitrogen cooling conditions, the fracture features of four types of sandstones and one type of marble were tested on original samples (the sample without any treatment) and cryogenic samples (the samples just taken out from the liquid nitrogen), respectively. The differences between original samples and cryogenic samples in load-displacement curves, fracture toughness, energy evolution and the crack density of ruptured samples were compared and analyzed. The results showed that at elastic deformation stage, cryogenic samples presented less plastic deformation and more obvious brittle failure characteristics than original ones. The average fracture toughness of cryogenic samples was 10.47%-158.33% greater than that of original ones, indicating that the mechanical strength of rocks used were enhanced under cooling conditions. When the samples ruptured, the cryogenic ones were required to absorb more energy and reserve more elastic energy. In general, the fracture degree of cryogenic samples was higher than that of original ones. As the samples were entirely fractured, the crack density of cryogenic samples was about 536.67% at most larger than that of original ones. This indicated that under liquid nitrogen cooling conditions, the stimulation reservoir volume is expected to be improved during fracturing. This work could provide a reference to the research on the mechanical properties and fracture failure of rock during liquid nitrogen fracturing.

Experimental and Computational Studies of Coupled Geomechanical and Hydrologic Processes in Wellbore Systems (Invited)

NASA Astrophysics Data System (ADS)

Carey, J. W.; Mori, H.; Porter, M. L.; Lewis, K. C.; Kelkar, S.

2013-12-01

Potential leakage from wells is an important issue in the protection of groundwater resources, CO2 sequestration, and hydraulic fracturing. The first defense in all of these applications is a properly constructed well with adequate Portland cement that effectively isolates the subsurface. The chief threat for such wells is mechanical disruption of the cement, cement/steel, or cement/caprock interfaces. This can occur through wellbore operations that pressurize/depressurize the steel tubing or create temperature transients (e.g., injection, production, hydraulic fracturing, and mechanical testing) as well as reservoir-scale stresses (e.g., filling or depletion of the reservoir) and tectonic stresses (e.g., the mobility of salt). However, there is relatively limited information available on the hydrologic consequences of such processes. Toward this end, we discuss recent experiments and computational models of coupled geomechanical and hydrologic processes in wellbore systems. Triaxial coreflood experiments with tomography were conducted on synthetic wellbore systems including cement-steel, rock-cement and rock-cement-steel composites. The aim of the experiments was to induce stresses through application of axial loads in order to create defects within the cement or at the cement/steel or cement/rock interface. High injection fluid pressures (supercritical CO2 × brine) were applied to the base of the initially impermeable composites. Mechanical failure resulted in creation of permeability, which was measured as a function of time (allowing for the possibility of Portland cement to deform and modify permeability). In addition, fracture patterns were characterized using x-ray tomography. We used the computer code FEHM to study coupled hydrologic and mechanical processes in the near-wellbore environment. The wellbore model was developed as a wedge within a radially symmetric 3D volume. The grid elements consist of the steel casing, the casing-cement interface, the cement, the cement-rock interface, caprock, and reservoir rock. We used a model that is 1 m in radius, and extends 5 m along the wellbore. The model consisted of a lower storage aquifer, a caprock and an upper aquifer that received leaking fluids. We coupled flow and geomechanics using a shear-failure model that represents shear-induced damage and is similar to a Mohr-Coulomb slip mechanism. In this model, damage occurs for any excess shear stress with permeability enhancement a function of stress with a maximum magnitude set by the user. Stresses were induced by application of an elevated constant pressure within the injection reservoir representing a far-field injection process. The initial permeability of the cement was 1 mD and stress-enhanced permeability was limited to an increase by a factor of 10-100. The simulations show that shear-failure modes lead to enhanced permeability of the wellbore system. Continuing work will examine sensitivity of the results to mechanical properties and initial permeability distributions, the impact of relative permeability models, and the development of permeability-stress models including an aperture-opening tensile-failure model.

Impact of Micro-to Meso-scale Fractures on Sealing Behavior of Argillaceous Cap Rocks For CO 2 Sequestration

DOE Office of Scientific and Technical Information (OSTI.GOV)

Evans, James

This multi-disciplinary project evaluated seal lithologies for the safety and security of long-term geosequestration of CO 2. We used integrated studies to provide qualitative risk for potential seal failure; we integrated data sets from outcrop, core, geochemical analysis, rock failure properties from mechanical testing, geophysical wireline log analysis, and geomechanical modeling to understand the effects of lithologic heterogeneity and changing mechanical properties have on the mechanical properties of the seal. The objectives of this study were to characterize cap rock seals using natural field analogs, available drillhole logging data and whole-rock core, geochemical and isotopic analyses. Rock deformation experiments weremore » carried out on collected samples to develop better models of risk estimation for potential cap rock seal failure. We also sampled variably faulted and fractured cap rocks to examine the impacts of mineralization and/or alteration on the mechanical properties. We compared CO 2 reacted systems to non-CO 2 reacted seal rock types to determine response of each to increased pore fluid pressures and potential for the creation of unintentional hydrofractures at depth.« less

Hydroacoustic monitoring of a salt cavity: an analysis of precursory events of the collapse

NASA Astrophysics Data System (ADS)

Lebert, F.; Bernardie, S.; Mainsant, G.

2011-09-01

One of the main features of "post mining" research relates to available methods for monitoring mine-degradation processes that could directly threaten surface infrastructures. In this respect, GISOS, a French scientific interest group, is investigating techniques for monitoring the eventual collapse of underground cavities. One of the methods under investigation was monitoring the stability of a salt cavity through recording microseismic-precursor signals that may indicate the onset of rock failure. The data were recorded in a salt mine in Lorraine (France) when monitoring the controlled collapse of 2 000 000 m3 of rocks surrounding a cavity at 130 m depth. The monitoring in the 30 Hz to 3 kHz frequency range highlights the occurrence of events with high energy during periods of macroscopic movement, once the layers had ruptured; they appear to be the consequence of the post-rupture rock movements related to the intense deformation of the cavity roof. Moreover the analysis shows the presence of some interesting precursory signals before the cavity collapsed. They occurred a few hours before the failure phases, when the rocks were being weakened and damaged. They originated from the damaging and breaking process, when micro-cracks appear and then coalesce. From these results we expect that deeper signal analysis and statistical analysis on the complete event time distribution (several millions of files) will allow us to finalize a complete typology of each signal families and their relations with the evolution steps of the cavity over the five years monitoring.

Modelling of Dynamic Rock Fracture Process with a Rate-Dependent Combined Continuum Damage-Embedded Discontinuity Model Incorporating Microstructure

NASA Astrophysics Data System (ADS)

Saksala, Timo

2016-10-01

This paper deals with numerical modelling of rock fracture under dynamic loading. For this end, a combined continuum damage-embedded discontinuity model is applied in finite element modelling of crack propagation in rock. In this model, the strong loading rate sensitivity of rock is captured by the rate-dependent continuum scalar damage model that controls the pre-peak nonlinear hardening part of rock behaviour. The post-peak exponential softening part of the rock behaviour is governed by the embedded displacement discontinuity model describing the mode I, mode II and mixed mode fracture of rock. Rock heterogeneity is incorporated in the present approach by random description of the rock mineral texture based on the Voronoi tessellation. The model performance is demonstrated in numerical examples where the uniaxial tension and compression tests on rock are simulated. Finally, the dynamic three-point bending test of a semicircular disc is simulated in order to show that the model correctly predicts the strain rate-dependent tensile strengths as well as the failure modes of rock in this test. Special emphasis is laid on modelling the loading rate sensitivity of tensile strength of Laurentian granite.

Coupled THM processes in EDZ of crystalline rocks using an elasto-plastic cellular automaton

NASA Astrophysics Data System (ADS)

Pan, Peng-Zhi; Feng, Xia-Ting; Huang, Xiao-Hua; Cui, Qiang; Zhou, Hui

2009-05-01

This paper aims at a numerical study of coupled thermal, hydrological and mechanical processes in the excavation disturbed zones (EDZ) around nuclear waste emplacement drifts in fractured crystalline rocks. The study was conducted for two model domains close to an emplacement tunnel; (1) a near-field domain and (2) a smaller wall-block domain. Goodman element and weak element were used to represent the fractures in the rock mass and the rock matrix was represented as elasto-visco-plastic material. Mohr-Coulomb criterion and a non-associated plastic flow rule were adopted to consider the viscoplastic deformation in the EDZ. A relation between volumetric strain and permeability was established. Using a self-developed EPCA2D code, the elastic, elasto-plastic and creep analyses to study the evolution of stress and deformations, as well as failure and permeability evolution in the EDZ were conducted. Results indicate a strong impact of fractures, plastic deformation and time effects on the behavior of EDZ especially the evolution of permeability around the drift.

Numerical built-in method for the nonlinear JRC/JCS model in rock joint.

PubMed

Liu, Qunyi; Xing, Wanli; Li, Ying

2014-01-01

The joint surface is widely distributed in the rock, thus leading to the nonlinear characteristics of rock mass strength and limiting the effectiveness of the linear model in reflecting characteristics. The JRC/JCS model is the nonlinear failure criterion and generally believed to describe the characteristics of joints better than other models. In order to develop the numerical program for JRC/JCS model, this paper established the relationship between the parameters of the JRC/JCS and Mohr-Coulomb models. Thereafter, the numerical implement method and implementation process of the JRC/JCS model were discussed and the reliability of the numerical method was verified by the shear tests of jointed rock mass. Finally, the effect of the JRC/JCS model parameters on the shear strength of the joint was analyzed.

Evaluation of TBM tunnels with respect to stability against spalling

NASA Astrophysics Data System (ADS)

Shaalan, Heyam; Ismail, Mohd Ashraf Mohd; Azit, Romziah

2017-10-01

As the depth of tunnels and underground construction increases, instability occurs in the form of rock bursting or spalling because of the induced stresses. Spalling may appear as a strong compressive stress causing crack growth behind the excavated surface and buckling of the thin rock slabs. In this paper, we describe how to reduce the rock spalling failure to increase the underground safety and the tunnel stability. Thus, a parametric study is implemented using 2-D Elasto-plastic finite elements stress analysis software to investigate the parameters that can minimize the extent and depth of the failure zone. The critical section of Pahang Selangor Raw Water Transfer Tunnel under high overburden is analyzed. The effect of the shotcrete lining thickness, tunnel size and the removal of fallouts or scaled v-notch on the failure zone depth is investigated. The results demonstrate that the shotcrete lining thickness has less influence on the failure depth, while a small tunnel diameter minimizes the failure depth. In addition, the stability of the tunnel improves by removing the loose rock mass.

Analytical Solution of Displacements Around Circular Openings in Generalized Hoek-Brown Rocks

NASA Astrophysics Data System (ADS)

Huang, Houxu; Li, Jie; Wei, Jiuqi

2017-09-01

The rock in plastic region is divided into numbers of elements by the slip lines, resulted from shear localization. During the deformation process, the elements will slip along the slip lines and the displacement field is discontinuous. Slip lines around circular opening in isotropic rock, subjected to hydrostatic stress are described by the logarithmic spirals. Deformation of the plastic region is mainly attributed to the slippage. Relationship between the shear stresses and slippage on slip lines is presented, based on the study of Revuzhenko and Shemyakin. Relations between slippage and rock failure are described, based on the elastic-brittle-plastic model. An analytical solution is presented for the plane strain analysis of displacements around circular openings in the Generalized Hoek-Brown rock. With properly choosing of slippage parameters, results obtained by using the proposed solution agree well with those presented in published sources.

A New Rock Strength Criterion from Microcracking Mechanisms Which Provides Theoretical Evidence of Hybrid Failure

NASA Astrophysics Data System (ADS)

Zhu, Qi-Zhi

2017-02-01

A proper criterion describing when material fails is essential for deep understanding and constitutive modeling of rock damage and failure by microcracking. Physically, such a criterion should be the global effect of local mechanical response and microstructure evolution inside the material. This paper aims at deriving a new mechanisms-based failure criterion for brittle rocks, based on micromechanical unilateral damage-friction coupling analyses rather than on the basic results from the classical linear elastic fracture mechanics. The failure functions respectively describing three failure modes (purely tensile mode, tensile-shear mode as well as compressive-shear mode) are achieved in a unified upscaling framework and illustrated in the Mohr plane and also in the plane of principal stresses. The strength envelope is proved to be continuous and smooth with a compressive to tensile strength ratio dependent on material properties. Comparisons with experimental data are finally carried out. By this work, we also provide a theoretical evidence on the hybrid failure and the smooth transition from tensile failure to compressive-shear failure.

Simulating Hydraulic Fracturing: Failure in soft versus hard rocks

NASA Astrophysics Data System (ADS)

Aleksans, J.; Koehn, D.; Toussaint, R.

2017-12-01

In this contribution we discuss the dynamic development of hydraulic fractures, their evolution and the resulting seismicity during fluid injection in a coupled numerical model. The model describes coupling between a solid that can fracture dynamically and a compressible fluid that can push back at the rock and open fractures. With a series of numerical simulations we show how the fracture pattern and seismicity change depending on changes in depth, injection rate, Young's Modulus and breaking strength. Our simulations indicate that the Young's Modulus has the largest influence on the fracture dynamics and also the related seismicity. Simulations of rocks with a Young's modulus smaller than 10 GPa show dominant mode I failure and a growth of fracture aperture with a decrease in Young's modulus. Simulations of rocks with a higher Young's modulus than 10 GPa show fractures with a constant aperture and fracture growth that is mainly governed by a growth in crack length and an increasing amount of mode II failure. We propose that two distinct failure regimes are observed in the simulations, above 10 GPa rocks break with a constant critical stress intensity factor whereas below 10 GPa they break reaching a critical cohesion, i.e. a critical tensile strength. These results are very important for the prediction of fracture dynamics and seismicity during fluid injection, especially since we see a transition from one failure regime to another at around 10 GPa, a Young's modulus that lies in the middle of possible values for natural shale rocks.

Joint-bounded crescentic scars formed by subglacial clast-bed contact forces: Implications for bedrock failure beneath glaciers

NASA Astrophysics Data System (ADS)

Krabbendam, M.; Bradwell, T.; Everest, J. D.; Eyles, N.

2017-08-01

Glaciers and ice sheets are important agents of bedrock erosion, yet the precise processes of bedrock failure beneath glacier ice are incompletely known. Subglacially formed erosional crescentic markings (crescentic gouges, lunate fractures) on bedrock surfaces occur locally in glaciated areas and comprise a conchoidal fracture dipping down-ice and a steep fracture that faces up-ice. Here we report morphologically distinct crescentic scars that are closely associated with preexisting joints, termed here joint-bounded crescentic scars. These hitherto unreported features are ca. 50-200 mm deep and involve considerably more rock removal than previously described crescentic markings. The joint-bounded crescentic scars were found on abraded rhyolite surfaces recently exposed (< 20 years) beneath a retreating glacier in Iceland, as well as on glacially sculpted Precambrian gneisses in NW Scotland and various Precambrian rocks in Ontario, glaciated during the Late Pleistocene. We suggest a common formation mechanism for these contemporary and relict features, whereby a boulder embedded in basal ice produces a continuously migrating clast-bed contact force as it is dragged over the hard (bedrock) bed. As the ice-embedded boulder approaches a preexisting joint in the bedrock, stress concentrations build up in the bed that exceed the intact rock strength, resulting in conchoidal fracturing and detachment of a crescentic wedge-shaped rock fragment. Subsequent removal of the rock fragment probably involves further fracturing or crushing (comminution) under high contact forces. Formation of joint-bounded crescentic scars is favoured by large boulders at the base of the ice, high basal melting rates, and the presence of preexisting subvertical joints in the bedrock bed. We infer that the relative scarcity of crescentic markings in general on deglaciated surfaces shows that fracturing of intact bedrock below ice is difficult, but that preexisting weaknesses such as joints greatly facilitate rock failure. This implies that models of glacial erosion need to take fracture patterns of bedrock into account.

Modeling Micro-cracking Behavior of Bukit Timah Granite Using Grain-Based Model

NASA Astrophysics Data System (ADS)

Peng, Jun; Wong, Louis Ngai Yuen; Teh, Cee Ing; Li, Zhihuan

2018-01-01

Rock strength and deformation behavior has long been recognized to be closely related to the microstructure and the associated micro-cracking process. A good understanding of crack initiation and coalescence mechanisms will thus allow us to account for the variation of rock strength and deformation properties from a microscopic view. This paper numerically investigates the micro-cracking behavior of Bukit Timah granite by using a grain-based modeling approach. First, the principles of grain-based model adopted in the two-dimensional Particle Flow Code and the numerical model generation procedure are reviewed. The micro-parameters of the numerical model are then calibrated to match the macro-properties of the rock obtained from tension and compression tests in the laboratory. The simulated rock properties are in good agreement with the laboratory test results with the errors less than ±6%. Finally, the calibrated model is used to study the micro-cracking behavior and the failure modes of the rock under direct tension and under compression with different confining pressures. The results reveal that when the numerical model is loaded in direct tension, only grain boundary tensile cracks are generated, and the simulated macroscopic fracture agrees well with the results obtained in laboratory tests. When the model is loaded in compression, the ratio of grain boundary tensile cracks to grain boundary shear cracks decreases with the increase in confining pressure. In other words, the results show that as the confining pressure increases, the failure mechanism changes from tension to shear. The simulated failure mode of the model changes from splitting to shear as the applied confining pressure gradually increases, which is comparable with that observed in laboratory tests. The grain-based model used in this study thus appears promising for further investigation of microscopic and macroscopic behavior of crystalline rocks under different loading conditions.

TOUGH2Biot - A simulator for coupled thermal-hydrodynamic-mechanical processes in subsurface flow systems: Application to CO2 geological storage and geothermal development

NASA Astrophysics Data System (ADS)

Lei, Hongwu; Xu, Tianfu; Jin, Guangrong

2015-04-01

Coupled thermal-hydrodynamic-mechanical processes have become increasingly important in studying the issues affecting subsurface flow systems, such as CO2 sequestration in deep saline aquifers and geothermal development. In this study, a mechanical module based on the extended Biot consolidation model was developed and incorporated into the well-established thermal-hydrodynamic simulator TOUGH2, resulting in an integrated numerical THM simulation program TOUGH2Biot. A finite element method was employed to discretize space for rock mechanical calculation and the Mohr-Coulomb failure criterion was used to determine if the rock undergoes shear-slip failure. Mechanics is partly coupled with the thermal-hydrodynamic processes and gives feedback to flow through stress-dependent porosity and permeability. TOUGH2Biot was verified against analytical solutions for the 1D Terzaghi consolidation and cooling-induced subsidence. TOUGH2Biot was applied to evaluate the thermal, hydrodynamic, and mechanical responses of CO2 geological sequestration at the Ordos CCS Demonstration Project, China and geothermal exploitation at the Geysers geothermal field, California. The results demonstrate that TOUGH2Biot is capable of analyzing change in pressure and temperature, displacement, stress, and potential shear-slip failure caused by large scale underground man-made activity in subsurface flow systems. TOUGH2Biot can also be easily extended for complex coupled process problems in fractured media and be conveniently updated to parallel versions on different platforms to take advantage of high-performance computing.

Numerical model of thermo-mechanical coupling for the tensile failure process of brittle materials

NASA Astrophysics Data System (ADS)

Fu, Yu; Wang, Zhe; Ren, Fengyu; Wang, Daguo

2017-10-01

A numerical model of thermal cracking with a thermo-mechanical coupling effect was established. The theory of tensile failure and heat conduction is used to study the tensile failure process of brittle materials, such as rock and concrete under high temperature environment. The validity of the model is verified by thick-wall cylinders with analytical solutions. The failure modes of brittle materials under thermal stresses caused by temperature gradient and different thermal expansion coefficient were studied by using a thick-wall cylinder model and an embedded particle model, respectively. In the thick-wall cylinder model, different forms of cracks induced by temperature gradient were obtained under different temperature boundary conditions. In the embedded particle model, radial cracks were produced in the medium part with lower tensile strength when temperature increased because of the different thermal expansion coefficient. Model results are in good agreement with the experimental results, thereby providing a new finite element method for analyzing the thermal damage process and mechanism of brittle materials.

Interesting insights into instability of slopes and rock fall in the morphodynamic Himalayan terrane

NASA Astrophysics Data System (ADS)

Singh, T. N.; Vishal, V.; Pradhan, S. P.

2015-12-01

Himalayan mountain ranges are tectonically and seismically very active and experience many disastrous events with time due to slope failure. Frequent failures of rock cut slopes cause obstruction in traffic and often lead to fatalities. In recent years, the number of tragedies has increased when associated with regional phenomena such at the Kedarnath tragedy of 2013 and the Gorkha earthquake of 2015. The influence of such phenomena on the stability of slopes along important national highways and key settlement areas only raise the risk to lives and property. We conducted a multi-approach investigation for some key slopes along the National Highway 58 in Uttarakhand Himalaya, India. A very detailed field work was conducted to identify the unstable slopes and those with some history of failure. The pertinent geomechanical characteristics of the representative rock samples were determined in the laboratory. Based on the structural data, kinematic analysis was carried out. Finally the slopes were simulated using FDM based simulator, Flac/Slope for analysing the health of the slopes and Rockfall 4.0 to investigate the phenomenon of rockfall along the Highway. It was found that few slopes were weak due to the inherent weak rock materials while few slopes made up of high strength rocks were effectively weak due to prone-to-failure orientation of the joints. Quantification of bounce-height of rock blocks during fall, their energy, velocity and displacement along the slope was also done. Using 3-D simulations, few critically-stable slopes that appear to be stable, were identified. Little ground movement could be capable of triggering a large scale failure in the area. Slopes in the studied region are under threat to failure and need immediate proper planning using the suggested remedial measures.

Collaborative Research: failure of RockMasses from Nucleation and Growth of Microscopic Defects and Disorder

DOE Office of Scientific and Technical Information (OSTI.GOV)

Klein, William

Over the 21 years of funding we have pursued several projects related to earthquakes, damage and nucleation. We developed simple models of earthquake faults which we studied to understand Gutenburg-Richter scaling, foreshocks and aftershocks, the effect of spatial structure of the faults and its interaction with underlying self organization and phase transitions. In addition we studied the formation of amorphous solids via the glass transition. We have also studied nucleation with a particular concentration on transitions in systems with a spatial symmetry change. In addition we investigated the nucleation process in models that mimic rock masses. We obtained the structuremore » of the droplet in both homogeneous and heterogeneous nucleation. We also investigated the effect of defects or asperities on the nucleation of failure in simple models of earthquake faults.« less

Crack propagation of brittle rock under high geostress

NASA Astrophysics Data System (ADS)

Liu, Ning; Chu, Weijiang; Chen, Pingzhi

2018-03-01

Based on fracture mechanics and numerical methods, the characteristics and failure criterions of wall rock cracks including initiation, propagation, and coalescence are analyzed systematically under different conditions. In order to consider the interaction among cracks, adopt the sliding model of multi-cracks to simulate the splitting failure of rock in axial compress. The reinforcement of bolts and shotcrete supporting to rock mass can control the cracks propagation well. Adopt both theory analysis and simulation method to study the mechanism of controlling the propagation. The best fixed angle of bolts is calculated. Then use ansys to simulate the crack arrest function of bolt to crack. Analyze the influence of different factors on stress intensity factor. The method offer more scientific and rational criterion to evaluate the splitting failure of underground engineering under high geostress.

Understanding tectonic stress and rock strength in the Nankai Trough accretionary prism, offshore SW Japan

NASA Astrophysics Data System (ADS)

Huffman, Katelyn A.

Understanding the orientation and magnitude of tectonic stress in active tectonic margins like subduction zones is important for understanding fault mechanics. In the Nankai Trough subduction zone, faults in the accretionary prism are thought to have historically slipped during or immediately following deep plate boundary earthquakes, often generating devastating tsunamis. I focus on quantifying stress at two locations of interest in the Nankai Trough accretionary prism, offshore Southwest Japan. I employ a method to constrain stress magnitude that combines observations of compressional borehole failure from logging-while-drilling resistivity-at-the-bit generated images (RAB) with estimates of rock strength and the relationship between tectonic stress and stress at the wall of a borehole. I use the method to constrain stress at Ocean Drilling Program (ODP) Site 808 and Integrated Ocean Drilling Program (IODP) Site C0002. At Site 808, I consider a range of parameters (assumed rock strength, friction coefficient, breakout width, and fluid pressure) in the method to constrain stress to explore uncertainty in stress magnitudes and discuss stress results in terms of the seismic cycle. I find a combination of increased fluid pressure and decreased friction along the frontal thrust or other weak faults could produce thrust-style failure, without the entire prism being at critical state failure, as other kinematic models of accretionary prism behavior during earthquakes imply. Rock strength is typically inferred using a failure criterion and unconfined compressive strength from empirical relations with P-wave velocity. I minimize uncertainty in rock strength by measuring rock strength in triaxial tests on Nankai core. I find strength of Nankai core is significantly less than empirical relations predict. I create a new empirical fit to our experiments and explore implications of this on stress magnitude estimates. I find using the new empirical fit can decrease stress predicted in the method by as much as 4 MPa at Site C0002. I constrain stress at Site C0002 using geophysical logging data from two adjacent boreholes drilled into the same sedimentary sequence with different drilling conditions in a forward model that predicts breakout width over a range of horizontal stresses (where SHmax is constrained by the ratio of stresses that would produce active faulting and Shmin is constrained from leak-off-tests) and rock strength. I then compare predicted breakout widths to observations of breakout widths from RAB images to determine the combination of stresses in the model that best match real world observations. This is the first published method to constrain both stress and strength simultaneously. Finally, I explore uncertainty in rock behavior during compressional breakout formation using a finite element model (FEM) that predicts Biot poroelastic changes in fluid pressure in rock adjacent to the borehole upon its excavation and explore the effect this has on rock failure. I test a range of permeability and rock stiffness. I find that when rock stiffness and permeability are in the range of what exists at Nankai, pore fluid pressure increase +/- 45° from Shmin and can lead to weakening of wall rock and a wider compressional failure zone than what would exist at equilibrium conditions. In a case example at, we find this can lead to an overestimate of tectonic stress using compressional failures of ~2 MPa in the area of the borehole where fluid pressure increases. In areas around the borehole where pore fluid decreases (+/- 45° from SHmax), the wall rock can strengthen which suppresses tensile failure. The implications of this research is that there are many potential pitfalls in the method to constrain stress using borehole breakouts in Nankai Trough mudstone, mostly due to uncertainty in parameters such as strength and underlying assumptions regarding constitutive rock behavior. More laboratory measurement and/or models of rock properties and rock constitutive behavior is needed to ensure the method is accurately providing constraints on stress magnitude. (Abstract shortened by ProQuest.).

Brittle failure of rock: A review and general linear criterion

NASA Astrophysics Data System (ADS)

Labuz, Joseph F.; Zeng, Feitao; Makhnenko, Roman; Li, Yuan

2018-07-01

A failure criterion typically is phenomenological since few models exist to theoretically derive the mathematical function. Indeed, a successful failure criterion is a generalization of experimental data obtained from strength tests on specimens subjected to known stress states. For isotropic rock that exhibits a pressure dependence on strength, a popular failure criterion is a linear equation in major and minor principal stresses, independent of the intermediate principal stress. A general linear failure criterion called Paul-Mohr-Coulomb (PMC) contains all three principal stresses with three material constants: friction angles for axisymmetric compression ϕc and extension ϕe and isotropic tensile strength V0. PMC provides a framework to describe a nonlinear failure surface by a set of planes "hugging" the curved surface. Brittle failure of rock is reviewed and multiaxial test methods are summarized. Equations are presented to implement PMC for fitting strength data and determining the three material parameters. A piecewise linear approximation to a nonlinear failure surface is illustrated by fitting two planes with six material parameters to form either a 6- to 12-sided pyramid or a 6- to 12- to 6-sided pyramid. The particular nature of the failure surface is dictated by the experimental data.

Dynamic Brazilian Test of Rock Under Intermediate Strain Rate: Pendulum Hammer-Driven SHPB Test and Numerical Simulation

NASA Astrophysics Data System (ADS)

Zhu, W. C.; Niu, L. L.; Li, S. H.; Xu, Z. H.

2015-09-01

The tensile strength of rock subjected to dynamic loading constitutes many engineering applications such as rock drilling and blasting. The dynamic Brazilian test of rock specimens was conducted with the split Hopkinson pressure bar (SHPB) driven by pendulum hammer, in order to determine the indirect tensile strength of rock under an intermediate strain rate ranging from 5.2 to 12.9 s-1, which is achieved when the incident bar is impacted by pendulum hammer with different velocities. The incident wave excited by pendulum hammer is triangular in shape, featuring a long rising time, and it is considered to be helpful for achieving a constant strain rate in the rock specimen. The dynamic indirect tensile strength of rock increases with strain rate. Then, the numerical simulator RFPA-Dynamics, a well-recognized software for simulating the rock failure under dynamic loading, is validated by reproducing the Brazilian test of rock when the incident stress wave retrieved at the incident bar is input as the boundary condition, and then it is employed to study the Brazilian test of rock under the higher strain rate. Based on the numerical simulation, the strain-rate dependency of tensile strength and failure pattern of the Brazilian disc specimen under the intermediate strain rate are numerically simulated, and the associated failure mechanism is clarified. It is deemed that the material heterogeneity should be a reason for the strain-rate dependency of rock.

Age evaluation and causation of rock-slope failures along the western margin of the Antrim Lava Group (ALG), Northern Ireland, based on cosmogenic isotope (36Cl) surface exposure dating

NASA Astrophysics Data System (ADS)

Southall, David W.; Wilson, Peter; Dunlop, Paul; Schnabel, Christoph; Rodés, Ángel; Gulliver, Pauline; Xu, Sheng

2017-05-01

The temporal pattern of postglacial rock-slope failure in a glaciated upland area of Ireland (the western margin of the Antrim Lava Group) was evaluated using both 36Cl exposure dating of surface boulders on run-out debris and 14C dating of basal organic soils from depressions on the debris. The majority of the 36Cl ages ( 21-15 ka) indicate that major failures occurred during or immediately following local deglaciation ( 18-17 ka). Other ages ( 14-9 ka) suggest some later, smaller-scale failures during the Lateglacial and/or early Holocene. The 14C ages (2.36-0.15 cal ka BP) indicate the very late onset of organic accumulation and do not provide close limiting age constraints. Rock-slope failure during or immediately following local deglaciation was probably in response to some combination of glacial debuttressing, slope steepening and paraglacial stress release. Later failures may have been triggered by seismic activity associated with glacio-isostatic crustal uplift and/or permafrost degradation consequent upon climate change. The 36Cl ages support the findings of previous studies that show the deglacial - Lateglacial period in northwest Ireland and Scotland to have been one of enhanced rock-slope failure. Table S2 Concentrations of main elements (as oxides) etc.

Rupture directivity of microseismic events recorded during hydraulic fracture stimulations.

NASA Astrophysics Data System (ADS)

Urbancic, T.; Smith-Boughner, L.; Baig, A.; Viegas, G.

2016-12-01

We model the dynamics of a complex rupture sequence with four sub-events. These events were recorded during hydraulic fracture stimulations in a gas-bearing shale formation. With force-balance accelerometers, 4.5Hz and 15Hz instruments recording the failure history, we study the directivity of the entire rupture sequence and each sub-event. Two models are considered: unilateral and bi-lateral failures of penny shaped cracks. From the seismic moment tensors of these sub-events, we consider different potential failure planes and rupture directions. Using numerical wave-propagation codes, we generate synthetic rupture sequences with both unilateral and bi-lateral ruptures. These are compared to the four sub-events to determine the directionality of the observed failures and the sensitivity of our recording bandwidth and geometry to distinguishing between different rupture processes. The frequency of unilateral and bilateral rupture processes throughout the fracture stimulation is estimated by comparing the directivity characteristics of the modeled sub-events to other high-quality microseismic events recorded during the same stimulation program. Understanding the failure processes of these microseismic events can provide great insight into the changes in the rock mass responsible for these complex rupture processes.

Effect law of Damage Characteristics of Rock Similar Material with Pre-Existing Cracks

NASA Astrophysics Data System (ADS)

Li, S. G.; Cheng, X. Y.; Liu, C.

2017-11-01

In order to further study the failure mechanism for rock similar materials, this study established the damage model based on accumulative AE events, investigated the damage characteristics for rock similar material samples with pre-existing cracks of varying width under uniaxial compression load. The equipment used in this study is the self-developed YYW-II strain controlled unconfined compression apparatus and the PCIE-8 acoustic emission (AE) monitoring system. The influences of the width of the pre-existing cracks to the damage characteristics of rock similar materials are analyzed. Results show that, (1) the damage model can better describe the damage characteristics of rock similar materials; (2) the tested samples have three stages during failure: initial damage stage, stable development of damage stage, and accelerated development of damage stage; (3) with the width of pre-existing cracks vary from 3mm to 5mm, the damage of rock similar materials increases gradually. The outcomes of this study provided additional values to the research of the failure mechanism for geotechnical similar material models.

Inexpensive Device for Demonstrating Rock Slope Failure and Other Collapse Phenomena.

ERIC Educational Resources Information Center

Stimpson, B.

1980-01-01

Describes an inexpensive modeling technique for demonstrating large-scale displacement phenomena in rock masses, such as slope collapse and failure of underground openings. Excavation of the model material occurs through openings made in the polyurethane foam in the correct excavation sequence. (Author/SA)

Predicting rock bursts in mines

USGS Publications Warehouse

Spall, H.

1979-01-01

The microseismic method relies on observational data, amply demonstrated in laboratory experiments, that acoustic noise occurs in rocks subjected to high differential stresses. Acoustic emission becomes most pronounced as the breaking strength of the rock is reached. Laboratory studies have shown that the acoustic emission is linked with the release of stored strain energy as the rock mass undergoes small-scale adjustments such as the formation of cracks. Studies in actual mines have shown that acoustic noises often precede failure of rock masses in rock bursts or in coal bumps. Seismologists are, therefore, very interested in whether these results can be applied to large-scale failures; that is, earthquakes. An active research program in predicting rock bursts in mines is being conducted by Brian T. Brady and his colleagues at the U.S Bureau of Mines, Denver Colo.  

Sill intrusion in volcanic calderas: implications for vent opening probability

NASA Astrophysics Data System (ADS)

Giudicepietro, Flora; Macedonio, Giovanni; Martini, Marcello; D'Auria, Luca

2017-04-01

Calderas show peculiar behaviors with remarkable dynamic processes, which do not often culminate in eruptions. Observations and studies conducted in recent decades have shown that the most common cause of unrest in the calderas is due to magma intrusion; in particular, the intrusion of sills at shallow depths. Monogenic cones, with large areal dispersion, are quite common in the calderas, suggesting that the susceptibility analysis based on geological features, is not strictly suitable for estimating the vent opening probability in calderas. In general, the opening of a new eruptive vent can be regarded as a rock failure process. The stress field in the rocks that surrounds and tops the magmatic reservoirs plays an important role in causing the rock failure and creating the path that magma can follow towards the surface. In this conceptual framework, we approach the problem of getting clues about the probability of vent opening in volcanic calderas through the study of the stress field produced by the intrusion of magma, in particular, by the intrusion of a sill. We simulate the intrusion of a sill free to expand radially, with shape and dimensions which vary with time. The intrusion process is controlled by the elastic response of the rock plate above the sill, which bends because of the intrusion, and by gravity, that drives the magma towards the zones where the thickness of the sill is smaller. We calculated the stress field in the plate rock above the sill. We found that at the bottom of the rock plate above the sill the maximum intensity of tensile stress is concentrated at the front of the sill and spreads radially with it, over time. For this reason, we think that the front of the spreading sill is prone to open for eruptive vents. Even in the central area of the sill the intensity of stress is relatively high, but at the base of the rock plate stress is compressive. Under isothermal conditions, the stress soon reaches its maximum value (time interval depending on the model parameters) and then decreases over time during the intrusion. However, if we consider the effect of the cooling of magma, with the temperature which decreases with time and the viscosity that increases, we'll find that the stress in the rock above the sill gradually increases with time and becomes higher than in isothermal case. In order to investigate the role of the physical properties of magma and rock above the sill in the generation of the stress field we have carried out different simulations by varying the viscosity of magma and the rigidity of the rock and found that high viscosity magma produces a relatively high stress intensity, as well as a high rock rigidity does.

Influence of Weathering Depth and Fracture Intensity to Cut-slope Movements

NASA Astrophysics Data System (ADS)

Yoon, W. S.; Choi, J. W.; Jeong, U.; Kim, J. H.

2003-04-01

Generally, Failure modes in cut slopes are triggered by combination of various failure factors which have different effects on failure modes according to ground condition. It is, therefore, important to identify the behavioural characteristic of cut slope in that they reflect the failure mechanism. From the careful field investigation for 373 road cuts along the national highway in Korea, we analysed various types of failure modes for different ground conditions. The ground conditions which control failure modes of cut slopes and their related failure factors are dependent on weathering (or soil) depth and intensity of discontinuities in cut slopes. Firstly, the ratio of the soil depth and slope height (soil depth ratio; SR) is important parameter to classify ground conditions into soil-like masses and rock masses. When a SR value is greater than 0.4, sliding failures on discontinuities do not occur. In this case, weathering condition, slope gradient and external rainfall play a key role on failure factors of cut-slope. The proposed 0.4, therefore, is the critical SR value to identify the soil-like masses and rock masses. Secondly, Intensity of discontinuities is expressed by block size ratio (BR), which is defined by the ratio of block size index (Ib; ISRM (1978)) and slope height. For a rock slope (SR<0.4), when BR is greater than 0.01, key failure modes in a cut slope are wedge sliding, fall and topple. In this case, attitudes and shear strength of discontinuities play an important role on behaviour of cut-slope. When BR is less than 0.01, however, behaviour of cut slope shows circular sliding and surface failure like soil-like mass. To sum up, we could divide the ground conditions in cut-slope into 3 classes on the basis of SR (soil depth ratio) and BR (block size ratio); JRM (joint rock mass), HRM (highly fractured rock mass) and SLM (soil-like mass). Moreover, to evaluate the stability of cut-slope reasonably, it needs new evaluating categories having different weighting factors for each ground condition.

Landslides and dam damage resulting from the Jiuzhaigou earthquake (8 August 2017), Sichuan, China

PubMed Central

Wang, Yun-sheng; Luo, Yong-hong; Li, Jia; Zhang, Xin; Shen, Tong

2018-01-01

At 21.19 on 8 August 2017, an Ms 7.0 earthquake struck the Jiuzhaigou scenic spot in northwestern Sichuan Province, China. The Jiuzhaigou earthquake is a strike-slip earthquake with a focal depth of 20 km at 33.20° N and 103.82° E, and was caused by two concealed faults. According to emergency investigations and remote sensing interpretations, the Jiuzhaigou earthquake triggered 1780 landslides, damaged one dam (Nuorilang Waterfall) and broke one dam (Huohua Lake). The landslides mainly occurred in the Rize Valley and Shuzheng Valley and in Jiuzhai Paradise. The landslides involved hanging wall and back-slope effects, and the slope angle, slope aspect, seismic faults and valley trend were obviously related to the occurrence of the landslides. Specifically, most of the landslides were shallow landslides, rockfalls and rock avalanches and were small in scale. The failure modes of landslides mainly include wedge rock mass failure, residual deposit failure, relaxed rock mass failure and weathered rock mass failure. The initial low stability of the dam coupled with the topographic effect, back-slope effect and excess pore water pressure led to damage to the Nuorilang Waterfall dam. PMID:29657755

Landslides and dam damage resulting from the Jiuzhaigou earthquake (8 August 2017), Sichuan, China

NASA Astrophysics Data System (ADS)

Zhao, Bo; Wang, Yun-sheng; Luo, Yong-hong; Li, Jia; Zhang, Xin; Shen, Tong

2018-03-01

At 21.19 on 8 August 2017, an Ms 7.0 earthquake struck the Jiuzhaigou scenic spot in northwestern Sichuan Province, China. The Jiuzhaigou earthquake is a strike-slip earthquake with a focal depth of 20 km at 33.20° N and 103.82° E, and was caused by two concealed faults. According to emergency investigations and remote sensing interpretations, the Jiuzhaigou earthquake triggered 1780 landslides, damaged one dam (Nuorilang Waterfall) and broke one dam (Huohua Lake). The landslides mainly occurred in the Rize Valley and Shuzheng Valley and in Jiuzhai Paradise. The landslides involved hanging wall and back-slope effects, and the slope angle, slope aspect, seismic faults and valley trend were obviously related to the occurrence of the landslides. Specifically, most of the landslides were shallow landslides, rockfalls and rock avalanches and were small in scale. The failure modes of landslides mainly include wedge rock mass failure, residual deposit failure, relaxed rock mass failure and weathered rock mass failure. The initial low stability of the dam coupled with the topographic effect, back-slope effect and excess pore water pressure led to damage to the Nuorilang Waterfall dam.

Landslides and dam damage resulting from the Jiuzhaigou earthquake (8 August 2017), Sichuan, China.

PubMed

Zhao, Bo; Wang, Yun-Sheng; Luo, Yong-Hong; Li, Jia; Zhang, Xin; Shen, Tong

2018-03-01

At 21.19 on 8 August 2017, an Ms 7.0 earthquake struck the Jiuzhaigou scenic spot in northwestern Sichuan Province, China. The Jiuzhaigou earthquake is a strike-slip earthquake with a focal depth of 20 km at 33.20° N and 103.82° E, and was caused by two concealed faults. According to emergency investigations and remote sensing interpretations, the Jiuzhaigou earthquake triggered 1780 landslides, damaged one dam (Nuorilang Waterfall) and broke one dam (Huohua Lake). The landslides mainly occurred in the Rize Valley and Shuzheng Valley and in Jiuzhai Paradise. The landslides involved hanging wall and back-slope effects, and the slope angle, slope aspect, seismic faults and valley trend were obviously related to the occurrence of the landslides. Specifically, most of the landslides were shallow landslides, rockfalls and rock avalanches and were small in scale. The failure modes of landslides mainly include wedge rock mass failure, residual deposit failure, relaxed rock mass failure and weathered rock mass failure. The initial low stability of the dam coupled with the topographic effect, back-slope effect and excess pore water pressure led to damage to the Nuorilang Waterfall dam.

An experimental method to quantify the impact fatigue behavior of rocks

NASA Astrophysics Data System (ADS)

Wu, Bangbiao; Kanopoulos, Patrick; Luo, Xuedong; Xia, Kaiwen

2014-07-01

Fatigue failure is an important failure mode of engineering materials. The fatigue behavior of both ductile and brittle materials has been under investigation for many years. While the fatigue failure of ductile materials is well established, only a few studies have been carried out on brittle materials. In addition, most fatigue studies on rocks are conducted under quasi-static loading conditions. To address engineering applications involving repeated blasting, this paper proposes a method to quantify the impact fatigue properties of rocks. In this method, a split Hopkinson pressure bar system is adopted to exert impact load on the sample, which is placed in a specially designed steel sleeve to limit the displacement of the sample and thus to enable the recovery of the rock after each impact. The method is then applied to Laurentian granite, which is fine-grained and isotropic material. The results demonstrate that this is a practicable means to conduct impact fatigue tests on rocks and other brittle solids.

Volcano collapse promoted by progressive strength reduction: New data from Mount St. Helens

USGS Publications Warehouse

Reid, Mark E.; Keith, Terry E.C.; Kayen, Robert E.; Iverson, Neal R.; Iverson, Richard M.; Brien, Dianne

2010-01-01

Rock shear strength plays a fundamental role in volcano flank collapse, yet pertinent data from modern collapse surfaces are rare. Using samples collected from the inferred failure surface of the massive 1980 collapse of Mount St. Helens (MSH), we determined rock shear strength via laboratory tests designed to mimic conditions in the pre-collapse edifice. We observed that the 1980 failure shear surfaces formed primarily in pervasively shattered older dome rocks; failure was not localized in sloping volcanic strata or in weak, hydrothermally altered rocks. Our test results show that rock shear strength under large confining stresses is reduced ∼20% as a result of large quasi-static shear strain, as preceded the 1980 collapse of MSH. Using quasi-3D slope-stability modeling, we demonstrate that this mechanical weakening could have provoked edifice collapse, even in the absence of transiently elevated pore-fluid pressures or earthquake ground shaking. Progressive strength reduction could promote collapses at other volcanic edifices.

Water saturation of hydrothermal smectite-rich clay might have promoted slope instability prior to the 1998 debris avalanche at Casita volcano, Nicaragua

NASA Astrophysics Data System (ADS)

Delmelle, P.; Opfergelt, S.; Boivin, P.; Delvaux, B.

2006-12-01

In October 1998, a relatively small collapse (1 600 000 cubic meters) of a pre-existing scarp occurred on the southern flank of the dormant Casita volcano, Nicaragua. It resulted in a debris avalanche, which quickly transformed into a disastrous debris flow that destroyed two towns and killed more than 2500 people. The failure was shown to be triggered by an excess pore water pressure within highly fractured rocks, following prolonged seasonal rains and precipitations from Hurricane Mitch. This pressure was linked to the water saturation of a hydrothermally-altered clay bedrock impeding in-depth infiltration. Yet, the nature and amounts of the clay material involved in the slope failure were still unknown. Here we report on physical, chemical and mineralogical investigations aimed at quantifying the clay content, and identifying the layer silicates of the hydrothermally-altered clays uncovered by the 1998 debris avalanche. The fine clay material was exceptionally rich in smectite (up to 50 wt. percent), which swells upon wetting and shrinks during dry conditions (Opfergelt et al., 2006, Geophys. Res. Lett., 33 (15), L15305). The smectite belonged to the beidellite-montmorillonite series. The pervasive presence of water-saturated smectitic clay strongly reduced the permeability in depth, and also altered the rheological and mechanical properties of both the pre-failure rock mass and flow materials. The shrink-swell behavior progressively decreased the rock's shear strength, and gradually destabilized the overlying rock mass in the decades and centuries before the landslide, thereby contributing to slope instability. Prolonged intense rainfall led to the formation of incipient weak failure surfaces in the superficial rock mass. As provoked by water saturation, this process was likely favored by the rapid change of the mechanical properties of smectite-rich clays deposited in fracture, joint and gouge interfaces. We suggest that hazard assessments associated with unstable volcanic slopes, especially on volcanoes hosting a long-lived hydrothermal system, should include the potential long and short-term impacts of swelling clays.

Influence of Radial Stress Gradient on Strainbursts: An Experimental Study

NASA Astrophysics Data System (ADS)

Su, Guoshao; Zhai, Shaobin; Jiang, Jianqing; Zhang, Gangliang; Yan, Liubin

2017-10-01

Strainbursts, which are violent disasters that are accompanied by the ejection failure of rocks, usually occur in hard brittle rocks around highly stressed underground openings. The release of the radial stress at excavation boundaries is one of the major inducing factors for strainbursts in tunnels. After excavation, the radial stress usually exhibits different but apparent gradient variations along the radial direction near the boundary within a certain depth under different in situ stress conditions. In this study, the influence of the radial stress gradient on strainbursts of granite was investigated using an improved true-triaxial rockburst testing system, which was equipped with an acoustic emission monitoring system. The stress state and boundary conditions (i.e., one face free, other faces loaded and increasing tangential stress) of the representative rock element in the vicinity of the excavation boundary were simulated. High-speed cameras were used to capture the ejection failure processes during strainbursts, and the kinetic energy of ejected fragments was quantitatively estimated by analyzing the recorded videos. The experimental results indicate that with an increasing radial stress gradient, the strength increases, the apparent yield platform prior to the peak stress on the stress-strain curves decreases, the failure mode changes from strainburst characterized by tensile splitting to strainburst characterized by shear rupture, and the kinetic energy of ejected fragments during strainbursts significantly increases.

Finite-element modeling of magma chamber-host rock interactions prior to caldera collapse

NASA Astrophysics Data System (ADS)

Kabele, Petr; Žák, Jiří; Somr, Michael

2017-06-01

Gravity-driven failure of shallow magma chamber roofs and formation of collapse calderas are commonly accompanied by ejection of large volumes of pyroclastic material to the Earth's atmosphere and thus represent severe volcanic hazards. In this respect, numerical analysis has proven as a key tool in understanding the mechanical conditions of caldera collapse. The main objective of this paper is to find a suitable approach to finite-element simulation of roof fracturing and caldera collapse during inflation and subsequent deflation of shallow magma chambers. Such a model should capture the dominant mechanical phenomena, for example, interaction of the host rock with magma and progressive deformation of the chamber roof. To this end, a comparative study, which involves various representations of magma (inviscid fluid, nearly incompressible elastic, or plastic solid) and constitutive models of the host rock (fracture and plasticity), was carried out. In particular, the quasi-brittle fracture model of host rock reproduced well the formation of tension-induced radial and circumferential fractures during magma injection into the chamber (inflation stage), especially at shallow crustal levels. Conversely, the Mohr-Coulomb shear criterion has shown to be more appropriate for greater depths. Subsequent magma withdrawal from the chamber (deflation stage) results in further damage or even collapse of the chamber roof. While most of the previous studies of caldera collapse rely on the elastic stress analysis, the proposed approach advances modeling of the process by incorporating non-linear failure phenomena and nearly incompressible behaviour of magma. This leads to a perhaps more realistic representation of the fracture processes preceding roof collapse and caldera formation.

Application of Reservoir Flow Simulation Integrated with Geomechanics in Unconventional Tight Play

NASA Astrophysics Data System (ADS)

Lin, Menglu; Chen, Shengnan; Mbia, Ernest; Chen, Zhangxing

2018-01-01

Multistage hydraulic fracturing techniques, combined with horizontal drilling, have enabled commercial production from the vast reserves of unconventional tight formations. During hydraulic fracturing, fracturing fluid and proppants are pumped into the reservoir matrix to create the hydraulic fractures. Understanding the propagation mechanism of hydraulic fractures is essential to estimate their properties, such as half-length. In addition, natural fractures are often present in tight formations, which might be activated during the fracturing process and contribute to the post-stimulation well production rates. In this study, reservoir simulation is integrated with rock geomechanics to predict the well post-stimulation productivities. Firstly, a reservoir geological model is built based on the field data collected from the Montney formation in the Western Canadian Sedimentary Basin. The hydraulic fracturing process is then simulated through an integrated approach of fracturing fluid injection, rock geomechanics, and tensile failure criteria. In such a process, the reservoir pore pressure increases with a continuous injection of the fracturing fluid and proppants, decreasing the effective stress exerted on the rock matrix accordingly as the overburden pressure remains constant. Once the effective stress drops to a threshold value, tensile failure of the reservoir rock occurs, creating hydraulic fractures in the formation. The early production history of the stimulated well is history-matched to validate the predicted fracture geometries (e.g., half-length) generated from the fracturing simulation process. The effects of the natural fracture properties and well bottom-hole pressures on well productivity are also studied. It has been found that nearly 40% of hydraulic fractures propagate in the beginning stage (the pad step) of the fracturing schedule. In addition, well post-stimulation productivity will increase significantly if the natural fractures are propped or partially propped by the proppants. This paper provides insights on fracture propagation and can be a reference for fracturing treatments in unconventional tight reservoirs.

Semi-analytical and Numerical Studies on the Flattened Brazilian Splitting Test Used for Measuring the Indirect Tensile Strength of Rocks

NASA Astrophysics Data System (ADS)

Huang, Y. G.; Wang, L. G.; Lu, Y. L.; Chen, J. R.; Zhang, J. H.

2015-09-01

Based on the two-dimensional elasticity theory, this study established a mechanical model under chordally opposing distributed compressive loads, in order to perfect the theoretical foundation of the flattened Brazilian splitting test used for measuring the indirect tensile strength of rocks. The stress superposition method was used to obtain the approximate analytic solutions of stress components inside the flattened Brazilian disk. These analytic solutions were then verified through a comparison with the numerical results of the finite element method (FEM). Based on the theoretical derivation, this research carried out a contrastive study on the effect of the flattened loading angles on the stress value and stress concentration degree inside the disk. The results showed that the stress concentration degree near the loading point and the ratio of compressive/tensile stress inside the disk dramatically decreased as the flattened loading angle increased, avoiding the crushing failure near-loading point of Brazilian disk specimens. However, only the tensile stress value and the tensile region were slightly reduced with the increase of the flattened loading angle. Furthermore, this study found that the optimal flattened loading angle was 20°-30°; flattened load angles that were too large or too small made it difficult to guarantee the central tensile splitting failure principle of the Brazilian splitting test. According to the Griffith strength failure criterion, the calculative formula of the indirect tensile strength of rocks was derived theoretically. This study obtained a theoretical indirect tensile strength that closely coincided with existing and experimental results. Finally, this paper simulated the fracture evolution process of rocks under different loading angles through the use of the finite element numerical software ANSYS. The modeling results showed that the Flattened Brazilian Splitting Test using the optimal loading angle could guarantee the tensile splitting failure initiated by a central crack.

Experimental constraints on dynamic fragmentation as a dissipative process during seismic slip.

PubMed

Barber, Troy; Griffith, W Ashley

2017-09-28

Various fault damage fabrics, from gouge in the principal slip zone to fragmented and pulverized rocks in the fault damage zone, have been attributed to brittle deformation at high strain rates during earthquake rupture. Past experimental work has shown that there exists a critical threshold in stress-strain rate space through which rock failure transitions from failure along a few discrete fracture planes to intense fragmentation. We present new experimental results on Arkansas Novaculite (AN) and Westerly Granite (WG) in which we quantify fracture surface area produced by dynamic fragmentation under uniaxial compressive loading and examine the controls of pre-existing mineral anisotropy on dissipative processes at the microscale. Tests on AN produced substantially greater new fracture surface area (approx. 6.0 m 2  g -1 ) than those on WG (0.07 m 2  g -1 ). Estimates of the portion of energy dissipated into brittle fracture were significant for WG (approx. 5%), but appeared substantial in AN (10% to as much as 40%). The results have important implications for the partitioning of dissipated energy under extreme loading conditions expected during earthquakes and the scaling of high-speed laboratory rock mechanics experiments to natural fault zones.This article is part of the themed issue 'Faulting, friction and weakening: from slow to fast motion'. © 2017 The Author(s).

Spectral Characteristics of Continuous Acoustic Emission (AE) Data from Laboratory Rock Deformation Experiments

NASA Astrophysics Data System (ADS)

Flynn, J. William; Goodfellow, Sebastian; Reyes-Montes, Juan; Nasseri, Farzine; Young, R. Paul

2016-04-01

Continuous acoustic emission (AE) data recorded during rock deformation tests facilitates the monitoring of fracture initiation and propagation due to applied stress changes. Changes in the frequency and energy content of AE waveforms have been previously observed and were associated with microcrack coalescence and the induction or mobilisation of large fractures which are naturally associated with larger amplitude AE events and lower-frequency components. The shift from high to low dominant frequency components during the late stages of the deformation experiment, as the rate of AE events increases and the sample approaches failure, indicates a transition from the micro-cracking to macro-cracking regime, where large cracks generated result in material failure. The objective of this study is to extract information on the fracturing process from the acoustic records around sample failure, where the fast occurrence of AE events does not allow for identification of individual AE events and phase arrivals. Standard AE event processing techniques are not suitable for extracting this information at these stages. Instead the observed changes in the frequency content of the continuous record can be used to characterise and investigate the fracture process at the stage of microcrack coalescence and sample failure. To analyse and characterise these changes, a detailed non-linear and non-stationary time-frequency analysis of the continuous waveform data is required. Empirical Mode Decomposition (EMD) and Hilbert Spectral Analysis (HSA) are two of the techniques used in this paper to analyse the acoustic records which provide a high-resolution temporal frequency distribution of the data. In this paper we present the results from our analysis of continuous AE data recorded during a laboratory triaxial deformation experiment using the combined EMD and HSA method.

A theoretical approach to quantify the effect of random cracks on rock deformation in uniaxial compression

NASA Astrophysics Data System (ADS)

Zhou, Shuwei; Xia, Caichu; Zhou, Yu

2018-06-01

Cracks have a significant effect on the uniaxial compression of rocks. Thus, a theoretically analytical approach was proposed to assess the effects of randomly distributed cracks on the effective Young’s modulus during the uniaxial compression of rocks. Each stage of the rock failure during uniaxial compression was analyzed and classified. The analytical approach for the effective Young’s modulus of a rock with only a single crack was derived while considering the three crack states under stress, namely, opening, closure-sliding, and closure-nonsliding. The rock was then assumed to have many cracks with randomly distributed direction, and the effect of crack shape and number during each stage of the uniaxial compression on the effective Young’s modulus was considered. Thus, the approach for the effective Young’s modulus was used to obtain the whole stress-strain process of uniaxial compression. Afterward, the proposed approach was employed to analyze the effects of related parameters on the whole stress-stain curve. The proposed approach was eventually compared with some existing rock tests to validate its applicability and feasibility. The proposed approach has clear physical meaning and shows favorable agreement with the rock test results.

Acceleration to failure in geophysical signals prior to laboratory rock failure and volcanic eruptions (Invited)

NASA Astrophysics Data System (ADS)

Main, I. G.; Bell, A. F.; Greenhough, J.; Heap, M. J.; Meredith, P. G.

2010-12-01

The nucleation processes that ultimately lead to earthquakes, volcanic eruptions, rock bursts in mines, and landslides from cliff slopes are likely to be controlled at some scale by brittle failure of the Earth’s crust. In laboratory brittle deformation experiments geophysical signals commonly exhibit an accelerating trend prior to dynamic failure. Similar signals have been observed prior to volcanic eruptions, including volcano-tectonic earthquake event and moment release rates. Despite a large amount of effort in the search, no such statistically robust systematic trend is found prior to natural earthquakes. Here we describe the results of a suite of laboratory tests on Mount Etna Basalt and other rocks to examine the nature of the non-linear scaling from laboratory to field conditions, notably using laboratory ‘creep’ tests to reduce the boundary strain rate to conditions more similar to those in the field. Seismic event rate, seismic moment release rate and rate of porosity change show a classic ‘bathtub’ graph that can be derived from a simple damage model based on separate transient and accelerating sub-critical crack growth mechanisms, resulting from separate processes of negative and positive feedback in the population dynamics. The signals exhibit clear precursors based on formal statistical model tests using maximum likelihood techniques with Poisson errors. After correcting for the finite loading time of the signal, the results show a transient creep rate that decays as a classic Omori law for earthquake aftershocks, and remarkably with an exponent near unity, as commonly observed for natural earthquake sequences. The accelerating trend follows an inverse power law when fitted in retrospect, i.e. with prior knowledge of the failure time. In contrast the strain measured on the sample boundary shows a less obvious but still accelerating signal that is often absent altogether in natural strain data prior to volcanic eruptions. To test the forecasting power of such constitutive rules in prospective mode, we examine the forecast quality of several synthetic trials, by adding representative statistical fluctuations, due to finite real-time sampling effects, to an underlying accelerating trend. Metrics of forecast quality change systematically and dramatically with time. In particular the model accuracy increases, and the forecast bias decreases, as the failure time approaches.

Modeling rock specimens through 3D printing: Tentative experiments and prospects

NASA Astrophysics Data System (ADS)

Jiang, Quan; Feng, Xiating; Song, Lvbo; Gong, Yahua; Zheng, Hong; Cui, Jie

2016-02-01

Current developments in 3D printing (3DP) technology provide the opportunity to produce rock-like specimens and geotechnical models through additive manufacturing, that is, from a file viewed with a computer to a real object. This study investigated the serviceability of 3DP products as substitutes for rock specimens and rock-type materials in experimental analysis of deformation and failure in the laboratory. These experiments were performed on two types of materials as follows: (1) compressive experiments on printed sand-powder specimens in different shapes and structures, including intact cylinders, cylinders with small holes, and cuboids with pre-existing cracks, and (2) compressive and shearing experiments on printed polylactic acid cylinders and molded shearing blocks. These tentative tests for 3DP technology have exposed its advantages in producing complicated specimens with special external forms and internal structures, the mechanical similarity of its product to rock-type material in terms of deformation and failure, and its precision in mapping shapes from the original body to the trial sample (such as a natural rock joint). These experiments and analyses also successfully demonstrate the potential and prospects of 3DP technology to assist in the deformation and failure analysis of rock-type materials, as well as in the simulation of similar material modeling experiments.

Recent slope failures in the Dolomites (Northeastern Italian Alps) in a context of climate change

NASA Astrophysics Data System (ADS)

Chiarle, Marta; Paranunzio, Roberta; Laio, Francesco; Nigrelli, Guido; Guzzetti, Fausto

2014-05-01

Climate change in the Greater Alpine Region is seriously affecting permafrost distribution, with relevant consequences on slope stability. In the Italian Alps, the number of failures from rockwalls at high elevation markedly increased in the last 20-30 years: the consistent temperature increase, which warmed twice than the global average, may have seriously influenced slope stability, in terms of glaciers retreat and permafrost degradation. Moreover, the growing number of tourists and activities in alpine regions (in particular in the Dolomites) made these areas particularly critical in relation to natural hazards. In this light, an integrated short-term geomorphological and climatic analysis was performed, in order to better comprehend the impact of main climate elements (especially temperature and precipitation) on slope failures in high mountain areas. In this contribution, we focus on three recent slope failures occurred at high elevation sites in the Dolomites (Northeastern Italian Alps), declared a UNESCO World Heritage Site in August 2009. We describe here three important rock falls occurred in the autumn 2013: 1) the Sorapiss rock fall, on 30 September 2013; 2) the Monte Civetta rock fall, on 16 November 2013; 3) the Monte Antelao rock fall, on 22 November 2013. The Monte Civetta rock fall damaged some climbing routes, while the other two landslides did not cause any damage or injury. Despite the limited volume involved, these three events represent an important warning sign in the context of ongoing climate change. Geomorphological information about the rock fall sites were combined with the climatic data acquired from the meteorological stations surrounding the slope failure areas. A short-term climatic analysis was performed, with the aim of understanding the role of the main climatic elements in the triggering of natural instability events in this area and in the Alps in general.

Slow waves moving near the openings in highly stressed conditions

NASA Astrophysics Data System (ADS)

Guzev, Michail; Makarov, Vladimir

2017-04-01

In situ experiments have shown the unusual deformation waves near the openings on high depth of the construction. Process of the wave spreading is beginning after the mining and has two stages of the zonal mesocracking structure formation and development [1]. Extending in a radial direction, the wave poorly fades with distance. For phenomenon modelling the theoretical decision for non-Eucledian models about opening of round cross-section in strongly compressed rock massif is used [2]. The decision qualitatively repeats behaviour of a wave in a rock mass, adjustment of phenomenological parametres is executed. References [1] Vladimir V. Makarov, Mikhail A. Guzev, Vladimir N. Odintsev, Lyudmila S. Ksendzenko (2016) Periodical zonal character of damage near the openings in highly-stressed rock mass conditions. Journal of Rock Mechanics and Geotechnical Engineering. Volume 8, Issue 2, pp. 164-169. [2] M.A. Guzev, V.V. Makarov, 2007. Deforming and failure of the high stressed rocks around the openings, RAS Edit., Vladivostok, 2007, P. 232 (in Russian).

A Description for Rock Joint Roughness Based on Terrestrial Laser Scanner and Image Analysis

PubMed Central

Ge, Yunfeng; Tang, Huiming; Eldin, M. A. M Ez; Chen, Pengyu; Wang, Liangqing; Wang, Jinge

2015-01-01

Shear behavior of rock mass greatly depends upon the rock joint roughness which is generally characterized by anisotropy, scale effect and interval effect. A new index enabling to capture all the three features, namely brightness area percentage (BAP), is presented to express the roughness based on synthetic illumination of a digital terrain model derived from terrestrial laser scanner (TLS). Since only tiny planes facing opposite to shear direction make contribution to resistance during shear failure, therefore these planes are recognized through the image processing technique by taking advantage of the fact that they appear brighter than other ones under the same light source. Comparison with existing roughness indexes and two case studies were illustrated to test the performance of BAP description. The results reveal that the rock joint roughness estimated by the presented description has a good match with existing roughness methods and displays a wider applicability. PMID:26585247

Development of a Unified Rock Bolt Model in Discontinuous Deformation Analysis

NASA Astrophysics Data System (ADS)

He, L.; An, X. M.; Zhao, X. B.; Zhao, Z. Y.; Zhao, J.

2018-03-01

In this paper, a unified rock bolt model is proposed and incorporated into the two-dimensional discontinuous deformation analysis. In the model, the bolt shank is discretized into a finite number of (modified) Euler-Bernoulli beam elements with the degrees of freedom represented at the end nodes, while the face plate is treated as solid blocks. The rock mass and the bolt shank deform independently, but interact with each other through a few anchored points. The interactions between the rock mass and the face plate are handled via general contact algorithm. Different types of rock bolts (e.g., Expansion Shell, fully grouted rebar, Split Set, cone bolt, Roofex, Garford and D-bolt) can be realized by specifying the corresponding constitutive model for the tangential behavior of the anchored points. Four failure modes, namely tensile failure and shear failure of the bolt shank, debonding along the bolt/rock interface and loss of the face plate, are available in the analysis procedure. The performance of a typical conventional rock bolt (fully grouted rebar) and a typical energy-absorbing rock bolt (D-bolt) under the scenarios of suspending loosened blocks and rock dilation is investigated using the proposed model. The reliability of the proposed model is verified by comparing the simulation results with theoretical predictions and experimental observations. The proposed model could be used to reveal the mechanism of each type of rock bolt in realistic scenarios and to provide a numerical way for presenting the detailed profile about the behavior of bolts, in particular at intermediate loading stages.

An Illustration of Determining Quantitatively the Rock Mass Quality Parameters of the Hoek-Brown Failure Criterion

NASA Astrophysics Data System (ADS)

Wu, Li; Adoko, Amoussou Coffi; Li, Bo

2018-04-01

In tunneling, determining quantitatively the rock mass strength parameters of the Hoek-Brown (HB) failure criterion is useful since it can improve the reliability of the design of tunnel support systems. In this study, a quantitative method is proposed to determine the rock mass quality parameters of the HB failure criterion, namely the Geological Strength Index (GSI) and the disturbance factor ( D) based on the structure of drilling core and weathering condition of rock mass combined with acoustic wave test to calculate the strength of rock mass. The Rock Mass Structure Index and the Rock Mass Weathering Index are used to quantify the GSI while the longitudinal wave velocity ( V p) is employed to derive the value of D. The DK383+338 tunnel face of Yaojia tunnel of Shanghai-Kunming passenger dedicated line served as illustration of how the methodology is implemented. The values of the GSI and D are obtained using the HB criterion and then using the proposed method. The measured in situ stress is used to evaluate their accuracy. To this end, the major and minor principal stresses are calculated based on the GSI and D given by HB criterion and the proposed method. The results indicated that both methods were close to the field observation which suggests that the proposed method can be used for determining quantitatively the rock quality parameters, as well. However, these results remain valid only for rock mass quality and rock type similar to those of the DK383+338 tunnel face of Yaojia tunnel.

Relating Seismicity to Dike Emplacement, and the Conundrum of Dyke-Parallel Faulting

NASA Astrophysics Data System (ADS)

Dering, G.; Micklethwaite, S.; Cruden, A. R.; Barnes, S. J.; Fiorentini, M. L.

2016-12-01

Seismic monitoring shows that faulting and fracturing precede and accompany magma emplacement on timescales of hours and days. One outstanding problem is that the precision of earthquake hypocentre locations is typically limited to tens or hundreds of meters and cannot resolve whether the hypocentres relate to strain of wall rock fragments within the dikes, in a process zone around the intrusion or peripherally in the country rock. We examine a swarm of 19 dolerite dikes, near Albany, Western Australia using an unmanned aerial vehicle and Structure-from-Motion photogrammetry to obtain accurate, high resolution 3D reconstructions of outcrop and to digitally extract structural data. We find rare overprinting relationships indicate dike emplacement and faulting was coeval and that the number of faults/fractures increase into the dike swarm (2.2 ± 0.7 more fractures, per unit length in host rocks intruded by dikes relative to the background value). The faults are cataclasite-bearing and parallel to the dikes but intriguingly dike emplacement appears to have been accommodated by mode 1 extension. We further provide the first evidence that dike-parallel shear failure occurs in a damage zone associated with the dike swarm. These results support seismological observations of dike-parallel shear failure associated with some intrusion events, which contradict Mohr-Coulomb theory and numerical modelling of dike propagation in brittle-elastic rock, where shear failure is predicted to occur on faults oriented approximately 30° to the dyke plane. We suggest the dike swarm occupies a network of joints and fractures formed prior to swarm emplacement but then reactivated ahead of propagating dikes and remaining active during the early stages of emplacement.

Mechanical Properties of Shock-Damaged Rocks

NASA Technical Reports Server (NTRS)

He, Hongliang; Ahrens, T. J.

1994-01-01

Stress-strain tests were performed both on shock-damaged gabbro and limestone. The effective Young's modulus decreases with increasing initial damage parameter value, and an apparent work-softening process occurs prior to failure. To further characterize shock-induced microcracks, the longitudinal elastic wave velocity behavior of shock-damaged gabbro in the direction of compression up to failure was measured using an acoustic transmission technique under uniaxial loading. A dramatic increase in velocity was observed for the static compressive stress range of 0-50 MPa. Above that stress range, the velocity behavior of lightly damaged (D(sub 0) less than 0.1) gabbro is almost equal to unshocked gabbro. The failure strength of heavily-damaged (D(sub 0) greater than 0.1) gabbro is approx. 100-150 MPa, much lower than that of lightly damaged and unshocked gabbros (approx. 230-260 MPa). Following Nur's theory, the crack shape distribution was analyzed. The shock-induced cracks in gabbro appear to be largely thin penny-shaped cracks with c/a values below 5 x 10(exp -4). Moreover, the applicability of Ashby and Sammis's theory relating failure strength and damage parameter of shock-damaged rocks was examined and was found to yield a good estimate of the relation of shock-induced deficit in elastic modulus with the deficit in compressive strength.

Rock Slide Risk Assessment: A Semi-Quantitative Approach

NASA Astrophysics Data System (ADS)

Duzgun, H. S. B.

2009-04-01

Rock slides can be better managed by systematic risk assessments. Any risk assessment methodology for rock slides involves identification of rock slide risk components, which are hazard, elements at risk and vulnerability. For a quantitative/semi-quantitative risk assessment for rock slides, a mathematical value the risk has to be computed and evaluated. The quantitative evaluation of risk for rock slides enables comparison of the computed risk with the risk of other natural and/or human-made hazards and providing better decision support and easier communication for the decision makers. A quantitative/semi-quantitative risk assessment procedure involves: Danger Identification, Hazard Assessment, Elements at Risk Identification, Vulnerability Assessment, Risk computation, Risk Evaluation. On the other hand, the steps of this procedure require adaptation of existing or development of new implementation methods depending on the type of landslide, data availability, investigation scale and nature of consequences. In study, a generic semi-quantitative risk assessment (SQRA) procedure for rock slides is proposed. The procedure has five consecutive stages: Data collection and analyses, hazard assessment, analyses of elements at risk and vulnerability and risk assessment. The implementation of the procedure for a single rock slide case is illustrated for a rock slope in Norway. Rock slides from mountain Ramnefjell to lake Loen are considered to be one of the major geohazards in Norway. Lake Loen is located in the inner part of Nordfjord in Western Norway. Ramnefjell Mountain is heavily jointed leading to formation of vertical rock slices with height between 400-450 m and width between 7-10 m. These slices threaten the settlements around Loen Valley and tourists visiting the fjord during summer season, as the released slides have potential of creating tsunami. In the past, several rock slides had been recorded from the Mountain Ramnefjell between 1905 and 1950. Among them, four of the slides caused formation of tsunami waves which washed up to 74 m above the lake level. Two of the slides resulted in many fatalities in the inner part of the Loen Valley as well as great damages. There are three predominant joint structures in Ramnefjell Mountain, which controls failure and the geometry of the slides. The first joint set is a foliation plane striking northeast-southwest and dipping 35˚ -40˚ to the east-southeast. The second and the third joint sets are almost perpendicular and parallel to the mountain side and scarp, respectively. These three joint sets form slices of rock columns with width ranging between 7-10 m and height of 400-450 m. It is stated that the joints in set II are opened between 1-2 m, which may bring about collection of water during heavy rainfall or snow melt causing the slices to be pressed out. It is estimated that water in the vertical joints both reduces the shear strength of sliding plane and causes reduction of normal stress on the sliding plane due to formation of uplift force. Hence rock slides in Ramnefjell mountain occur in plane failure mode. The quantitative evaluation of rock slide risk requires probabilistic analysis of rock slope stability and identification of consequences if the rock slide occurs. In this study failure probability of a rock slice is evaluated by first-order reliability method (FORM). Then in order to use the calculated probability of failure value (Pf) in risk analyses, it is required to associate this Pf with frequency based probabilities (i.ePf / year) since the computed failure probabilities is a measure of hazard and not a measure of risk unless they are associated with the consequences of the failure. This can be done by either considering the time dependent behavior of the basic variables in the probabilistic models or associating the computed Pf with frequency of the failures in the region. In this study, the frequency of previous rock slides in the previous century in Remnefjell is used for evaluation of frequency based probability to be used in risk assessment. The major consequence of a rock slide is generation of a tsunami in the lake Loen, causing inundation of residential areas around the lake. Risk is assessed by adapting damage probability matrix approach, which is originally developed for risk assessment for buildings in case of earthquake.

Influence of porosity and groundmass crystallinity on dome rock strength: a case study from Mt. Taranaki, New Zealand

NASA Astrophysics Data System (ADS)

Zorn, Edgar U.; Rowe, Michael C.; Cronin, Shane J.; Ryan, Amy G.; Kennedy, Lori A.; Russell, James K.

2018-04-01

Lava domes pose a significant hazard to infrastructure, human lives and the environment when they collapse. Their stability is partly dictated by internal mechanical properties. Here, we present a detailed investigation into the lithology and composition of a < 250-year-old lava dome exposed at the summit of Mt. Taranaki in the western North Island of New Zealand. We also examined samples from 400 to 600-year-old block-and-ash flow deposits, formed by the collapse of earlier, short-lived domes extruded at the same vent. Rocks with variable porosity and groundmass crystallinity were compared using measured compressive and tensile strength, derived from deformation experiments performed at room temperature and low (3 MPa) confining pressures. Based on data obtained, porosity exerts the main control on rock strength and mode of failure. High porosity (> 23%) rocks show low rock strength (< 41 MPa) and dominantly ductile failure, whereas lower porosity rocks (5-23%) exhibit higher measured rock strengths (up to 278 MPa) and brittle failure. Groundmass crystallinity, porosity and rock strength are intercorrelated. High groundmass crystal content is inversely related to low porosity, implying crystallisation and degassing of a slowly undercooled magma that experienced rheological stiffening under high pressures deeper within the conduit. This is linked to a slow magma ascent rate and results in a lava dome with higher rock strength. Samples with low groundmass crystallinity are associated with higher porosity and lower rock strength, and represent magma that ascended more rapidly, with faster undercooling, and solidification in the upper conduit at low pressures. Our experimental results show that the inherent strength of rocks within a growing dome may vary considerably depending on ascent/emplacement rates, thus significantly affecting dome stability and collapse hazards.

Real-time forecasting and predictability of catastrophic failure events: from rock failure to volcanoes and earthquakes

NASA Astrophysics Data System (ADS)

Main, I. G.; Bell, A. F.; Naylor, M.; Atkinson, M.; Filguera, R.; Meredith, P. G.; Brantut, N.

2012-12-01

Accurate prediction of catastrophic brittle failure in rocks and in the Earth presents a significant challenge on theoretical and practical grounds. The governing equations are not known precisely, but are known to produce highly non-linear behavior similar to those of near-critical dynamical systems, with a large and irreducible stochastic component due to material heterogeneity. In a laboratory setting mechanical, hydraulic and rock physical properties are known to change in systematic ways prior to catastrophic failure, often with significant non-Gaussian fluctuations about the mean signal at a given time, for example in the rate of remotely-sensed acoustic emissions. The effectiveness of such signals in real-time forecasting has never been tested before in a controlled laboratory setting, and previous work has often been qualitative in nature, and subject to retrospective selection bias, though it has often been invoked as a basis in forecasting natural hazard events such as volcanoes and earthquakes. Here we describe a collaborative experiment in real-time data assimilation to explore the limits of predictability of rock failure in a best-case scenario. Data are streamed from a remote rock deformation laboratory to a user-friendly portal, where several proposed physical/stochastic models can be analysed in parallel in real time, using a variety of statistical fitting techniques, including least squares regression, maximum likelihood fitting, Markov-chain Monte-Carlo and Bayesian analysis. The results are posted and regularly updated on the web site prior to catastrophic failure, to ensure a true and and verifiable prospective test of forecasting power. Preliminary tests on synthetic data with known non-Gaussian statistics shows how forecasting power is likely to evolve in the live experiments. In general the predicted failure time does converge on the real failure time, illustrating the bias associated with the 'benefit of hindsight' in retrospective analyses. Inference techniques that account explicitly for non-Gaussian statistics significantly reduce the bias, and increase the reliability and accuracy, of the forecast failure time in prospective mode.

Observations, models, and mechanisms of failure of surface rocks surrounding planetary surface loads

NASA Technical Reports Server (NTRS)

Schultz, R. A.; Zuber, M. T.

1994-01-01

Geophysical models of flexural stresses in an elastic lithosphere due to an axisymmetric surface load typically predict a transition with increased distance from the center of the load of radial thrust faults to strike-slip faults to concentric normal faults. These model predictions are in conflict with the absence of annular zones of strike-slip faults around prominent loads such as lunar maria, Martian volcanoes, and the Martian Tharsis rise. We suggest that this paradox arises from difficulties in relating failure criteria for brittle rocks to the stress models. Indications that model stresses are inappropriate for use in fault-type prediction include (1) tensile principal stresses larger than realistic values of rock tensile strength, and/or (2) stress differences significantly larger than those allowed by rock-strength criteria. Predictions of surface faulting that are consistent with observations can be obtained instead by using tensile and shear failure criteria, along with calculated stress differences and trajectories, with model stress states not greatly in excess of the maximum allowed by rock fracture criteria.

Optimization of geothermal well trajectory in order to minimize borehole failure

NASA Astrophysics Data System (ADS)

Dahrabou, A.; Valley, B.; Ladner, F.; Guinot, F.; Meier, P.

2017-12-01

In projects based on Enhanced Geothermal System (EGS) principle, deep boreholes are drilled to low permeability rock masses. As part of the completion operations, the permeability of existing fractures in the rock mass is enhanced by injecting large volumes of water. These stimulation treatments aim at achieving enough water circulation for heat extraction at commercial rates which makes the stimulation operations critical to the project success. The accurate placement of the stimulation treatments requires well completion with effective zonal isolation, and wellbore stability is a prerequisite to all zonal isolation techniques, be it packer sealing or cement placement. In this project, a workflow allowing a fast decision-making process for selecting an optimal well trajectory for EGS projects is developed. In fact, the well is first drilled vertically then based on logging data which are costly (100 KCHF/day), the direction in which the strongly deviated borehole section will be drilled needs to be determined in order to optimize borehole stability and to intersect the highest number of fractures that are oriented favorably for stimulation. The workflow applies to crystalline rock and includes an uncertainty and risk assessment framework. An initial sensitivity study was performed to identify the most influential parameters on borehole stability. The main challenge in these analyses is that the strength and stress profiles are unknown independently. Calibration of a geomechanical model on the observed borehole failure has been performed using data from the Basel Geothermal well BS-1. In a first approximation, a purely elastic-static analytical solution in combination with a purely cohesive failure criterion were used as it provides the most consistent prediction across failure indicators. A systematic analysis of the uncertainty on all parameters was performed to assess the reliability of the optimal trajectory selection. To each drilling scenario, failure probability and the associated risks, are computed stochastically. In addition, model uncertainty is assessed by confronting various failure modelling approaches to the available failure data from the Basel Project. Together, these results form the basis of an integrated workflow optimizing geothermal (EGS) well trajectory.

Failure of cap-rock seals as determined from mechanical stratigraphy, stress history, and tensile-failure analysis of exhumed analogs

DOE PAGES

Petrie, E. S.; Evans, J. P.; Bauer, S. J.

2014-11-01

In this study, the sedimentologic and tectonic histories of clastic cap rocks and their inherent mechanical properties control the nature of permeable fractures within them. The migration of fluid through mm- to cm-scale fracture networks can result in focused fluid flow allowing hydrocarbon production from unconventional reservoirs or compromising the seal integrity of fluid traps. To understand the nature and distribution of subsurface fluid-flow pathways through fracture networks in cap-rock seals we examine four exhumed Paleozoic and Mesozoic seal analogs in Utah. We combine these outcrop analyses with subsidence analysis, paleoloading histories, and rock-strength testing data in modified Mohr–Coulomb–Griffith analysesmore » to evaluate the effects of differential stress and rock type on fracture mode.« less

Modelling Coastal Cliff Recession Based on the GIM-DDD Method

NASA Astrophysics Data System (ADS)

Gong, Bin; Wang, Shanyong; Sloan, Scott William; Sheng, Daichao; Tang, Chun'an

2018-04-01

The unpredictable and instantaneous collapse behaviour of coastal rocky cliffs may cause damage that extends significantly beyond the area of failure. Gravitational movements that occur during coastal cliff recession involve two major stages: the small deformation stage and the large displacement stage. In this paper, a method of simulating the entire progressive failure process of coastal rocky cliffs is developed based on the gravity increase method (GIM), the rock failure process analysis method and the discontinuous deformation analysis method, and it is referred to as the GIM-DDD method. The small deformation stage, which includes crack initiation, propagation and coalescence processes, and the large displacement stage, which includes block translation and rotation processes during the rocky cliff collapse, are modelled using the GIM-DDD method. In addition, acoustic emissions, stress field variations, crack propagation and failure mode characteristics are further analysed to provide insights that can be used to predict, prevent and minimize potential economic losses and casualties. The calculation and analytical results are consistent with previous studies, which indicate that the developed method provides an effective and reliable approach for performing rocky cliff stability evaluations and coastal cliff recession analyses and has considerable potential for improving the safety and protection of seaside cliff areas.

Comparison of Crack Initiation, Propagation and Coalescence Behavior of Concrete and Rock Materials

NASA Astrophysics Data System (ADS)

Zengin, Enes; Abiddin Erguler, Zeynal

2017-04-01

There are many previously studies carried out to identify crack initiation, propagation and coalescence behavior of different type of rocks. Most of these studies aimed to understand and predict the probable instabilities on different engineering structures such as mining galleries or tunnels. For this purpose, in these studies relatively smaller natural rock and synthetic rock-like models were prepared and then the required laboratory tests were performed to obtain their strength parameters. By using results provided from these models, researchers predicted the rock mass behavior under different conditions. However, in the most of these studies, rock materials and models were considered as contains none or very few discontinuities and structural flaws. It is well known that rock masses naturally are extremely complex with respect to their discontinuities conditions and thus it is sometimes very difficult to understand and model their physical and mechanical behavior. In addition, some vuggy rock materials such as basalts and limestones also contain voids and gaps having various geometric properties. Providing that the failure behavior of these type of rocks controlled by the crack initiation, propagation and coalescence formed from their natural voids and gaps, the effect of these voids and gaps over failure behavior of rocks should be investigated. Intact rocks are generally preferred due to relatively easy side of their homogeneous characteristics in numerical modelling phases. However, it is very hard to extract intact samples from vuggy rocks because of their complex pore sizes and distributions. In this study, the feasibility of concrete samples to model and mimic the failure behavior vuggy rocks was investigated. For this purpose, concrete samples were prepared at a mixture of %65 cement dust and %35 water and their physical and mechanical properties were determined by laboratory experiments. The obtained physical and mechanical properties were used to constitute numerical models, and then uniaxial compressive strength (UCS) tests were performed on these models by using a commercial software called as Particle Flow Code (PFC2D). When the crack behavior of concrete samples obtained from both laboratory tests and numerical models are compared with the results of previous studies, a significant similarity was found. As a result, due to the observed similarity crack behavior between concretes and rocks, it can be concluded that intact concrete samples can be used for modelling purposes to understand the effect of voids and gaps on failure characteristics of vuggy rocks.

Fault-related clay authigenesis along the Moab Fault: Implications for calculations of fault rock composition and mechanical and hydrologic fault zone properties

USGS Publications Warehouse

Solum, J.G.; Davatzes, N.C.; Lockner, D.A.

2010-01-01

The presence of clays in fault rocks influences both the mechanical and hydrologic properties of clay-bearing faults, and therefore it is critical to understand the origin of clays in fault rocks and their distributions is of great importance for defining fundamental properties of faults in the shallow crust. Field mapping shows that layers of clay gouge and shale smear are common along the Moab Fault, from exposures with throws ranging from 10 to ???1000 m. Elemental analyses of four locations along the Moab Fault show that fault rocks are enriched in clays at R191 and Bartlett Wash, but that this clay enrichment occurred at different times and was associated with different fluids. Fault rocks at Corral and Courthouse Canyons show little difference in elemental composition from adjacent protolith, suggesting that formation of fault rocks at those locations is governed by mechanical processes. Friction tests show that these authigenic clays result in fault zone weakening, and potentially influence the style of failure along the fault (seismogenic vs. aseismic) and potentially influence the amount of fluid loss associated with coseismic dilation. Scanning electron microscopy shows that authigenesis promotes that continuity of slip surfaces, thereby enhancing seal capacity. The occurrence of the authigenesis, and its influence on the sealing properties of faults, highlights the importance of determining the processes that control this phenomenon. ?? 2010 Elsevier Ltd.

Core-log integration for rock mechanics using borehole breakouts and rock strength experiments: Recent results from plate subduction margins

NASA Astrophysics Data System (ADS)

Saito, S.; Lin, W.

2014-12-01

Core-log integration has been applied for rock mechanics studies in scientific ocean drilling since 2007 in plate subduction margins such as Nankai Trough, Costa Rica margin, and Japan Trench. State of stress in subduction wedge is essential for controlling dynamics of plate boundary fault. One of the common methods to estimate stress state is analysis of borehole breakouts (drilling induced borehole wall compressive failures) recorded in borehole image logs to determine the maximum horizontal principal stress orientation. Borehole breakouts can also yield possible range of stress magnitude based on a rock compressive strength criterion. In this study, we constrained the stress magnitudes based on two different rock failure criteria, the Mohr-Coulomb (MC) criteria and the modified Wiebols-Cook (mWC) criteria. As the MC criterion is the same as that under unconfined compression state, only one rock parameter, unconfined compressive strength (UCS) is needed to constrain stress magnitudes. The mWC criterion needs the UCS, Poisson's ratio and internal frictional coefficient determined by triaxial compression experiments to take the intermediate principal stress effects on rock strength into consideration. We conducted various strength experiments on samples taken during IODP Expeditions 334/344 (Costa Rica Seismogenesis Project) to evaluate reliable method to estimate stress magnitudes. Our results show that the effects of the intermediate principal stress on the rock compressive failure occurred on a borehole wall is not negligible.

In situ fragmentation and rock particle sorting on arid hills

NASA Astrophysics Data System (ADS)

McGrath, Gavan S.; Nie, Zhengyao; Dyskin, Arcady; Byrd, Tia; Jenner, Rowan; Holbeche, Georgina; Hinz, Christoph

2013-03-01

Transport processes are often proposed to explain the sorting of rock particles on arid hillslopes, where mean rock particle size often decreases in the downslope direction. Here we show that in situ fragmentation of rock particles can also produce similar patterns. A total of 93,414 rock particles were digitized from 880 photographs of the surface of three mesa hills in the Great Sandy Desert, Australia. Rock particles were characterized by the projected Feret's diameter and circularity. Distance from the duricrust cap was found to be a more robust explanatory variable for diameter than the local hillslope gradient. Mean diameter decreased exponentially downslope, while the fractional area covered by rock particles decreased linearly. Rock particle diameters were distributed lognormally, with both the location and scale parameters decreasing approximately linearly downslope. Rock particle circularity distributions showed little change; only a slight shift in the mode to more circular particles was noted to occur downslope. A dynamic fragmentation model was used to assess whether in situ weathering alone could reproduce the observed downslope fining of diameters. Modeled and observed size distributions agreed well and both displayed a preferential loss of relatively large rock particles and an apparent approach to a terminal size distribution of the rocks downslope. We show this is consistent with a size effect in material strength, where large rocks are more susceptible to fatigue failure under stress than smaller rocks. In situ fragmentation therefore produces qualitatively similar patterns to those that would be expected to arise from selective transport.

A Digital Image-Based Discrete Fracture Network Model and Its Numerical Investigation of Direct Shear Tests

NASA Astrophysics Data System (ADS)

Wang, Peitao; Cai, Meifeng; Ren, Fenhua; Li, Changhong; Yang, Tianhong

2017-07-01

This paper develops a numerical approach to determine the mechanical behavior of discrete fractures network (DFN) models based on digital image processing technique and particle flow code (PFC2D). A series of direct shear tests of jointed rocks were numerically performed to study the effect of normal stress, friction coefficient and joint bond strength on the mechanical behavior of joint rock and evaluate the influence of micro-parameters on the shear properties of jointed rocks using the proposed approach. The complete shear stress-displacement curve of the DFN model under direct shear tests was presented to evaluate the failure processes of jointed rock. The results show that the peak and residual strength are sensitive to normal stress. A higher normal stress has a greater effect on the initiation and propagation of cracks. Additionally, an increase in the bond strength ratio results in an increase in the number of both shear and normal cracks. The friction coefficient was also found to have a significant influence on the shear strength and shear cracks. Increasing in the friction coefficient resulted in the decreasing in the initiation of normal cracks. The unique contribution of this paper is the proposed modeling technique to simulate the mechanical behavior of jointed rock mass based on particle mechanics approaches.

Shale Failure Mechanics and Intervention Measures in Underground Coal Mines: Results From 50 Years of Ground Control Safety Research

PubMed Central

2015-01-01

Ground control research in underground coal mines has been ongoing for over 50 years. One of the most problematic issues in underground coal mines is roof failures associated with weak shale. This paper will present a historical narrative on the research the National Institute for Occupational Safety and Health has conducted in relation to rock mechanics and shale. This paper begins by first discussing how shale is classified in relation to coal mining. Characterizing and planning for weak roof sequences is an important step in developing an engineering solution to prevent roof failures. Next, the failure mechanics associated with the weak characteristics of shale will be discussed. Understanding these failure mechanics also aids in applying the correct engineering solutions. The various solutions that have been implemented in the underground coal mining industry to control the different modes of failure will be summarized. Finally, a discussion on current and future research relating to rock mechanics and shale is presented. The overall goal of the paper is to share the collective ground control experience of controlling roof structures dominated by shale rock in underground coal mining. PMID:26549926

Shale Failure Mechanics and Intervention Measures in Underground Coal Mines: Results From 50 Years of Ground Control Safety Research.

PubMed

Murphy, M M

2016-02-01

Ground control research in underground coal mines has been ongoing for over 50 years. One of the most problematic issues in underground coal mines is roof failures associated with weak shale. This paper will present a historical narrative on the research the National Institute for Occupational Safety and Health has conducted in relation to rock mechanics and shale. This paper begins by first discussing how shale is classified in relation to coal mining. Characterizing and planning for weak roof sequences is an important step in developing an engineering solution to prevent roof failures. Next, the failure mechanics associated with the weak characteristics of shale will be discussed. Understanding these failure mechanics also aids in applying the correct engineering solutions. The various solutions that have been implemented in the underground coal mining industry to control the different modes of failure will be summarized. Finally, a discussion on current and future research relating to rock mechanics and shale is presented. The overall goal of the paper is to share the collective ground control experience of controlling roof structures dominated by shale rock in underground coal mining.

Shale Failure Mechanics and Intervention Measures in Underground Coal Mines: Results From 50 Years of Ground Control Safety Research

NASA Astrophysics Data System (ADS)

Murphy, M. M.

2016-02-01

Ground control research in underground coal mines has been ongoing for over 50 years. One of the most problematic issues in underground coal mines is roof failures associated with weak shale. This paper will present a historical narrative on the research the National Institute for Occupational Safety and Health has conducted in relation to rock mechanics and shale. This paper begins by first discussing how shale is classified in relation to coal mining. Characterizing and planning for weak roof sequences is an important step in developing an engineering solution to prevent roof failures. Next, the failure mechanics associated with the weak characteristics of shale will be discussed. Understanding these failure mechanics also aids in applying the correct engineering solutions. The various solutions that have been implemented in the underground coal mining industry to control the different modes of failure will be summarized. Finally, a discussion on current and future research relating to rock mechanics and shale is presented. The overall goal of the paper is to share the collective ground control experience of controlling roof structures dominated by shale rock in underground coal mining.

Origin, evolution and sedimentary processes associated with a late Miocene submarine landslide, southeast Spain

NASA Astrophysics Data System (ADS)

Sola, F.; Puga-Bernabéu, Á.; Aguirre, J.; Braga, J. C.

2018-02-01

A submarine landslide, the Alhama de Almería Slide, influenced late Tortonian and early Messinian (late Miocene) sedimentary processes in the vicinity of Alhama de Almería in southeast Spain. Its 220-m-high headscarp and deposits are now subaerially exposed. The landslide occurred at the northern slope of the antecedent relief of the present-day Sierra de Gádor mountain range. This is a large antiform trending east-west to east-northeast-west-southwest, which has been uplifting since the late Miocene due to convergence of the African and Eurasian plates. During the Tortonian, this relief was an island separated from the Iberian Peninsula mainland by the Alpujarra corridor, a small and narrow intermontane basin of the Betic Cordillera in the western Mediterranean Sea. The materials involved in the slope failure were Triassic dolostones and phyllites from the metamorphic Alpujárride Complex and Tortonian marine conglomerates, sandstones, and marls that formed an initial sedimentary cover on the basement rocks. Coherent large masses of metamorphic rocks and Miocene deposits at the base of the headscarp distally change to chaotic deposits of blocks of different lithologies embedded in upper Tortonian marine marls, and high-strength cohesive debrites. During downslope sliding, coherent carbonate blocks brecciated due to their greater strength. Phyllites disintegrated, forming a cohesive matrix that engulfed and/or sustained the carbonate blocks. Resedimented, channelized breccias were formed by continuing clast collision, bed fragmentation, and disaggregation of the failed mass. The conditions leading to rock/sediment failure were favoured by steep slopes and weak planes at the contact between the basement carbonates and phyllites. Displacement of collapsed rocks created a canyon-like depression at the southeast edge of the landslide. This depression funnelled sediment gravity flows that were generated upslope, promoting local thick accumulations of sediments during the latest Tortonian-earliest Messinian. The insights from this exposed outcrop have implications for understanding the mechanisms and products of mass-transport deposits on the modern seafloor and the recognition of past failures from subsurface records.

Porosity determination from 2-D resistivity method in studying the slope failures

NASA Astrophysics Data System (ADS)

Maslinda, Umi; Nordiana, M. M.; Bery, A. A.

2017-07-01

Slope failures have become the main focus for infrastructures development on hilly areas in Malaysia especially the development of tourism and residential. Lack of understanding and information of the subsoil conditions and geotechnical issues are the main cause of the slope failures. The failures happened are due to a combination of few factors such as topography, climate, geology and land use. 2-D resistivity method was conducted at the collapsed area in Selangor. The 2-D resistivity was done to study the instability of the area. The collapsed occurred because of the subsurface materials was unstable. Pole-dipole array was used with 5 m minimum electrode spacing for the 2-D resistivity method. The data was processed using Res2Dinv software and the porosity was calculated using Archie's law equation. The results show that the saturated zone (1-100 Ωm), alluvium or highly weathered rock (100-1000 Ωm), boulders (1600-7000 Ωm) and granitic bedrock (>7000 Ωm). Generally, the slope failures or landslides occur during the wet season or after rainfall. It is because of the water infiltrate to the slope and cause the saturation of the slope which can lead to landslides. Then, the porosity of saturated zone is usually high because of the water content. The area of alluvium or highly weathered rock and saturated zone have high porosity (>20%) and the high porosity also dominated at almost all the collapsed area which means that the materials with porosity >20% is potential to be saturated, unstable and might trigger slope failures.

A hazard and risk classification system for catastrophic rock slope failures in Norway

NASA Astrophysics Data System (ADS)

Hermanns, R.; Oppikofer, T.; Anda, E.; Blikra, L. H.; Böhme, M.; Bunkholt, H.; Dahle, H.; Devoli, G.; Eikenæs, O.; Fischer, L.; Harbitz, C. B.; Jaboyedoff, M.; Loew, S.; Yugsi Molina, F. X.

2012-04-01

The Geological Survey of Norway carries out systematic geologic mapping of potentially unstable rock slopes in Norway that can cause a catastrophic failure. As catastrophic failure we describe failures that involve substantial fragmentation of the rock mass during run-out and that impact an area larger than that of a rock fall (shadow angle of ca. 28-32° for rock falls). This includes therefore rock slope failures that lead to secondary effects, such as a displacement wave when impacting a water body or damming of a narrow valley. Our systematic mapping revealed more than 280 rock slopes with significant postglacial deformation, which might represent localities of large future rock slope failures. This large number necessitates prioritization of follow-up activities, such as more detailed investigations, periodic monitoring and permanent monitoring and early-warning. In the past hazard and risk were assessed qualitatively for some sites, however, in order to compare sites so that political and financial decisions can be taken, it was necessary to develop a quantitative hazard and risk classification system. A preliminary classification system was presented and discussed with an expert group of Norwegian and international experts and afterwards adapted following their recommendations. This contribution presents the concept of this final hazard and risk classification that should be used in Norway in the upcoming years. Historical experience and possible future rockslide scenarios in Norway indicate that hazard assessment of large rock slope failures must be scenario-based, because intensity of deformation and present displacement rates, as well as the geological structures activated by the sliding rock mass can vary significantly on a given slope. In addition, for each scenario the run-out of the rock mass has to be evaluated. This includes the secondary effects such as generation of displacement waves or landslide damming of valleys with the potential of later outburst floods. It became obvious that large rock slope failures cannot be evaluated on a slope scale with frequency analyses of historical and prehistorical events only, as multiple rockslides have occurred within one century on a single slope that prior to the recent failures had been inactive for several thousand years. In addition, a systematic analysis on temporal distribution indicates that rockslide activity following deglaciation after the Last Glacial Maximum has been much higher than throughout the Holocene. Therefore the classification system has to be based primarily on the geological conditions on the deforming slope and on the deformation rates and only to a lesser weight on a frequency analyses. Our hazard classification therefore is primarily based on several criteria: 1) Development of the back-scarp, 2) development of the lateral release surfaces, 3) development of the potential basal sliding surface, 4) morphologic expression of the basal sliding surface, 5) kinematic feasibility tests for different displacement mechanisms, 6) landslide displacement rates, 7) change of displacement rates (acceleration), 8) increase of rockfall activity on the unstable rock slope, 9) Presence post-glacial events of similar size along the affected slope and its vicinity. For each of these criteria several conditions are possible to choose from (e.g. different velocity classes for the displacement rate criterion). A score is assigned to each condition and the sum of all scores gives the total susceptibility score. Since many of these observations are somewhat uncertain, the classification system is organized in a decision tree where probabilities can be assigned to each condition. All possibilities in the decision tree are computed and the individual probabilities giving the same total score are summed. Basic statistics show the minimum and maximum total scores of a scenario, as well as the mean and modal value. The final output is a cumulative frequency distribution of the susceptibility scores that can be divided into several classes, which are interpreted as susceptibility classes (very high, high, medium, low, and very low). Today the Norwegian Planning and Building Act uses hazard classes with annual probabilities of impact on buildings producing damages (<1/100, <1/1000, <1/5000 and zero for critical buildings). However, up to now there is not enough scientific knowledge to predict large rock slope failures in these strict classes. Therefore, the susceptibility classes will be matched with the hazard classes from the Norwegian Building Act (e.g. very high susceptibility represents the hazard class with annual probability >1/100). The risk analysis focuses on the potential fatalities of a worst case rock slide scenario and its secondary effects only and is done in consequence classes with a decimal logarithmic scale. However we recommend for all high risk objects that municipalities carry out detailed risk analyses. Finally, the hazard and risk classification system will give recommendations where surveillance in form of continuous 24/7 monitoring systems coupled with early-warning systems (high risk class) or periodic monitoring (medium risk class) should be carried out. These measures are understood as to reduce the risk of life loss due to a rock slope failure close to 0 as population can be evacuated on time if a change of stability situation occurs. The final hazard and risk classification for all potentially unstable rock slopes in Norway, including all data used for its classification will be published within the national landslide database (available on www.skrednett.no).

On the State of Stress and Failure Prediction Near Planetary Surface Loads

NASA Astrophysics Data System (ADS)

Schultz, R. A.

1996-03-01

The state of stress surrounding planetary surface loads has been used extensively to predict failure of surface rocks and to invert this information for effective elastic thickness. As demonstrated previously, however, several factors can be important including an explicit comparison between model stresses and rock strength as well as the magnitude of calculated stress. As re-emphasized below, failure to take stress magnitudes into account can lead to erroneous predictions of near-surface faulting. This abstract results from discussions on graben formation at Fall 1995 AGU.

The Pulse of the Crust: Slow fracture and rapid healing during the seismic cycle (Louis Néel Medal Lecture)

NASA Astrophysics Data System (ADS)

Meredith, Philip

2016-04-01

Earthquake ruptures and volcanic eruptions are the most dramatic manifestations of the dynamic failure of a critically stressed crust. However, these are actually very rare events in both space and time; and most of the crust spends most of its time in a highly stressed but subcritical state. Under upper crustal conditions most rocks accommodate applied stresses in a brittle manner through cracking, fracturing and faulting. Cracks can grow at all scales from the grain scale to the crustal scale, and under different stress regimes. Under tensile stresses, single, long cracks tend to grow at the expense of shorter ones; while under all-round compressive, multiple microcracks tend to coalesce to form macroscopic fractures or faults. Deformation in the crust also occurs over a wide range of strain rates, from the very slow rates associated with tectonic loading up to the very fast rates occurring during earthquake rupture. It is now well-established that reactions between chemically-active pore fluids and the rock matrix can lead to time-dependent, subcritical crack propagation and failure in rocks. In turn, this can allow them to deform and fail over extended periods of time at stresses well below their short-term strength, and even at constant stress; a process known as brittle creep. Such cracking at constant stress eventually leads to accelerated deformation and critical, dynamic failure. However, in the period between sequential dynamic failure events, fractures can become subject to chemically-enhanced time-dependent strength recovery processes such as healing or the growth of mineral veins. We show that such strengthening can be much faster than previously suggested and can occur over geologically very short time-spans. These observations of ultra-slow cracking and ultra-fast healing have profound implications for the evolution and dynamics of the Earth's crust. To obtain a complete understanding of crustal dynamics we require a detailed knowledge of all these time-dependent mechanisms. Such knowledge should be based on micromechanics, but also provide an adequate description at the macroscopic or crustal scale. One way of moving towards this is to establish a relationship between the internal, microstructural state of the rock and the macroscopically observable external quantities. Here, we present a number of examples of attempts to reconcile these ideas through external measurements of stress and strain evolution during deformation with simultaneous measurements of the evolution of key internal variables such as elastic wave speeds, acoustic emission output, porosity and permeability. Overall, the combined data are able to explain both the complexity of stress-strain relations during constant strain rate loading and the shape of creep curves during constant stress loading, thus providing a unifying framework to describe the time-dependent mechanical behaviour of crustal rocks.

A Case Study on the Strata Movement Mechanism and Surface Deformation Regulation in Chengchao Underground Iron Mine

NASA Astrophysics Data System (ADS)

Cheng, Guanwen; Chen, Congxin; Ma, Tianhui; Liu, Hongyuan; Tang, Chunan

2017-04-01

The regular pattern of surface deformation and the mechanism of underground strata movement, especially in iron mines constructed with the block caving method, have a great influence on infrastructure on the surface, so they are an important topic for research. Based on the engineering geology conditions and the surface deformation and fracture features in Chengchao Iron Mine, the mechanism of strata movement and the regular pattern of surface deformation in the footwall were studied by the geomechanical method, and the following conclusions can be drawn: I. The surface deformation process is divided into two stages over time, i.e., the chimney caving development stage and the post-chimney deformation stage. Currently, the surface deformation in Chengchao Iron Mine is at the post-chimney deformation stage. II. At the post-chimney deformation stage, the surface deformation and geological hazards in Chengchao Iron Mine are primarily controlled by the NWW-trending joints, with the phenomenon of toppling deformation and failure on the surface. Based on the surface deformation characteristics in Chengchao Iron Mine, the surface deformation area can be divided into the following four zones: the fracture extension zone, the fracture closure zone, the fracture formation zone and the deformation accumulation zone. The zones on the surface can be determined by the surface deformation characteristics. III. The cantilever beams near the chimney caving area, caused by the NWW-trending joints, have been subjected to toppling failure. This causes the different deformation and failure mechanisms in different locations of the deep rock mass. The deep rock can be divided into four zones, i.e., the fracture zone, fracture transition zone, deformation zone and undisturbed zone, according to the different deformation and failure mechanisms. The zones in the deep rock are the reason for the zones on the surface, so they can be determined by the zones on the surface. Through these findings, the degree of damage to the infrastructure in different locations can be determined based on the surface deformation zones. As the mining continues deeper, the development regulation of the zones on the surface and in deep rock mass can be further studied based on the zones in the deep rock.

Stability analysis of Hawaiian Island flanks using insight gained from strength testing of the HSDP core

NASA Astrophysics Data System (ADS)

Thompson, Nick; Watters, Robert J.; Schiffman, Peter

2008-04-01

Hawaiian Island flank failures are recognized as the largest landslide events on Earth, reaching volumes of several thousand cubic kilometers and lengths of over 200 km and occurring on an average of once every 100 000 years. The 3.1 km deep Hawaii Scientific Drilling Project (HSDP) enabled an investigation of the rock mass strength variations on the island of Hawaii [Schiffman, P., Watters, R.J., Thompson, N., Walton, A.W., 2006. Hyaloclastites and the slope stability of Hawaiian volcanoes: insights from the Hawaiian Scientific Drilling Project's 3-km drill core. Journal of Volcanology and Geothermal Research, 151 (1-3): 217-228]. This study builds on that of Schiffman et al. [Schiffman, P., Watters, R.J., Thompson, N., Walton, A.W., 2006. Hyaloclastites and the slope stability of Hawaiian volcanoes: Insights from the Hawaiian Scientific Drilling Project's 3-km drill core. Journal of Volcanology and Geothermal Research, 151 (1-3): 217-228] by considering more in-depth rock mass classification and strength testing methods of the HSDP core. Geotechnical core logging techniques combined with laboratory strength testing methods show that rock strength differences exist within the edifice. Comparing the rock strength parameters obtained from the various volcano lithologies identified weak zones, suggesting the possible location of future slip surfaces for large flank failures. Relatively weak rock layers were recognized within poorly consolidated hyaloclastite zones, with increases in strength based on degree of alteration. Subaerial and submarine basalt flows are found to be significantly stronger. With the aid of digital elevation models, cross-sections have been developed of key flank areas on the island of Hawaii. Limit equilibrium slope stability analyses are performed on each cross-section using various failure criteria for the rock mass strength calculations. Based on the stability analyses the majority of the slopes analyzed are considered stable. In cases where instability (i.e. failure) is predicted, decreased rock mass quality (strength) of the altered and highly poorly consolidated lithologies is found to have a significant influence. These lithologies are present throughout the Hawaiian Islands, representing potential failure surfaces for large flank collapses. Failure criterion input parameters are considered in sensitivity analyses as are the influences of certain external stability factors such as sea level variation and seismic loading.

Fan-structure wave as a source of earthquake instability

NASA Astrophysics Data System (ADS)

Tarasov, Boris

2015-04-01

Today frictional shear resistance along pre-existing faults is considered to be the lower limit on rock shear strength at confined compression corresponding to the seismogenic layer. This determines the lithospheric strength and the primary earthquake mechanism associated with frictional stick-slip instability on pre-existing faults. This paper introduces a recently identified shear rupture mechanism providing a paradoxical feature of hard rocks - the possibility of shear rupture propagation through the highly confined intact rock mass at shear stress levels significantly less than frictional strength. In the new mechanism the rock failure, associated with consecutive creation of small slabs (known as 'domino-blocks') from the intact rock in the rupture tip, is driven by a fan-shaped domino structure representing the rupture head. The fan-head combines such unique features as: extremely low shear resistance (below the frictional strength), self-sustaining stress intensification in the rupture tip (providing easy formation of new domino-blocks), and self-unbalancing conditions in the fan-head (making the failure process inevitably spontaneous and violent). An important feature of the fan-mechanism is the fact that for the initial formation of the fan-structure an enhanced local shear stress is required, however, after completion of the fan-structure it can propagate as a dynamic wave through intact rock mass at shear stresses below the frictional strength. Paradoxically low shear strength of pristine rocks provided by the fan-mechanism determines the lower limit of the lithospheric strength and favours the generation of new faults in pristine rocks in preference to frictional stick-slip instability along pre-existing faults. The new approach reveals an alternative role of pre-existing faults in earthquake activity: they represent local stress concentrates in pristine rock adjoining the fault where special conditions for the fan-mechanism nucleation are created, while further dynamic propagation of the new fault (earthquake) occurs at low field stresses even below the frictional strength. However, the proximity of the pre-existing discontinuities to the area of instability caused by the fan mechanism creates the illusion of stick-slip instability on the pre-existing faults, thus concealing the real situation.

Recent advances in analysis and prediction of Rock Falls, Rock Slides, and Rock Avalanches using 3D point clouds

NASA Astrophysics Data System (ADS)

Abellan, A.; Carrea, D.; Jaboyedoff, M.; Riquelme, A.; Tomas, R.; Royan, M. J.; Vilaplana, J. M.; Gauvin, N.

2014-12-01

The acquisition of dense terrain information using well-established 3D techniques (e.g. LiDAR, photogrammetry) and the use of new mobile platforms (e.g. Unmanned Aerial Vehicles) together with the increasingly efficient post-processing workflows for image treatment (e.g. Structure From Motion) are opening up new possibilities for analysing, modeling and predicting rock slope failures. Examples of applications at different scales ranging from the monitoring of small changes at unprecedented level of detail (e.g. sub millimeter-scale deformation under lab-scale conditions) to the detection of slope deformation at regional scale. In this communication we will show the main accomplishments of the Swiss National Foundation project "Characterizing and analysing 3D temporal slope evolution" carried out at Risk Analysis group (Univ. of Lausanne) in close collaboration with the RISKNAT and INTERES groups (Univ. of Barcelona and Univ. of Alicante, respectively). We have recently developed a series of innovative approaches for rock slope analysis using 3D point clouds, some examples include: the development of semi-automatic methodologies for the identification and extraction of rock-slope features such as discontinuities, type of material, rockfalls occurrence and deformation. Moreover, we have been improving our knowledge in progressive rupture characterization thanks to several algorithms, some examples include the computing of 3D deformation, the use of filtering techniques on permanently based TLS, the use of rock slope failure analogies at different scales (laboratory simulations, monitoring at glacier's front, etc.), the modelling of the influence of external forces such as precipitation on the acceleration of the deformation rate, etc. We have also been interested on the analysis of rock slope deformation prior to the occurrence of fragmental rockfalls and the interaction of this deformation with the spatial location of future events. In spite of these recent advances, a great challenge still remains in the development of new algorithms for more accurate techniques for 3D point cloud treatment (e.g. filtering, segmentation, etc.) aiming to improve rock slope characterization and monitoring, a series of exciting research findings are expected in the forthcoming years.

The instantaneous rate dependence in low temperature laboratory rock friction and rock deformation experiments

USGS Publications Warehouse

Beeler, N.M.; Tullis, T.E.; Kronenberg, A.K.; Reinen, L.A.

2007-01-01

Earthquake occurrence probabilities that account for stress transfer and time-dependent failure depend on the product of the effective normal stress and a lab-derived dimensionless coefficient a. This coefficient describes the instantaneous dependence of fault strength on deformation rate, and determines the duration of precursory slip. Although an instantaneous rate dependence is observed for fracture, friction, crack growth, and low temperature plasticity in laboratory experiments, the physical origin of this effect during earthquake faulting is obscure. We examine this rate dependence in laboratory experiments on different rock types using a normalization scheme modified from one proposed by Tullis and Weeks [1987]. We compare the instantaneous rate dependence in rock friction with rate dependence measurements from higher temperature dislocation glide experiments. The same normalization scheme is used to compare rate dependence in friction to rock fracture and to low-temperature crack growth tests. For particular weak phyllosilicate minerals, the instantaneous friction rate dependence is consistent with dislocation glide. In intact rock failure tests, for each rock type considered, the instantaneous rate dependence is the same size as for friction, suggesting a common physical origin. During subcritical crack growth in strong quartzofeldspathic and carbonate rock where glide is not possible, the instantaneous rate dependence measured during failure or creep tests at high stress has long been thought to be due to crack growth; however, direct comparison between crack growth and friction tests shows poor agreement. The crack growth rate dependence appears to be higher than the rate dependence of friction and fracture by a factor of two to three for all rock types considered. Copyright 2007 by the American Geophysical Union.

Detecting Slow Deformation Signals Preceding Dynamic Failure: A New Strategy For The Mitigation Of Natural Hazards (SAFER)

NASA Astrophysics Data System (ADS)

Vinciguerra, Sergio; Colombero, Chiara; Comina, Cesare; Ferrero, Anna Maria; Mandrone, Giuseppe; Umili, Gessica; Fiaschi, Andrea; Saccorotti, Gilberto

2014-05-01

Rock slope monitoring is a major aim in territorial risk assessment and mitigation. The high velocity that usually characterizes the failure phase of rock instabilities makes the traditional instruments based on slope deformation measurements not applicable for early warning systems. On the other hand the use of acoustic emission records has been often a good tool in underground mining for slope monitoring. Here we aim to identify the characteristic signs of impending failure, by deploying a "site specific" microseismic monitoring system on an unstable patch of the Madonna del Sasso landslide on the Italian Western Alps designed to monitor subtle changes of the mechanical properties of the medium and installed as close as possible to the source region. The initial characterization based on geomechanical and geophysical tests allowed to understand the instability mechanism and to design the monitoring systems to be placed. Stability analysis showed that the stability of the slope is due to rock bridges. Their failure progress can results in a global slope failure. Consequently the rock bridges potentially generating dynamic ruptures need to be monitored. A first array consisting of instruments provided by University of Turin, has been deployed on October 2013, consisting of 4 triaxial 4.5 Hz seismometers connected to a 12 channel data logger arranged in a 'large aperture' configuration which encompasses the entire unstable rock mass. Preliminary data indicate the occurrence of microseismic swarms with different spectral contents. Two additional geophones and 4 triaxial piezoelectric accelerometers able to operate at frequencies up to 23 KHz will be installed during summer 2014. This will allow us to develop a network capable of recording events with Mw < 0.5 and frequencies between 700 Hz and 20 kHz. Rock physical and mechanical characterization along with rock deformation laboratory experiments during which the evolution of related physical parameters under simulated conditions of stress and fluid content will be also studied and theoretical modelling will allow to come up with a full hazard assessment and test new methodologies for a much wider scale of applications within EU.

Critical Evolution of Damage Toward System-Size Failure in Crystalline Rock

NASA Astrophysics Data System (ADS)

Renard, François; Weiss, Jérôme; Mathiesen, Joachim; Ben-Zion, Yehuda; Kandula, Neelima; Cordonnier, Benoît

2018-02-01

Rock failure under shear loading conditions controls earthquake and faulting phenomena. We study the dynamics of microscale damage precursory to shear faulting in a quartz-monzonite rock representative of crystalline rocks of the continental crust. Using a triaxial rig that is transparent to X-rays, we image the mechanical evolution of centimeter-size core samples by in situ synchrotron microtomography with a resolution of 6.5 μm. Time-lapse three-dimensional images of the samples inside the rig provide a unique data set of microstructural evolution toward faulting. Above a yield point there is a gradual weakening during which microfractures nucleate and grow until this damage span the whole sample. This leads to shear faults oriented about 30° to the main compressive stress in agreement with Anderson's theory and macroscopic failure. The microfractures can be extracted from the three-dimensional images, and their dynamics and morphology (i.e., number, volume, orientation, shape, and largest cluster) are quantified as a function of increasing stress toward failure. The experimental data show for the first time that the total volume of microfractures, the rate of damage growth, and the size of the largest microfracture all increase and diverge when approaching faulting. The average flatness of the microfractures (i.e., the ratio between the second and third eigenvalues of their covariance matrix) shows a significant decrease near failure. The precursors to faulting developing in the future faulting zone are controlled by the evolving microfracture population. Their divergent dynamics toward failure is reminiscent of a dynamical critical transition.

A review of numerical techniques approaching microstructures of crystalline rocks

NASA Astrophysics Data System (ADS)

Zhang, Yahui; Wong, Louis Ngai Yuen

2018-06-01

The macro-mechanical behavior of crystalline rocks including strength, deformability and failure pattern are dominantly influenced by their grain-scale structures. Numerical technique is commonly used to assist understanding the complicated mechanisms from a microscopic perspective. Each numerical method has its respective strengths and limitations. This review paper elucidates how numerical techniques take geometrical aspects of the grain into consideration. Four categories of numerical methods are examined: particle-based methods, block-based methods, grain-based methods, and node-based methods. Focusing on the grain-scale characters, specific relevant issues including increasing complexity of micro-structure, deformation and breakage of model elements, fracturing and fragmentation process are described in more detail. Therefore, the intrinsic capabilities and limitations of different numerical approaches in terms of accounting for the micro-mechanics of crystalline rocks and their phenomenal mechanical behavior are explicitly presented.

Rock slope stability analysis along the North Carolina section of the Blue Ridge Parkway: Using a geographic information system (GIS) to integrate site data and digital geologic maps

USGS Publications Warehouse

Latham, R.S.; Wooten, R.M.; Cattanach, B.L.; Merschat, C.E.; Bozdog, G.N.

2009-01-01

In 2008, the North Carolina Geological Survey (NCGS) completed a five-year geologic and geohazards inventory of the 406-km long North Carolina segment of the Blue Ridge Parkway (BRP). The ArcGIS??? format deliverables for rock slopes include a slope movement and slope movement deposit database and maps and site-specific rock slope stability assessments at 158 locations. Database entries for known and potential rock slope failures include: location data, failure modes and dimensions, activity dates and levels, structural and lithologic data, the occurrence of sulfide minerals and acid-producing potential test results. Rock slope stability assessments include photographs of the rock cuts and show locations and orientations of rock data, seepage zones, and kinematic stability analyses. Assigned preliminary geologic hazard ratings of low, moderate and high indicate the generalized relative probability of rock fall and/or rock slide activity at a given location. Statistics compiled based on the database indicate some general patterns within the data. This information provides the National Park Service with tools that can aid in emergency preparedness, and in budgeting mitigation, maintenance and repair measures. Copyright 2009 ARMA, American Rock Mechanics Association.

Evolution of damage during deformation in porous granular materials (Louis Néel Medal Lecture)

NASA Astrophysics Data System (ADS)

Main, Ian

2014-05-01

'Crackling noise' occurs in a wide variety of systems that respond to external forcing in an intermittent way, leading to sudden bursts of energy release similar to those heard when crunching up a piece of paper or listening to a fire. In mineral magnetism ('Barkhausen') crackling noise occurs due to sudden changes in the size and orientation of microscopic ferromagnetic domains when the external magnetic field is changed. In rock physics sudden changes in internal stress associated with microscopically brittle failure events lead to acoustic emissions that can be recorded on the sample boundary, and used to infer the state of internal damage. Crackling noise is inherently stochastic, but the population of events often exhibits remarkably robust scaling properties, in terms of the source area, duration, energy, and in the waiting time between events. Here I describe how these scaling properties emerge and evolve spontaneously in a fully-dynamic discrete element model of sedimentary rocks subject to uniaxial compression at a constant strain rate. The discrete elements have structural disorder similar to that of a real rock, and this is the only source of heterogeneity. Despite the stationary loading and the lack of any time-dependent weakening processes, the results are all characterized by emergent power law distributions over a broad range of scales, in agreement with experimental observation. As deformation evolves, the scaling exponents change systematically in a way that is similar to the evolution of damage in experiments on real sedimentary rocks. The potential for real-time failure forecasting is examined by using synthetic and real data from laboratory tests and prior to volcanic eruptions. The combination of non-linearity and an irreducible stochastic component leads to significant variations in the precision and accuracy of the forecast failure time, leading to a significant proportion of 'false alarms' (forecast too early) and 'missed events' (forecast too late), as well as an over-optimistic assessments of forecasting power and quality when the failure time is known (the 'benefit of hindsight'). The evolution becomes progressively more complex, and the forecasting power diminishes, in going from ideal synthetics to controlled laboratory tests to open natural systems at larger scales in space and time.

The Role of Tectonic Stress in Triggering Large Silicic Caldera Eruptions

NASA Astrophysics Data System (ADS)

Cabaniss, Haley E.; Gregg, Patricia M.; Grosfils, Eric B.

2018-05-01

We utilize 3-D temperature-dependent viscoelastic finite element models to investigate the mechanical response of the host rock supporting large caldera-size magma reservoirs (volumes >102 km3) to local tectonic stresses. The mechanical stability of the host rock is used to determine the maximum predicted repose intervals and magma flux rates that systems may experience before successive eruption is triggered. Numerical results indicate that regional extension decreases the stability of the roof rock overlying a magma reservoir, thereby promoting early-onset caldera collapse. Alternatively, moderate amounts of compression (≤10 mm/year) on relatively short timescales (<104 years) increases roof rock stability. In addition to quantifying the affect of tectonic stresses on reservoir stability, our models indicate that the process of rejuvenation and mechanical failure is likely to take place over short time periods of hundreds to thousands of years. These findings support the short preeruption melt accumulation timescales indicated by U series disequilibrium studies.

Influence of scale-dependent fracture intensity on block size distribution and rock slope failure mechanisms in a DFN framework

NASA Astrophysics Data System (ADS)

Agliardi, Federico; Galletti, Laura; Riva, Federico; Zanchi, Andrea; Crosta, Giovanni B.

2017-04-01

An accurate characterization of the geometry and intensity of discontinuities in a rock mass is key to assess block size distribution and degree of freedom. These are the main controls on the magnitude and mechanisms of rock slope instabilities (structurally-controlled, step-path or mass failures) and rock mass strength and deformability. Nevertheless, the use of over-simplified discontinuity characterization approaches, unable to capture the stochastic nature of discontinuity features, often hampers a correct identification of dominant rock mass behaviour. Discrete Fracture Network (DFN) modelling tools have provided new opportunities to overcome these caveats. Nevertheless, their ability to provide a representative picture of reality strongly depends on the quality and scale of field data collection. Here we used DFN modelling with FracmanTM to investigate the influence of fracture intensity, characterized on different scales and with different techniques, on the geometry and size distribution of generated blocks, in a rock slope stability perspective. We focused on a test site near Lecco (Southern Alps, Italy), where 600 m high cliffs in thickly-bedded limestones folded at the slope scale impend on the Lake Como. We characterized the 3D slope geometry by Structure-from-Motion photogrammetry (range: 150-1500m; point cloud density > 50 pts/m2). Since the nature and attributes of discontinuities are controlled by brittle failure processes associated to large-scale folding, we performed a field characterization of meso-structural features (faults and related kinematics, vein and joint associations) in different fold domains. We characterized the discontinuity populations identified by structural geology on different spatial scales ranging from outcrops (field surveys and photo-mapping) to large slope sectors (point cloud and photo-mapping). For each sampling domain, we characterized discontinuity orientation statistics and performed fracture mapping and circular window analyses in order to measure fracture intensity (P21) and persistence (trace length distributions). Then, we calibrated DFN models for different combinations of P21/P32 and trace length distributions, characteristic of data collected on different scale. Comparing fracture patterns and block size distributions obtained from different models, we outline the strong influence of field data quality and scale on the rock mass behaviours predicted by DFN. We show that accounting for small scale features (close but short fractures) results in smaller but more interconnected blocks, eventually characterized by low removability and partly supported by intact rock strength. On the other hand, DFN based on data surveyed on slope scale enhance the structural control of persistent fracture on the kinematic degree-of freedom of medium-sized blocks, with significant impacts on the selection and parametrization of rock slope stability modelling approaches.

Stability of rock riprap for protection at the toe of abutments located at the floodplain.

DOT National Transportation Integrated Search

1991-09-01

This report presents the results of a research conducted in a hydraulic flume to : determine the stability of rock riprap protecting abutments located on flood : plains. The observed vulnerable zone for rock riprap failure is presented for : two abut...

Controls on radon emission from granite as evidenced by compression testing to failure

NASA Astrophysics Data System (ADS)

Koike, Katsuaki; Yoshinaga, Tohru; Suetsugu, Kenta; Kashiwaya, Koki; Asaue, Hisafumi

2015-10-01

A set of uniaxial compression tests of granite specimens taken from five localities across Japan was conducted to identify the factors controlling the quantity of radon (Rn) emission (sum of 222Rn and 220Rn) during compression and failure. An α-scintillation detector and a gas flow unit were installed with a testing machine to enable continuous measurement of Rn emissions. Common to all specimens, Rn emissions remained at or slightly declined from the background level after the start of loading; this is similar to the natural phenomenon of decline in groundwater-dissolved Rn before an earthquake. Closure of original microcracks is the most likely cause of the initial Rn decline. Then, Rn emissions begin to increase at 46-57 per cent stress level to the uniaxial compressive strength, and continue to increase even after the failure of specimen. This commencement stress level is close to the general stress level at outbreak of acoustic emissions caused by the development and connection of microcracks. The Rn increase after failure is similar to a phenomenon observed in aftershocks, which may originate from the enhancement of Rn emanations from grains due to the large increase in total surface area and stress release. In addition to the initial radioelement content in rock, the failure pattern (conjugate shear versus longitudinal tensile type), compressive strength, and grain size are possible control factors of the maximum quantity of Rn emissions induced by failure. This maximum may also be affected by the development velocity of the emanation area, which is related to the Rn emanation fraction, associated with the fragmentation. In addition to the magnitude of an earthquake and its hypocentre distance to Rn detectors, the magnitude of increase in Rn concentration in soil gas and groundwater before, during, and after an earthquake in crystalline rocks depends on the intrinsic radioelement content, the mineral texture, and the mechanical properties of rocks. Rock fracturing and failure do not necessarily induce increase in Rn emission due to these rock properties, which can be used to understand the sensitivity of Rn concentration in soil gas or groundwater in connection with an earthquake.

An Experimental Investigation into Failure and Localization Phenomena in the Extension to Shear Fracture Transition in Rock

NASA Astrophysics Data System (ADS)

Choens, R. C., II; Chester, F. M.; Bauer, S. J.; Flint, G. M.

2014-12-01

Fluid-pressure assisted fracturing can produce mesh and other large, interconnected and complex networks consisting of both extension and shear fractures in various metamorphic, magmatic and tectonic systems. Presently, rock failure criteria for tensile and low-mean compressive stress conditions is poorly defined, although there is accumulating evidence that the transition from extension to shear fracture with increasing mean stress is continuous. We report on the results of experiments designed to document failure criteria, fracture mode, and localization phenomena for several rock types (sandstone, limestone, chalk and marble). Experiments were conducted in triaxial extension using a necked (dogbone) geometry to achieve mixed tension and compression stress states with local component-strain measurements in the failure region. The failure envelope for all rock types is similar, but are poorly described using Griffith or modified Griffith (Coulomb or other) failure criteria. Notably, the mode of fracture changes systematically from pure extension to shear with increase in compressive mean stress and display a continuous change in fracture orientation with respect to principal stress axes. Differential stress and inelastic strain show a systematic increase with increasing mean stress, whereas the axial stress decreases before increasing with increasing mean stress. The stress and strain data are used to analyze elastic and plastic strains leading to failure and compare the experimental results to predictions for localization using constitutive models incorporating on bifurcation theory. Although models are able to describe the stability behavior and onset of localization qualitatively, the models are unable to predict fracture type or orientation. Constitutive models using single or multiple yield surfaces are unable to predict the experimental results, reflecting the difficulty in capturing the changing micromechanisms from extension to shear failure. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Deopartment of Energy's National Security Administration under contract DE-AC04-94AL85000. SAND2014-16578A

A study of unstable rock failures using finite difference and discrete element methods

NASA Astrophysics Data System (ADS)

Garvey, Ryan J.

Case histories in mining have long described pillars or faces of rock failing violently with an accompanying rapid ejection of debris and broken material into the working areas of the mine. These unstable failures have resulted in large losses of life and collapses of entire mine panels. Modern mining operations take significant steps to reduce the likelihood of unstable failure, however eliminating their occurrence is difficult in practice. Researchers over several decades have supplemented studies of unstable failures through the application of various numerical methods. The direction of the current research is to extend these methods and to develop improved numerical tools with which to study unstable failures in underground mining layouts. An extensive study is first conducted on the expression of unstable failure in discrete element and finite difference methods. Simulated uniaxial compressive strength tests are run on brittle rock specimens. Stable or unstable loading conditions are applied onto the brittle specimens by a pair of elastic platens with ranging stiffnesses. Determinations of instability are established through stress and strain histories taken for the specimen and the system. Additional numerical tools are then developed for the finite difference method to analyze unstable failure in larger mine models. Instability identifiers are established for assessing the locations and relative magnitudes of unstable failure through measures of rapid dynamic motion. An energy balance is developed which calculates the excess energy released as a result of unstable equilibria in rock systems. These tools are validated through uniaxial and triaxial compressive strength tests and are extended to models of coal pillars and a simplified mining layout. The results of the finite difference simulations reveal that the instability identifiers and excess energy calculations provide a generalized methodology for assessing unstable failures within potentially complex mine models. These combined numerical tools may be applied in future studies to design primary and secondary supports in bump-prone conditions, evaluate retreat mining cut sequences, asses pillar de-stressing techniques, or perform backanalyses on unstable failures in select mining layouts.

Demonstration of a Fractured Rock Geophysical Toolbox (FRGT) for Characterization and Monitoring of DNAPL Biodegradation in Fractured Rock Aquifers

DTIC Science & Technology

2016-01-01

USER’S GUIDE Demonstration of a Fractured Rock Geophysical Toolbox (FRGT) for Characterization and Monitoring of DNAPL Biodegradation in...Toolbox (FRGT) for Characterization and Monitoring of DNAPL Biodegradation in Fractured Rock Aquifers F.D. Day-Lewis, C.D. Johnson, J.H. Williams, C.L...are doomed to failure. DNAPL biodegradation charactrization and monitoring, remediation, fractured rock aquifers. Unclassified Unclassified UU UL 6

The formation and failure of natural dams

USGS Publications Warehouse

Costa, J.E.; Schuster, R.L.

1987-01-01

Of the numerous kinds of dams that form by natural processes, dams formed from landslides, glacial ice, and neoglacial moraines present the greatest threat to people and property. The most common types of mass movements that form landslide dams are rock and debris avalanches, rock and soil slumps and slides, and mud, debris, and earth flows. The most common initiation mechanisms for dam-forming landslides are excessive rainfall and snowmelt and earthquakes. Landslide dams can be classified into six categories based on their relation with the valley floor. Type I dams (11%) of the 81 landslide dams around the world that were classifed do not reach from one valley side to the other. Type II dams (44%) span the entire valley flood, occasionally depositing material high up on opposite valley sides. Type III dams (41%) move considerable distances both upstream and downstream from the landslide failure. Type IV dams (1%) are rare and involve the contemporaneous failure of material from both sides of a valley. Type V dams (1%) are also rare, and are created when a single landslide sends multiple tongues of debris into a valley forming two or more landslide dams in the same surfaces, that extend under the stream or valley and emerge on the opposite valley side. Many landslide dams fail shortly after formation. Overtopping is by far the most common cause of failure. Glacial ice dams can produce at least nine kinds of ice-dammed lakes. The most dangerous are lakes formed in main valleys dammed by tributary glaciers. Failure can occur by erosion of a drainage tunnel under or through the ice dam or by a channel over the ice dam. Cold polar ice dams generally drain supraglacially or marginally by downmelting of an outlet channel. Warmer temperate-ice dams tend to fail by sudden englacial or subglacial breaching and drainage. Late neoglacial moraine-dammed lakes are located in steep mountain areas affected by the advances and retreats of valley glaciers in the last several centuries. The most common reported failure mechanism is overtopping and breaching by a wave or series of waves in the lake, generated by icefalls, rockfalls, or snow or rock avalanches. Melting of ice-cores or frozen ground and piping and seepage are other possible failure mechanisms. (Lantz-PTT)

Coupling photogrammetric data with DFN-DEM model for rock slope hazard assessment

NASA Astrophysics Data System (ADS)

Donze, Frederic; Scholtes, Luc; Bonilla-Sierra, Viviana; Elmouttie, Marc

2013-04-01

Structural and mechanical analyses of rock mass are key components for rock slope stability assessment. The complementary use of photogrammetric techniques [Poropat, 2001] and coupled DFN-DEM models [Harthong et al., 2012] provides a methodology that can be applied to complex 3D configurations. DFN-DEM formulation [Scholtès & Donzé, 2012a,b] has been chosen for modeling since it can explicitly take into account the fracture sets. Analyses conducted in 3D can produce very complex and unintuitive failure mechanisms. Therefore, a modeling strategy must be established in order to identify the key features which control the stability. For this purpose, a realistic case is presented to show the overall methodology from the photogrammetry acquisition to the mechanical modeling. By combining Sirovision and YADE Open DEM [Kozicki & Donzé, 2008, 2009], it can be shown that even for large camera to rock slope ranges (tested about one kilometer), the accuracy of the data are sufficient to assess the role of the structures on the stability of a jointed rock slope. In this case, on site stereo pairs of 2D images were taken to create 3D surface models. Then, digital identification of structural features on the unstable block zone was processed with Sirojoint software [Sirovision, 2010]. After acquiring the numerical topography, the 3D digitalized and meshed surface was imported into the YADE Open DEM platform to define the studied rock mass as a closed (manifold) volume to define the bounding volume for numerical modeling. The discontinuities were then imported as meshed planar elliptic surfaces into the model. The model was then submitted to gravity loading. During this step, high values of cohesion were assigned to the discontinuities in order to avoid failure or block displacements triggered by inertial effects. To assess the respective role of the pre-existing discontinuities in the block stability, different configurations have been tested as well as different degree of fracture persistency in order to enhance the possible contribution of rock bridges on the failure surface development. It is believed that the proposed methodology can bring valuable complementary information for rock slope stability analysis in presence of complex fractured system for which classical "Factor of Safety" is difficult to express. References • Harthong B., Scholtès L. & F.V. Donzé, Strength characterization of rock masses, using a coupled DEM-DFN model, Geophysical Journal International, doi: 10.1111/j.1365-246X.2012.05642.x, 2012. • Kozicki J & Donzé FV. YADE-OPEN DEM: an open--source software using a discrete element method to simulate granular material, Engineering Computations, 26(7):786-805, 2009 • Kozicki J, Donzé FV. A new open-source software developed for numerical simulations using discrete modeling methods, Comp. Meth. In Appl. Mech. And Eng. 197:4429-4443, 2008. • Poropat, G.V., New methods for mapping the structure of rock masses. In Proceedings, Explo 2001, Hunter Valley, New South Wales, 28-31 October 2001, pp. 253-260, 2001. • Scholtès, L. & Donzé FV. Modelling progressive failure in fractured rock masses using a 3D discrete element method, International Journal of Rock Mechanics and Mining Sciences, 52:18-30, 2012a. • Scholtès, L. & Donzé, F.-V., DEM model for soft and hard rocks: role of grain interlocking on strength, J. Mech. Phys. Solids, doi: 10.1016/j.jmps.2012.10.005, 2012b. • Sirovision, Commonwealth Scientific and Industrial Research Organisation CSIRO, Siro3D Sirovision 3D Imaging Mapping System Manual Version 4.1, 2010

Hydromechanical Rock Mass Fatigue in Deep-Seated Landslides Accompanying Seasonal Variations in Pore Pressures

NASA Astrophysics Data System (ADS)

Preisig, Giona; Eberhardt, Erik; Smithyman, Megan; Preh, Alexander; Bonzanigo, Luca

2016-06-01

The episodic movement of deep-seated landslides is often governed by the presence of high pore pressures and reduced effective stresses along active shear surfaces. Pore pressures are subject to cyclic fluctuation under seasonal variations of groundwater recharge, resulting in an intermittent movement characterized by acceleration-deceleration phases. However, it is not always clear why certain acceleration phases reach alarming levels without a clear trigger (i.e., in the absence of an exceptional pore pressure event). This paper presents a conceptual framework linking hydromechanical cycling, progressive failure and fatigue to investigate and explain the episodic behavior of deep-seated landslides using the Campo Vallemaggia landslide in Switzerland as a case study. A combination of monitoring data and advanced numerical modeling is used. The principal processes forcing the slope into a critical disequilibrium state are analyzed as a function of rock mass damage and fatigue. Modeling results suggest that during periods of slope acceleration, the rock slope experiences localized fatigue and gradual weakening through slip along pre-existing natural fractures and yield of critically stressed intact rock bridges. At certain intervals, pockets of critically weakened rock may produce a period of enhanced slope movement in response to a small pore pressure increase similar to those routinely experienced each year. Accordingly, the distribution and connectivity of pre-existing permeable planes of weakness play a central role. These structures are often related to the rock mass's tectonic history or initiate (and dilate) in response to stress changes that disturb the entire slope, such as glacial unloading or seismic loading via large earthquakes. The latter is discussed in detail in a companion paper to this (Gischig et al., Rock Mech Rock Eng, 2015). The results and framework presented further demonstrate that episodic movement and progressive failure of deep-seated landslides cannot be analyzed by means of classical limit equilibrium tools but require advanced numerical models. When calibrated against slope monitoring data, the improved understanding of episodic slope movements can lead to more reliable early warning forecasting and improved landslide hazard management.

Role of Brittle Behaviour of Soft Calcarenites Under Low Confinement: Laboratory Observations and Numerical Investigation

NASA Astrophysics Data System (ADS)

Lollino, Piernicola; Andriani, Gioacchino Francesco

2017-07-01

The strength decay that occurs in the post-peak stage, under low confinement stress, represents a key factor of the stress-strain behaviour of rocks. However, for soft rocks this issue is generally underestimated or even neglected in the solution of boundary value problems, as for example those concerning the stability of underground cavities or rocky cliffs. In these cases, the constitutive models frequently used in limit equilibrium analyses or more sophisticated numerical calculations are, respectively, rigid-plastic or elastic-perfectly plastic. In particular, most of commercial continuum-based numerical codes propose a variety of constitutive models, including elasticity, elasto-plasticity, strain-softening and elasto-viscoplasticity, which are not exhaustive in simulating the progressive failure mechanisms affecting brittle rock materials, these being characterized by material detachment and crack opening and propagation. As a consequence, a numerical coupling with mechanical joint propagation is needed to cope with fracture mechanics. Therefore, continuum-based applications that treat the simulation of the failure processes of intact rock masses at low stress levels may need the adoption of numerical techniques capable of implementing fracture mechanics and rock brittleness concepts, as it is shown in this paper. This work is aimed at highlighting, for some applications of rock mechanics, the essential role of post-peak brittleness of soft rocks by means of the application of a hybrid finite-discrete element method. This method allows for a proper simulation of the brittle rock behaviour and the related mechanism of fracture propagation. In particular, the paper presents two ideal problems, represented by a shallow underground cave and a vertical cliff, for which the evolution of the stability conditions is investigated by comparing the solutions obtained implementing different brittle material responses with those resulting from the assumption of perfectly plastic behaviour. To this purpose, a series of petrophysical and mechanical tests were conducted on samples of soft calcarenite belonging to the Calcarenite di Gravina Fm. (Apulia, Southern Italy), focusing specific attention on the post-peak behaviour of the material under three types of loading (compression, indirect tension and shear). Typical geometrical features representative of real rock engineering problems observed in Southern Italy were assumed in the problems examined. The numerical results indicate the impact of soft rock brittleness in the assessment of stability and highlight the need for the adoption of innovative numerical techniques to analyse these types of problems properly.

The Three-Dimensional (3D) Numerical Stability Analysis of Hyttemalmen Open-Pit

NASA Astrophysics Data System (ADS)

Cała, Marek; Kowalski, Michał; Stopkowicz, Agnieszka

2014-10-01

The purpose of this paper was to perform the 3D numerical calculations allowing slope stability analysis of Hyttemalmen open pit (location Kirkenes, Finnmark Province, Norway). After a ramp rock slide, which took place in December 2010, as well as some other small-scale rock slope stability problems, it proved necessary to perform a serious stability analyses. The Hyttemalmen open pit was designed with a depth up to 100 m, a bench height of 24 m and a ramp width of 10 m. The rock formation in the iron mining district of Kirkenes is called the Bjornevaten Group. This is the most structurally complicated area connected with tectonic process such as folding, faults and metamorphosis. The Bjornevaten Group is a volcano-sedimentary sequence. Rock slope stability depends on the mechanical properties of the rock, hydro-geological conditions, slope topography, joint set systems and seismic activity. However, rock slope stability is mainly connected with joint sets. Joints, or general discontinuities, are regarded as weak planes within rock which have strength reducing consequences with regard to rock strength. Discontinuities within the rock mass lead to very low tensile strength. Several simulations were performed utilising the RocLab (2007) software to estimate the gneiss cohesion for slopes of different height. The RocLab code is dedicated to estimate rock mass strength using the Hoek-Brown failure criterion. Utilising both the GSI index and the Hoek-Brown strength criterion the equivalent Mohr-Coulomb parameters (cohesion and angle of internal friction) can be calculated. The results of 3D numerical calculations (with FLA3D code) show that it is necessary to redesign the slope-bench system in the Hyttemalmen open pit. Changing slope inclination for lower stages is recommended. The minimum factor of safety should be equal 1.3. At the final planned stage of excavation, the factor of safety drops to 1.06 with failure surface ranging through all of the slopes. In the case of a slope angle 70° for lower stages, FS = 1.26, which is not enough to provide slope stability. Another series of calculations were therefore performed taking water table lowering into consideration, which increases the global safety factor. It was finally evaluated, that for a water table level of 72 m the factor of safety equals 1.3, which is enough to assure global open-pit stability.

Development of a new code to solve hydro-mechanical coupling, shear failure and tensile failure due to hydraulic fracturing operations.

NASA Astrophysics Data System (ADS)

María Gómez Castro, Berta; De Simone, Silvia; Carrera, Jesús

2016-04-01

Nowadays, there are still some unsolved relevant questions which must be faced if we want to proceed to the hydraulic fracturing in a safe way. How much will the fracture propagate? This is one of the most important questions that have to be solved in order to avoid the formation of pathways leading to aquifer targets and atmospheric release. Will the fracture failure provoke a microseismic event? Probably this is the biggest fear that people have in fracking. The aim of this work (developed as a part of the EU - FracRisk project) is to understand the hydro-mechanical coupling that controls the shear of existing fractures and their propagation during a hydraulic fracturing operation, in order to identify the key parameters that dominate these processes and answer the mentioned questions. This investigation focuses on the development of a new C++ code which simulates hydro-mechanical coupling, shear movement and propagation of a fracture. The framework employed, called Kratos, uses the Finite Element Method and the fractures are represented with an interface element which is zero thickness. This means that both sides of the element lie together in the initial configuration (it seems a 1D element in a 2D domain, and a 2D element in a 3D domain) and separate as the adjacent matrix elements deform. Since we are working in hard, fragile rocks, we can assume an elastic matrix and impose irreversible displacements in fractures when rock failure occurs. The formulation used to simulate shear and tensile failures is based on the analytical solution proposed by Okada, 1992 and it is part of an iterative process. In conclusion, the objective of this work is to employ the new code developed to analyze the main uncertainties related with the hydro-mechanical behavior of fractures derived from the hydraulic fracturing operations.

Vulnerabilities to Rock-Slope Failure Impacts from Christchurch, NZ Case History Analysis

NASA Astrophysics Data System (ADS)

Grant, A.; Wartman, J.; Massey, C. I.; Olsen, M. J.; Motley, M. R.; Hanson, D.; Henderson, J.

2015-12-01

Rock-slope failures during the 2010/11 Canterbury (Christchurch), New Zealand Earthquake Sequence resulted in 5 fatalities and caused an estimated US$400 million of damage to buildings and infrastructure. Reducing losses from rock-slope failures requires consideration of both hazard (i.e. likelihood of occurrence) and risk (i.e. likelihood of losses given an occurrence). Risk assessment thus requires information on the vulnerability of structures to rock or boulder impacts. Here we present 32 case histories of structures impacted by boulders triggered during the 2010/11 Canterbury earthquake sequence, in the Port Hills region of Christchurch, New Zealand. The consequences of rock fall impacts on structures, taken as penetration distance into structures, are shown to follow a power-law distribution with impact energy. Detailed mapping of rock fall sources and paths from field mapping, aerial lidar digital elevation model (DEM) data, and high-resolution aerial imagery produced 32 well-constrained runout paths of boulders that impacted structures. Impact velocities used for structural analysis were developed using lumped mass 2-D rock fall runout models using 1-m resolution lidar elevation data. Model inputs were based on calibrated surface parameters from mapped runout paths of 198 additional boulder runouts. Terrestrial lidar scans and structure from motion (SfM) imagery generated 3-D point cloud data used to measure structural damage and impacting boulders. Combining velocity distributions from 2-D analysis and high-precision boulder dimensions, kinetic energy distributions were calculated for all impacts. Calculated impact energy versus penetration distance for all cases suggests a power-law relationship between damage and impact energy. These case histories and resulting fragility curve should serve as a foundation for future risk analysis of rock fall hazards by linking vulnerability data to the predicted energy distributions from the hazard analysis.

Results of Microbiologic Investigations of Water-Development Works

DOE Office of Scientific and Technical Information (OSTI.GOV)

Durcheva, V. N., E-mail: durchevavn@vniig.ru; Izmailova, R. A., E-mail: izmailovara@vniig.ru; Legina, E. E., E-mail: leginaee@vniig.ru

2015-03-15

Results are presented for multiyear field investigations of the effect of microbe colonies on components of water-development works. Concrete, metal, and geologic rocks were studied as component parts of the bed of concrete dams functioning in various climatic zones. The participation of lithotrophic bacteria in processes involving corrosion failure of the metal, concrete, and rock beds of dams is established, and causes of intensification of microbe activity are exposed. The need for monitoring the composition and number of microorganisms-biodestructors is substantiated in the water of a reservoir and observation wells, as well as on the surfaces of structural components ofmore » water-development works for monitoring of the safety of the concrete dams.« less

Damage-Based Time-Dependent Modeling of Paraglacial to Postglacial Progressive Failure of Large Rock Slopes

NASA Astrophysics Data System (ADS)

Riva, Federico; Agliardi, Federico; Amitrano, David; Crosta, Giovanni B.

2018-01-01

Large alpine rock slopes undergo long-term evolution in paraglacial to postglacial environments. Rock mass weakening and increased permeability associated with the progressive failure of deglaciated slopes promote the development of potentially catastrophic rockslides. We captured the entire life cycle of alpine slopes in one damage-based, time-dependent 2-D model of brittle creep, including deglaciation, damage-dependent fluid occurrence, and rock mass property upscaling. We applied the model to the Spriana rock slope (Central Alps), affected by long-term instability after Last Glacial Maximum and representing an active threat. We simulated the evolution of the slope from glaciated conditions to present day and calibrated the model using site investigation data and available temporal constraints. The model tracks the entire progressive failure path of the slope from deglaciation to rockslide development, without a priori assumptions on shear zone geometry and hydraulic conditions. Complete rockslide differentiation occurs through the transition from dilatant damage to a compacting basal shear zone, accounting for observed hydraulic barrier effects and perched aquifer formation. Our model investigates the mechanical role of deglaciation and damage-controlled fluid distribution in the development of alpine rockslides. The absolute simulated timing of rock slope instability development supports a very long "paraglacial" period of subcritical rock mass damage. After initial damage localization during the Lateglacial, rockslide nucleation initiates soon after the onset of Holocene, whereas full mechanical and hydraulic rockslide differentiation occurs during Mid-Holocene, supporting a key role of long-term damage in the reported occurrence of widespread rockslide clusters of these ages.

Passive seismic monitoring of natural and induced earthquakes: case studies, future directions and socio-economic relevance

USGS Publications Warehouse

Bohnhoff, Marco; Dresen, Georg; Ellsworth, William L.; Ito, Hisao; Cloetingh, Sierd; Negendank, Jörg

2010-01-01

An important discovery in crustal mechanics has been that the Earth’s crust is commonly stressed close to failure, even in tectonically quiet areas. As a result, small natural or man-made perturbations to the local stress field may trigger earthquakes. To understand these processes, Passive Seismic Monitoring (PSM) with seismometer arrays is a widely used technique that has been successfully applied to study seismicity at different magnitude levels ranging from acoustic emissions generated in the laboratory under controlled conditions, to seismicity induced by hydraulic stimulations in geological reservoirs, and up to great earthquakes occurring along plate boundaries. In all these environments the appropriate deployment of seismic sensors, i.e., directly on the rock sample, at the earth’s surface or in boreholes close to the seismic sources allows for the detection and location of brittle failure processes at sufficiently low magnitude-detection threshold and with adequate spatial resolution for further analysis. One principal aim is to develop an improved understanding of the physical processes occurring at the seismic source and their relationship to the host geologic environment. In this paper we review selected case studies and future directions of PSM efforts across a wide range of scales and environments. These include induced failure within small rock samples, hydrocarbon reservoirs, and natural seismicity at convergent and transform plate boundaries. Each example represents a milestone with regard to bridging the gap between laboratory-scale experiments under controlled boundary conditions and large-scale field studies. The common motivation for all studies is to refine the understanding of how earthquakes nucleate, how they proceed and how they interact in space and time. This is of special relevance at the larger end of the magnitude scale, i.e., for large devastating earthquakes due to their severe socio-economic impact.

A Critical Review of Landslide Failure Mechanisms

NASA Astrophysics Data System (ADS)

Stead, D.; Wolter, A.; Clague, J. J.

2011-12-01

During the last ten years several comprehensive geotechnical studies have been completed on major historic landslides including Randa in Switzerland, Frank in Canada, Aknes in Norway, La Clapiere in France and Vaiont in Italy. In addition, numerous researchers have documented deep-seated gravitational deformations and a wide variety of large prehistoric rock slope failures. The information provided by these studies is evidence of the significant advances made in our ability to map, monitor and model landslides. Over the same period, the mining industry has developed large open pits with slope heights exceeding 1000 m that provide important analogues to high mountain slopes. In this paper we analyse data from the literature to illustrate the importance of brittle fracture, 3D controls, anisotropy, overburden stress, geomorphic processes, groundwater and temperature in major landslides and provide some indicators as to the research required to further understand the complexity of rock slope failure mechanisms. The nature of the landslide failure surface has received inadequate attention in the past, with failure surfaces typically considered in 2D and simulated as discrete, smooth and often planar features. Current work shows that failure surfaces are inherently three-dimensional and have much structural variability across the area of the landslide scarp, reflecting complex structural histories. Such anisotropy and variations may result in multiple events or distinct blocks that move at different rates. Just as most failure surfaces vary spatially, they may also change with depth and thus should more realistically be considered failure zones rather than discrete surfaces. The increasing recognition of the importance of step-path failures, internal dilation and brittle fracture are indicative of the complexity in slope failure surfaces. Related to the variation in failure surface characteristics is the importance of 3D rotational displacements and both the availability and orientation of lateral and rear release surfaces. Accompanying the large increase in the application of numerical models, more consideration needs to be given to both the 3D shape and thickness of major landslides in order to address such questions as: are major landslides symmetric or asymmetric, of limited thickness or deep seated, brittle or ductile?

Processes and mechanisms governing hard rock cliff erosion in western Brittany, France

NASA Astrophysics Data System (ADS)

Laute, Katja; Letortu, Pauline; Le Dantec, Nicolas

2017-04-01

The evolution of rocky coasts is controlled by the interplay between subaerial, marine as well as biological processes, and the geological context. In times of ongoing climate change it is difficult to predict how these erosional landscapes will respond for example to anticipated sea-level rise or to an increase in storminess. However, it can be expected that changes in the morphodynamics of rocky coasts will have a noticeable effect on society and infrastructure. Recent studies have proven that monitoring cliff micro-seismic ground motion has been very effective in exploring both marine and atmospheric actions on coastal cliffs. But only few studies have focused so far on the effects of wave loading and water circulation (runoff, infiltration, water table variations) on cliff stability and subsequent erosion, considering the interaction between subaerial and marine processes. This project focuses on the identification and quantification of environmental controls on hard rock cliff erosion with an emphasis on discriminating the relative contributions of subaerial and marine processes. We aim at relating different sources of mechanical stress (e.g. wave loading, direct wave impact, hydrostatic pressure, thermal expansion) to cliff-scale strain (cliff-top swaying and shaking) and micro-fracturing (generation, expansion and contraction of micro-cracks) with the objective to unravel and discriminate triggering mechanisms of cliff failure. A four-month monitoring field experiment during the winter period (February-May) of 2017 is carried out at a cliff face located in Porsmilin beach (western Brittany, France). The selected cliff section is exposed to Atlantic swell from the south/southwest with a significant wave height of ca. 1.5 m on average and, reaching up to 4 m during storm events. The cliff rises ca. 20 m above the beach and is mainly formed of orthogneiss with intrusions of granodiorite. The entire cliff is highly fractured and altered, which can promote slope failure in the otherwise rather resistant rock. The density of the fracture network and the principal directions of fracturation play a significant role in controlling the rate of mass wasting. The characterization of cliff micro-fracturing will be accomplished through in-situ monitoring of cliff-top ground motion with a seismometer installed at the cliff top and geophones installed within the cliff face. Wave impact will be monitored by setting up a real-time video system in front of the cliff face in combination with pressure- and wave load sensors that will be installed on the beach in a cross-shore array and directly at the cliff toe. Temperature sensors will be placed in shallow boreholes at the cliff face in order to record surface rock temperature. In addition, a weather station and a piezometer will be deployed in order to monitor local weather and groundwater conditions at the study site. This novel combination of the different field measurements is expected to yield new insights into the processes controlling cliff erosion and retreat along rocky coastlines. In particular, we hope to gain understanding on the possible importance of rock micro-fracturing as a precursor to cliff failure.

Investigation on the Cracking Character of Jointed Rock Mass Beneath TBM Disc Cutter

NASA Astrophysics Data System (ADS)

Yang, Haiqing; Liu, Junfeng; Liu, Bolong

2018-04-01

With the purpose to investigate the influence of joint dip angle and spacing on the TBM rock-breaking efficacy and cracking behaviour, experiments that include miniature cutter head tests are carried out on sandstone rock material. In the experiment, prefabricated joints of different forms are made in rock samples. Then theoretical analysis is conducted to improve the calculating models of the fractured work and crack length of rock in the TBM process. The experimental results indicate that lower rupture angles appear for specimens with joint dip angles between 45° and 60°. Meanwhile, rock-breaking efficacy for rock mass with joint dip angles in this interval is also higher. Besides, the fracture patterns are transformed from compressive shear mode to tensile shear mode as the joint spacing decreases. As a result, failure in a greater extent is resulted for specimens with smaller joint spacings. The results above suggest that joint dip angle between 45° and 60° and joint spacing of 1 cm are the optimal rock-breaking conditions for the tested specimens. Combining the present experimental data and taking the joint dip angle and spacing into consideration, the calculating model for rock fractured work that proposed by previous scholars is improved. Finally, theoretical solution of rock median and side crack length is also derived based on the analytical method of elastoplastic invasion fracture for indenter. The result of the analytical solution is also in good agreement with the actual measured experimental result. The present study may provide some primary knowledge about the rock cracking character and breaking efficacy under different engineering conditions.

Detecting Slow Deformation Signals Preceding Dynamic Failure: A New Strategy For The Mitigation Of Natural Hazards (SAFER)

NASA Astrophysics Data System (ADS)

Vinciguerra, Sergio; Colombero, Chiara; Comina, Cesare; Ferrero, Anna Maria; Mandrone, Giuseppe; Umili, Gessica; Fiaschi, Andrea; Saccorotti, Gilberto

2015-04-01

Rock slope monitoring is a major aim in territorial risk assessment and mitigation. The high velocity that usually characterizes the failure phase of rock instabilities makes the traditional instruments based on slope deformation measurements not applicable for early warning systems. The use of "site specific" microseismic monitoring systems, with particular reference to potential destabilizing factors, such as rainfalls and temperature changes, can allow to detect pre-failure signals in unstable sectors within the rock mass and to predict the possible acceleration to the failure. We deployed a microseismic monitoring system in October 2013 developed by the University of Turin/Compagnia San Paolo and consisting of a network of 4 triaxial 4.5 Hz seismometers connected to a 12 channel data logger on an unstable patch of the Madonna del Sasso, Italian Western Alps. The initial characterization based on geomechanical and geophysical tests allowed to understand the instability mechanism and to design a 'large aperture' configuration which encompasses the entire unstable rock and can monitor subtle changes of the mechanical properties of the medium. Stability analysis showed that the stability of the slope is due to rock bridges. A continuous recording at 250 Hz sampling frequency (switched in March 2014 to 1 kHz for improving the first arrival time picking and obtain wider frequency content information) and a trigger recording based on a STA/LTA (Short Time Average over Long Time Average) detection algorithm have been used. More than 2000 events with different waveforms, duration and frequency content have been recorded between November 2013 and March 2014. By inspecting the acquired events we identified the key parameters for a reliable distinction among the nature of each signal, i.e. the signal shape in terms of amplitude, duration, kurtosis and the frequency content in terms of range of maximum frequency content, frequency distribution in spectrograms. Four main classes of recorded signals can be recognised: microseismic events, regional earthquakes, electrical noises and calibration signals, and unclassified events (probably grouping rockfalls, quarry blasts, other anthropic and natural sources of seismic noise). Since the seismic velocity inside the rock mass is highly heterogeneous, as it resulted from the geophysical investigations and the signals are often noisy an accurate location is not possible. To overcome this limitation a three-dimensional P-wave velocity model linking the DSM (Digital Surface Model) of the cliff obtained from a laser-scanner survey to the results of the cross-hole seismic tomography, the geological observations and the geomechanical measures of the most pervasive fracture planes has been built. As a next step we will proceed to the localization of event sources, to the improvement and automation of data analysis procedures and to search for correlations between event rates and meteorological data, for a better understanding of the processes driving the rock mass instability.

Modeling Strain Rate Effect of Heterogeneous Materials Using SPH Method

NASA Astrophysics Data System (ADS)

Ma, G. W.; Wang, X. J.; Li, Q. M.

2010-11-01

The strain rate effect on the dynamic compressive failure of heterogeneous material based on the smoothed particle hydrodynamics (SPH) method is studied. The SPH method employs a rate-insensitive elasto-plastic damage model incorporated with a Weibull distribution law to reflect the mechanical behavior of heterogeneous rock-like materials. A series of simulations are performed for heterogeneous specimens by applying axial velocity conditions, which induce different strain-rate loadings to the specimen. A detailed failure process of the specimens in terms of microscopic crack-activities and the macro-mechanical response are discussed. Failure mechanisms between the low and high strain rate cases are compared. The result shows that the strain-rate effects on the rock strength are mainly caused by the changing internal pressure due to the inertial effects as well as the material heterogeneity. It also demonstrates that the inertial effect becomes significant only when the induced strain rate exceeds a threshold, below which, the dynamic strength enhancement can be explained due to the heterogeneities in the material. It also shows that the dynamic strength is affected more significantly for a relatively more heterogeneous specimen, which coincides with the experimental results showing that the poor quality specimen had a relatively larger increase in the dynamic strength.

"Parco Archeologico Storico Naturale delle Chiese Rupestri del Materano": geomorphological fragility and slope instability in a rupestrian-heritage rich area (Basilicata, south Italy).

NASA Astrophysics Data System (ADS)

Francioso, R.; Sdao, F.; Tropeano, M.

2003-04-01

The Italian Ministry of Education, University and Research financed a research project about the study and the control of hydrogeological hazard of some sites belonging to the "Parco Archeologico Storico Naturale delle Chiese Rupestri del Materano"; the Park and the old city of Matera ("Sassi di Matera") was inserted in the UNESCO World Heritage list since 1993. The studied sites ("Belvedere Chiese Rupestri" and "Iazzo dell'Ofra" localities) are located along the top of the walls of the deep canyon (locally called "Gravina di Matera" and deeper than 100 m) which characterizes the area. Several valuable medieval rupestrian hand-hewn rock churches and sanctuaries are present along the canyon walls. The canyon cut weak rocks (Plio-Pleistocene calcarenites, in which churches and sanctuaries are excavated) and the underlying well-stratified limestones (Cretaceous calcilutites). Both rocks are abundantly and strongly fractured and disjointed by several different joint sets, and, on the left wall of the "Gravina di Matera" canyon, they are characterized by a mainly dipping-slope attitude. Consequently, rock blocks of different sizes formed (up to some tens of m^3 in volume), and are characterized by low stability condition. The considerable acclivity of the walls and the defects and intense fracturing state of rocks, especially along the edge, cause rapid falls, topples and rockslides of the blocks. This geomorphological fragility, confirmed by wide-spread signs of potential instability and by several rock blocks fell in the stream, causes the diffuse and significant structural-failures processes that involve most of the very fine rupestrian heritages. Our study, after the geological and geomorphological description of the sites and the editing of thematic maps, concentrates on the determination the present-day slope instability conditions. Moreover, the study demonstrated the notable genetic relationship between jointing, slope instability and failure type of carbonate blocks. The main results of this geological and geomorphological studies and thematic maps will be reported and discussed.

Elastic-Brittle-Plastic Behaviour of Shale Reservoirs and Its Implications on Fracture Permeability Variation: An Analytical Approach

NASA Astrophysics Data System (ADS)

Masoudian, Mohsen S.; Hashemi, Mir Amid; Tasalloti, Ali; Marshall, Alec M.

2018-05-01

Shale gas has recently gained significant attention as one of the most important unconventional gas resources. Shales are fine-grained rocks formed from the compaction of silt- and clay-sized particles and are characterised by their fissured texture and very low permeability. Gas exists in an adsorbed state on the surface of the organic content of the rock and is freely available within the primary and secondary porosity. Geomechanical studies have indicated that, depending on the clay content of the rock, shales can exhibit a brittle failure mechanism. Brittle failure leads to the reduced strength of the plastic zone around a wellbore, which can potentially result in wellbore instability problems. Desorption of gas during production can cause shrinkage of the organic content of the rock. This becomes more important when considering the use of shales for CO2 sequestration purposes, where CO2 adsorption-induced swelling can play an important role. These phenomena lead to changes in the stress state within the rock mass, which then influence the permeability of the reservoir. Thus, rigorous simulation of material failure within coupled hydro-mechanical analyses is needed to achieve a more systematic and accurate representation of the wellbore. Despite numerous modelling efforts related to permeability, an adequate representation of the geomechanical behaviour of shale and its impact on permeability and gas production has not been achieved. In order to achieve this aim, novel coupled poro-elastoplastic analytical solutions are developed in this paper which take into account the sorption-induced swelling and the brittle failure mechanism. These models employ linear elasticity and a Mohr-Coulomb failure criterion in a plane-strain condition with boundary conditions corresponding to both open-hole and cased-hole completions. The post-failure brittle behaviour of the rock is defined using residual strength parameters and a non-associated flow rule. Swelling and shrinkage are considered to be elastic and are defined using a Langmuir-like curve, which is directly related to the reservoir pressure. The models are used to evaluate the stress distribution and the induced change in permeability within a reservoir. Results show that development of a plastic zone near the wellbore can significantly impact fracture permeability and gas production. The capabilities and limitations of the models are discussed and potential future developments related to modelling of permeability in brittle shales under elastoplastic deformations are identified.

Thermo-hydro-mechanical stresses during repeat glacial cycles as preparatory factors for paraglacial rock slope instabilities

NASA Astrophysics Data System (ADS)

Grämiger, Lorenz; Moore, Jeffrey R.; Gischig, Valentin; Loew, Simon

2015-04-01

Glaciation and deglaciation contribute to stress redistribution in alpine valley rock slopes, generating rock mass damage. However, the physical processes contributing to slope instability during glacial cycles are not well understood, and the mechanical reasoning remains vague. In addition to glacier loading and unloading, thermal strains affect newly exposed bedrock while changes in hillslope hydrology modify effective stresses. Together these can generate damage and reduce rock slope stability over time. Here we explore the role of coupled thermo-hydro-mechanical (THM) stress changes in driving long-term progressive damage and conditioning paraglacial rock slope failure in the Aletsch glacier region of Switzerland. We develop a 2D numerical model using the distinct element code UDEC, creating a fractured rock slope containing rock mass elements of intact rock, discontinuities, and fault zones. Topography, rock properties and glacier history are all loosely based on real conditions in the Aletsch valley. In-situ stresses representing pre-LGM conditions with inherent rock mass damage are initialized. We model stress changes through multiple glacier cycles during the Lateglacial and Holocene; stress redistribution is not only induced by glacier loading, but also by changes in bedrock temperatures and transient hillslope hydrology. Each THM response mechanism is tied to the changing ice extents, therefore stress changes and resulting rock mass damage can be explored in both space and time. We analyze cyclic THM stresses and resulting damage during repeat glacial cycles, and compare spatiotemporal outputs with the mapped landslide distribution in the Aletsch region. Our results extend the concept of glacial debuttressing, lead to improved understanding of the rock mass response to glacial cycles, and clarify coupled interactions driving paraglacial rock mass damage.

Detection of Cracking Levels in Brittle Rocks by Parametric Analysis of the Acoustic Emission Signals

NASA Astrophysics Data System (ADS)

Moradian, Zabihallah; Einstein, Herbert H.; Ballivy, Gerard

2016-03-01

Determination of the cracking levels during the crack propagation is one of the key challenges in the field of fracture mechanics of rocks. Acoustic emission (AE) is a technique that has been used to detect cracks as they occur across the specimen. Parametric analysis of AE signals and correlating these parameters (e.g., hits and energy) to stress-strain plots of rocks let us detect cracking levels properly. The number of AE hits is related to the number of cracks, and the AE energy is related to magnitude of the cracking event. For a full understanding of the fracture process in brittle rocks, prismatic specimens of granite containing pre-existing flaws have been tested in uniaxial compression tests, and their cracking process was monitored with both AE and high-speed video imaging. In this paper, the characteristics of the AE parameters and the evolution of cracking sequences are analyzed for every cracking level. Based on micro- and macro-crack damage, a classification of cracking levels is introduced. This classification contains eight stages (1) crack closure, (2) linear elastic deformation, (3) micro-crack initiation (white patch initiation), (4) micro-crack growth (stable crack growth), (5) micro-crack coalescence (macro-crack initiation), (6) macro-crack growth (unstable crack growth), (7) macro-crack coalescence and (8) failure.

A Coupled Thermal–Hydrological–Mechanical Damage Model and Its Numerical Simulations of Damage Evolution in APSE

PubMed Central

Wei, Chenhui; Zhu, Wancheng; Chen, Shikuo; Ranjith, Pathegama Gamage

2016-01-01

This paper proposes a coupled thermal–hydrological–mechanical damage (THMD) model for the failure process of rock, in which coupling effects such as thermally induced rock deformation, water flow-induced thermal convection, and rock deformation-induced water flow are considered. The damage is considered to be the key factor that controls the THM coupling process and the heterogeneity of rock is characterized by the Weibull distribution. Next, numerical simulations on excavation-induced damage zones in Äspö pillar stability experiments (APSE) are carried out and the impact of in situ stress conditions on damage zone distribution is analysed. Then, further numerical simulations of damage evolution at the heating stage in APSE are carried out. The impacts of in situ stress state, swelling pressure and water pressure on damage evolution at the heating stage are simulated and analysed, respectively. The simulation results indicate that (1) the v-shaped notch at the sidewall of the pillar is predominantly controlled by the in situ stress trends and magnitude; (2) at the heating stage, the existence of confining pressure can suppress the occurrence of damage, including shear damage and tensile damage; and (3) the presence of water flow and water pressure can promote the occurrence of damage, especially shear damage. PMID:28774001

Laboratory investigations into fracture propagation characteristics of rock material

NASA Astrophysics Data System (ADS)

Prasad, B. N. V. Siva; Murthy, V. M. S. R.

2018-04-01

After Industrial Revolution, demand of materials for building up structures have increased enormously. Unfortunately, failures of such structures resulted in loss of life and property. Rock is anisotropic and discontinuous in nature with inherent flaws or so-called discontinuities in it. Rock is apparently used for construction in mining, civil, tunnelling, hydropower, geothermal and nuclear sectors [1]. Therefore, the strength of the structure built up considering rockmass as the construction material needs proper technical evaluation during designing stage itself to prevent and predict the scenarios of catastrophic failures due to these inherent fractures [2]. In this study, samples collected from nine different drilling sites have been investigated in laboratory for understanding the fracture propagation characteristics in rock. Rock material properties, ultrasonic velocities through pulse transmission technique and Mode I Fracture Toughness Testing of different variants of Dolomites and Graywackes are determined in laboratory and the resistance of the rock material to catastrophic crack extension or propagation has been determined. Based on the Fracture Toughness values and the rock properties, critical Energy Release Rates have been estimated. However further studies in this direction is to be carried out to understand the fracture propagation characteristics in three-dimensional space.

Rock Failure Analysis Based on a Coupled Elastoplastic-Logarithmic Damage Model

NASA Astrophysics Data System (ADS)

Abdia, M.; Molladavoodi, H.; Salarirad, H.

2017-12-01

The rock materials surrounding the underground excavations typically demonstrate nonlinear mechanical response and irreversible behavior in particular under high in-situ stress states. The dominant causes of irreversible behavior are plastic flow and damage process. The plastic flow is controlled by the presence of local shear stresses which cause the frictional sliding. During this process, the net number of bonds remains unchanged practically. The overall macroscopic consequence of plastic flow is that the elastic properties (e.g. the stiffness of the material) are insensitive to this type of irreversible change. The main cause of irreversible changes in quasi-brittle materials such as rock is the damage process occurring within the material. From a microscopic viewpoint, damage initiates with the nucleation and growth of microcracks. When the microcracks length reaches a critical value, the coalescence of them occurs and finally, the localized meso-cracks appear. The macroscopic and phenomenological consequence of damage process is stiffness degradation, dilatation and softening response. In this paper, a coupled elastoplastic-logarithmic damage model was used to simulate the irreversible deformations and stiffness degradation of rock materials under loading. In this model, damage evolution & plastic flow rules were formulated in the framework of irreversible thermodynamics principles. To take into account the stiffness degradation and softening on post-peak region, logarithmic damage variable was implemented. Also, a plastic model with Drucker-Prager yield function was used to model plastic strains. Then, an algorithm was proposed to calculate the numerical steps based on the proposed coupled plastic and damage constitutive model. The developed model has been programmed in VC++ environment. Then, it was used as a separate and new constitutive model in DEM code (UDEC). Finally, the experimental Oolitic limestone rock behavior was simulated based on the developed model. The irreversible strains, softening and stiffness degradation were reproduced in the numerical results. Furthermore, the confinement pressure dependency of rock behavior was simulated in according to experimental observations.

Investigation of Rock Mass Stability Around the Tunnels in an Underground Mine in USA Using Three-Dimensional Numerical Modeling

NASA Astrophysics Data System (ADS)

Xing, Yan; Kulatilake, P. H. S. W.; Sandbak, L. A.

2018-02-01

The stability of the rock mass around the tunnels in an underground mine was investigated using the distinct element method. A three-dimensional model was developed based on the available geological, geotechnical, and mine construction information. It incorporates a complex lithological system, persistent and non-persistent faults, and a complex tunnel system including backfilled tunnels. The strain-softening constitutive model was applied for the rock masses. The rock mass properties were estimated using the Hoek-Brown equations based on the intact rock properties and the RMR values. The fault material behavior was modeled using the continuously yielding joint model. Sequential construction and rock supporting procedures were simulated based on the way they progressed in the mine. Stress analyses were performed to study the effect of the horizontal in situ stresses and the variability of rock mass properties on tunnel stability, and to evaluate the effectiveness of rock supports. The rock mass behavior was assessed using the stresses, failure zones, deformations around the tunnels, and the fault shear displacement vectors. The safety of rock supports was quantified using the bond shear and bolt tensile failures. Results show that the major fault and weak interlayer have distinct influences on the displacements and stresses around the tunnels. Comparison between the numerical modeling results and the field measurements indicated the cases with the average rock mass properties, and the K 0 values between 0.5 and 1.25 provide satisfactory agreement with the field measurements.

Direct Shear Tests of Sandstone Under Constant Normal Tensile Stress Condition Using a Simple Auxiliary Device

NASA Astrophysics Data System (ADS)

Cen, Duofeng; Huang, Da

2017-06-01

Tension-shear failure is a typical failure mode in the rock masses in unloading zones induced by excavation or river incision, etc., such as in excavation-disturbed zone of deep underground caverns and superficial rocks of high steep slopes. However, almost all the current shear failure criteria for rock are usually derived on the basis of compression-shear failure. This paper proposes a simple device for use with a servo-controlled compression-shear testing machine to conduct the tension-shear tests of cuboid rock specimens, to test the direct shear behavior of sandstone under different constant normal tensile stress conditions ( σ = -1, -1.5, -2, -2.5 and -3 MPa) as well as the uniaxial tension behavior. Generally, the fracture surface roughness decreases and the proportion of comminution areas in fracture surface increases as the change of stress state from tension to tension-shear and to compression-shear. Stepped fracture is a primary fracture pattern in the tension-shear tests. The shear stiffness, shear deformation and normal deformation (except the normal deformation for σ = -1 MPa) decrease during shearing, while the total normal deformation containing the pre-shearing portion increases as the normal tensile stress level (| σ|) goes up. Shear strength is more sensitive to the normal tensile stress than to the normal compressive stress, and the power function failure criterion (or Mohr envelope form of Hoek-Brown criterion) is examined to be the optimal criterion for the tested sandstone in the full region of tested normal stress in this study.

The role of pore fluids on deforming volcanic rocks: an experimental study

NASA Astrophysics Data System (ADS)

Fazio, Marco; Benson, Philip; Vinciguerra, Sergio; Meredith, Philip

2015-04-01

Pore fluids play an important role on the process of the deformation of rocks. Not only it affects the mechanical properties and the elastic velocities of the material, but it is also responsible in the generation of a whole kind of seismicity, characterized by lower frequency and longer tail (i.e. Long Period, LP, and Hybrid events) than the Volcano-Tectonic (VT) signals, generated by simple shear. While great progress has been made in understanding VT events, LPs, Hybrid signals and the transition between these types of activity are not fully understood yet. This study, aiming in particular on the transition between VT and Hybrid events, shows the results of triaxial experiments on a volcanic rock, run both in dry and wet conditions, to better understand the role of the pore fluids on the final stage of the deformation tests, when the sample is approaching failure. This is achieved through a servo-controlled triaxial testing machine and a state-of the-art acoustic emissions (AEs) kit, composed by an array of 12 piezoelectric sensors surrounding the sample and by both a "triggered" unit, where the events are recorded only if a certain threshold is reached, and a "continuous" unit, where the data is recorded from the beginning to the end of the acquisition, fundamental when the AEs grow exponentially and the triggered unit cannot store at the same rate. The use of sensors of different dominant frequency allows us to better investigate the events occurring as the sample is approaching failure. In both conditions we observe a decrease of the dominant frequency of the seismic activity, due to two different processes: in dry conditions the coalescence of fractures, eventually leading to the major shear zone, creates relatively low-frequency VT events; the same occurs in wet conditions, but the movement of fluids, eased by the merging of the cracks, generates hybrid events. These two type of seismicity are then distinguished in terms of their source mechanism components, where the low-frequency VTs are characterized by a higher DC component, while hybrid events show a greater CLVD one. These results may have a great impacts in the failure forecasting models, not only in volcanic settings, but wherever the pore fluids play an important role on the stability of the rock mass.

Sustained water-level changes caused by damage and compaction induced by teleseismic earthquakes

NASA Astrophysics Data System (ADS)

Shalev, Eyal; Kurzon, Ittai; Doan, Mai-Linh; Lyakhovsky, Vladimir

2016-07-01

Sustained water-level increase and decrease induced by distant earthquakes were observed in two wells, Gomè 1 and Meizar 1 in Israel. The Gomè 1 well is located within a damage zone of a major fault zone, and Meizar 1 is relatively far from a fault. The monitored pressure change in both wells shows significant water-level oscillations and sustained water-level changes in response to the passage of the seismic waves. The sustained water-level changes include short-term (minutes) undrained behavior and longer-period (hours and days) drained behavior associated with groundwater flow. We model the short-term undrained response of water pressure oscillations and sustained change to the distant 2013 Mw 7.7 Balochistan earthquake by nonlinear elastic behavior of damaged rocks, accounting for small wave-induced compaction and damage accumulation. We suggest that the rocks are close to failure in both locations and strain oscillations produced by the passing seismic waves periodically push the rock above the yield cap, creating compaction when volumetric strain increases and damage when shear strain increases. Compaction increases pore pressure, whereas damage accumulation decreases pore pressure by fracture dilation. The dominant process depends on the properties of the rock. For highly damaged rocks, dilatancy is dominant and a sustained pressure decrease is expected. For low-damage rocks, compaction is the dominant process creating sustained water-level increase. We calculate damage and porosity changes associated to the Balochistan earthquake in both wells and quantify damage accumulation and compaction during the passage of the seismic waves.

Precursory seismicity associated with frequent, large ice avalanches on Iliamna Volcano, Alaska, USA

USGS Publications Warehouse

Caplan-Auerbach, Jacqueline; Huggel, C.

2007-01-01

Since 1994, at least six major (volume>106 m3) ice and rock avalanches have occurred on Iliamna volcano, Alaska, USA. Each of the avalanches was preceded by up to 2 hours of seismicity believed to represent the initial stages of failure. Each seismic sequence begins with a series of repeating earthquakes thought to represent slip on an ice-rock interface, or between layers of ice. This stage is followed by a prolonged period of continuous ground-shaking that reflects constant slip accommodated by deformation at the glacier base. Finally the glacier fails in a large avalanche. Some of the events appear to have entrained large amounts of rock, while others comprise mostly snow and ice. Several avalanches initiated from the same source region, suggesting that this part of the volcano is particularly susceptible to failure, possibly due to the presence of nearby fumaroles. Although thermal conditions at the time of failure are not well constrained, it is likely that geothermal energy causes melting at the glacier base, promoting slip and culminating in failure. The frequent nature and predictable failure sequence of Iliamna avalanches makes the volcano an excellent laboratory for the study of ice avalanches. The prolonged nature of the seismic signal suggests that warning may one day be given for similar events occurring in populated regions.

Rock slope instabilities in Norway: First systematic hazard and risk classification of 22 unstable rock slopes

NASA Astrophysics Data System (ADS)

Böhme, Martina; Hermanns, Reginald L.; Oppikofer, Thierry; Penna, Ivanna

2016-04-01

Unstable rock slopes that can cause large failures of the rock-avalanche type have been mapped in Norway for almost two decades. Four sites have earlier been characterized as high-risk objects based on expertise of few researchers. This resulted in installing continuous monitoring systems and set-up of an early-warning system for those four sites. Other unstable rock slopes have not been ranked related to their hazard or risk. There are ca. 300 other sites known of which 70 sites were installed for periodic deformation measurements using multiple techniques (Global Navigation Satellite Systems, extensometers, measurement bolts, and others). In 2012 a systematic hazard and risk classification system for unstable rock slopes was established in Norway and the mapping approach adapted to that in 2013. Now, the first 22 sites were classified for hazard, consequences and risk using this classification system. The selection of the first group of sites to be classified was based on an assumed high hazard or risk and importance given to the sites by Norwegian media and the public. Nine of the classified 22 unstable rock slopes are large sites that deform inhomogeneously or are strongly broken up in individual blocks. This suggests that different failure scenarios are possible that need to be analyzed individually. A total of 35 failure scenarios for those nine unstable rock slopes were considered. The hazard analyses were based on 9 geological parameters defined in the classification system. The classification system will be presented based on the Gamanjunni unstable rock slope. This slope has a well developed back scarp that exposes 150 m preceding displacement. The lateral limits of the unstable slope are clearly visible in the morphology and InSAR displacement data. There have been no single structures observed that allow sliding kinematically. The lower extend of the displacing rock mass is clearly defined in InSAR data and by a zone of higher rock fall activity. Yearly average displacement rates of up to 6 cm are measured with differential GNSS and InSAR. Cosmogenic nuclide dating suggests an acceleration of the present displacement compared to the average displacement since the initiation of the gravitational movement approximately 7000 years ago. Furthermore, there exists a pre-historic rock avalanche 3 km north along the same slope. These characteristics result in a very high hazard for the Gamanjunni unstable rock slope. The consequence analyses focus on the possibility of life loss only. For this the number of persons in the area that can be affected by either the rock slope failure itself and/or its secondary consequence of a displacement wave in case that a rock slope failure would hit a water body is estimated. For Gamanjunni the direct consequences are approximately 40 casualties, representing medium consequences. A total of 48 scenarios were finally analyzed for hazard, consequences and risk. The results are plotted in a risk matrix with 5 hazard and 5 consequence classes, leading to 4 risk classes. One unstable rock slope was classified as very high hazard, 9 scenarios as high hazard, 25 as medium hazard and 13 as low hazard, while none were classified as very low hazard. The consequence analyses for those scenarios resulted in 5 scenarios with very high consequences (>1000 potential casualties), 13 scenarios with high consequences (100-1000 casualties), 9 scenarios with medium consequences (10-100 casualties), 6 scenarios with low consequences (1-10 casualties) and 15 scenarios with very low consequences (0-1 casualties). This resulted in a high risk for 6 scenarios, medium to high risk for 16 scenarios, medium risk for 7 scenarios and low risk for 19 scenarios. These results allow determining which unstable rock slopes do not require further follow-up and on which further investigations and/or mitigation measures should be considered.

Rock falls from Glacier Point above Camp Curry, Yosemite National Park, California

USGS Publications Warehouse

Wieczorek, Gerald F.; Snyder, James B.

1999-01-01

A series of rock falls from the north face of Glacier Point above Camp Curry, Yosemite National Park, California, have caused reexamination of the rock-fall hazard because beginning in June, 1999 a system of cracks propagated through a nearby rock mass outlining a future potential rock fall. If the estimated volume of the potential rock fall fails as a single piece, there could be a risk from rock-fall impact and airborne rock debris to cabins in Camp Curry. The role of joint plane orientation and groundwater pressure in the fractured rock mass are discussed in light of the pattern of developing cracks and potential modes of failure.

Fracture Energy-Based Brittleness Index Development and Brittleness Quantification by Pre-peak Strength Parameters in Rock Uniaxial Compression

NASA Astrophysics Data System (ADS)

Munoz, H.; Taheri, A.; Chanda, E. K.

2016-12-01

Brittleness is a fundamental mechanical rock property critical to many civil engineering works, mining development projects and mineral exploration operations. However, rock brittleness is a concept yet to be investigated as there is not any unique criterion available, widely accepted by rock engineering community able to describe rock brittleness quantitatively. In this study, new brittleness indices were developed based on fracture strain energy quantities obtained from the complete stress-strain characteristics of rocks. In doing so, different rocks having unconfined compressive strength values ranging from 7 to 215 MPa were examined in a series of quasi-static uniaxial compression tests after properly implementing lateral-strain control in a closed-loop system to apply axial load to rock specimen. This testing method was essential to capture post-peak regime of the rocks since a combination of class I-II or class II behaviour featured post-peak stress-strain behaviour. Further analysis on the post-peak strain localisation, stress-strain characteristics and the fracture pattern causing class I-II and class II behaviour were undertaken by analysing the development of field of strains in the rocks via three-dimensional digital image correlation. Analysis of the results demonstrated that pre-peak stress-strain brittleness indices proposed solely based on pre-peak stress-strain behaviour do not show any correlation with any of pre-peak rock mechanical parameters. On the other hand, the proposed brittleness indices based on pre-peak and post-peak stress-strain relations were found to competently describe an unambiguous brittleness scale against rock deformation and strength parameters such as the elastic modulus, the crack damage stress and the peak stress relevant to represent failure process.

Fracture and compaction of andesite in a volcanic edifice.

PubMed

Heap, M J; Farquharson, J I; Baud, P; Lavallée, Y; Reuschlé, T

The failure mode of lava-dilatant or compactant-depends on the physical attributes of the lava, primarily the porosity and pore size, and the conditions under which it deforms. The failure mode for edifice host rock has attendant implications for the structural stability of the edifice and the efficiency of the sidewall outgassing of the volcanic conduit. In this contribution, we present a systematic experimental study on the failure mode of edifice-forming andesitic rocks (porosity from 7 to 25 %) from Volcán de Colima, Mexico. The experiments show that, at shallow depths (<1 km), both low- and high-porosity lavas dilate and fail by shear fracturing. However, deeper in the edifice (>1 km), while low-porosity (<10 %) lava remains dilatant, the failure of high-porosity lava is compactant and driven by cataclastic pore collapse. Although inelastic compaction is typically characterised by the absence of strain localisation, we observe compactive localisation features in our porous andesite lavas manifest as subplanar surfaces of collapsed pores. In terms of volcano stability, faulting in the upper edifice could destabilise the volcano, leading to an increased risk of flank or large-scale dome collapse, while compactant deformation deeper in the edifice may emerge as a viable mechanism driving volcano subsidence, spreading and destabilisation. The failure mode influences the evolution of rock physical properties: permeability measurements demonstrate that a throughgoing tensile fracture increases sample permeability (i.e. equivalent permeability) by about a factor of two, and that inelastic compaction to an axial strain of 4.5 % reduces sample permeability by an order of magnitude. The implication of these data is that sidewall outgassing may therefore be efficient in the shallow edifice, where rock can fracture, but may be impeded deeper in the edifice due to compaction. The explosive potential of a volcano may therefore be subject to increase over time if the progressive compaction and permeability reduction in the lower edifice cannot be offset by the formation of permeable fracture pathways in the upper edifice. The mode of failure of the edifice host rock is therefore likely to be an important factor controlling lateral outgassing and thus eruption style (effusive versus explosive) at stratovolcanoes.

Aquifer characteristics near cuestas and their relation to rock tensile strength

USGS Publications Warehouse

Morin, Roger H.; Schulz, William; LoCoco, James

2010-01-01

Along the northeast coast of North America, extensional tectonic processes have generated lithologic and topographic features that are common to several rift basins. A cap of igneous rock overlies sedimentary rock to form a cuesta with both rock types exposed along a steep ridge flank. Field studies investigating the near‐surface hydrogeologic properties of the caprocks at several of these sites have reported a narrow range of results; some fractured rocks form modest aquifers whereas others do not. To examine this behavior in terms of geomechanical responses to gravitational stresses imposed near ridges, a finite‐element model is presented that incorporates the geometry of a ridge‐valley configuration and its major structural elements. Model simulations reflect the effects of a lack of buttressing along free faces and a contrast in Poisson's ratios between the superposed igneous and sedimentary rocks. Three‐dimensional Mohr's circles are constructed from principal stress magnitudes and directions to evaluate the response of individual fracture planes to this stress state. Results depict a predominantly tensional stress environment where numerous pre‐existing fractures may be favorably aligned for opening and enhanced caprock permeability. However, the lack of conclusive field evidence to support this hypothesis suggests that the in situ tensile strength of the fractured rock mass is substantial enough to resist failure by shear or dilation, and that critically‐stressed fracture planes do not convey large volumes of groundwater in ridge‐valley settings.

Landslides - Cause and effect

USGS Publications Warehouse

Radbruch-Hall, D. H.; Varnes, D.J.

1976-01-01

Landslides can cause seismic disturbances; landslides can also result from seismic disturbances, and earthquake-induced slides have caused loss of life in many countries. Slides can cause disastrous flooding, particularly when landslide dams across streams are breached, and flooding may trigger slides. Slope movement in general is a major process of the geologic environment that places constraints on engineering development. In order to understand and foresee both the causes and effects of slope movement, studies must be made on a regional scale, at individual sites, and in the laboratory. Areal studies - some embracing entire countries - have shown that certain geologic conditions on slopes facilitate landsliding; these conditions include intensely sheared rocks; poorly consolidated, fine-grained clastic rocks; hard fractured rocks underlain by less resistant rocks; or loose accumulations of fine-grained surface debris. Field investigations as well as mathematical- and physical-model studies are increasing our understanding of the mechanism of slope movement in fractured rock, and assist in arriving at practical solutions to landslide problems related to all kinds of land development for human use. Progressive failure of slopes has been studied in both soil and rock mechanics. New procedures have been developed to evaluate earthquake response of embankments and slopes. The finite element method of analysis is being extensively used in the calculation of slope stability in rock broken by joints, faults, and other discontinuities. ?? 1976 International Association of Engineering Geology.

Rockfall hazard and risk assessments along roads at a regional scale: example in Swiss Alps

NASA Astrophysics Data System (ADS)

Michoud, C.; Derron, M.-H.; Horton, P.; Jaboyedoff, M.; Baillifard, F.-J.; Loye, A.; Nicolet, P.; Pedrazzini, A.; Queyrel, A.

2012-03-01

Unlike fragmental rockfall runout assessments, there are only few robust methods to quantify rock-mass-failure susceptibilities at regional scale. A detailed slope angle analysis of recent Digital Elevation Models (DEM) can be used to detect potential rockfall source areas, thanks to the Slope Angle Distribution procedure. However, this method does not provide any information on block-release frequencies inside identified areas. The present paper adds to the Slope Angle Distribution of cliffs unit its normalized cumulative distribution function. This improvement is assimilated to a quantitative weighting of slope angles, introducing rock-mass-failure susceptibilities inside rockfall source areas previously detected. Then rockfall runout assessment is performed using the GIS- and process-based software Flow-R, providing relative frequencies for runout. Thus, taking into consideration both susceptibility results, this approach can be used to establish, after calibration, hazard and risk maps at regional scale. As an example, a risk analysis of vehicle traffic exposed to rockfalls is performed along the main roads of the Swiss alpine valley of Bagnes.

Geoengineering Research for a Deep Underground Science and Engineering Laboratory in Sedimentary Rock

NASA Astrophysics Data System (ADS)

Mauldon, M.

2004-12-01

A process to identify world-class research for a Deep Underground Science and Engineering Laboratory (DUSEL) in the USA has been initiated by NSF. While allowing physicists to study, inter alia, dark matter and dark energy, this laboratory will create unprecedented opportunities for biologists to study deep life, geoscientists to study crustal processes and geoengineers to study the behavior of rock, fluids and underground cavities at depth, on time scales of decades. A substantial portion of the nation's future infrastructure is likely to be sited underground because of energy costs, urban crowding and vulnerability of critical surface facilities. Economic and safe development of subsurface space will require an improved ability to engineer the geologic environment. Because of the prevalence of sedimentary rock in the upper continental crust, much of this subterranean infrastructure will be hosted in sedimentary rock. Sedimentary rocks are fundamentally anisotropic due to lithology and bedding, and to discontinuities ranging from microcracks to faults. Fractures, faults and bedding planes create structural defects and hydraulic pathways over a wide range of scales. Through experimentation, observation and monitoring in a sedimentary rock DUSEL, in conjunction with high performance computational models and visualization tools, we will explore the mechanical and hydraulic characteristics of layered rock. DUSEL will permit long-term experiments on 100 m blocks of rock in situ, accessed via peripheral tunnels. Rock volumes will be loaded to failure and monitored for post-peak behavior. The response of large rock bodies to stress relief-driven, time-dependent strain will be monitored over decades. Large block experiments will be aimed at measurement of fluid flow and particle/colloid transport, in situ mining (incl. mining with microbes), remediation technologies, fracture enhancement for resource extraction and large scale long-term rock mass response to induced stresses - with parallel geophysical imaging of the rock mass (and subsequent verification) flow and transport processes, and time-dependent stress and strain. An experimental advantage of sedimentary rock is the presence of pervasive mechanical interfaces (bedding planes), which suggest a host of experimental designs on large rock blocks and slabs (induced flexure, shear strength of interfaces, etc). Thus DUSEL will enable fundamental research about the behavior of a layered rock mass - the dominant structural architecture in near-surface environments worldwide. A further benefit is the natural suitability of sedimentary rocks for experiments related to oil and gas production, or to CO2 sequestration. For example, fluid-induced fracturing of sedimentary rock has long been used by the hydrocarbon industry to improve oil and coal bed methane recovery. Since some fracturing agents are potential contaminants, a major concern and legal responsibility in the US is ensuring the integrity of nearby aquifers. Hydraulic fracturing from a sedimentary rock DUSEL will be followed by injection of low viscosity grout. The rock mass will then be mined back to expose network characteristics of the induced hydraulic fractures. Key questions related to hydrocarbon extraction, CO2 sequestration, waste isolation, and remediation of subsurface contaminants depend critically on the connectivity and architecture of fractures and on coupled thermal, hydrological, mechanical and chemical processes. Fluid flow, particle transport and reaction transport processes are coupled to the stress across fractures, and to thermal, chemical and hydraulic gradients. All can best be studied via large block tests in a subterranean laboratory, ideally in a sedimentary environment.

Improving DMS 9210 requirements for limestone rock asphalt - final report.

DOT National Transportation Integrated Search

2015-03-01

Limestone Rock Asphalt (LRA) mixtures have been produced and placed for several decades using : specification requirements currently listed under DMS 9210. Several districts have had placement issues : and premature failures at the beginning of 2010....

Study of Experiment on Rock-like Material Consist of fly-ash, Cement and Mortar

NASA Astrophysics Data System (ADS)

Nan, Qin; Hongwei, Wang; Yongyan, Wang

2018-03-01

Study the uniaxial compression test of rock-like material consist of coal ash, cement and mortar by changing the sand cement ratio, replace of fine coal, grain diameter, water-binder ratio and height-diameter ratio. We get the law of four factors above to rock-like material’s uniaxial compression characteristics and the quantitative relation. The effect law can be sum up as below: sample’s uniaxial compressive strength and elasticity modulus tend to decrease with the increase of sand cement ratio, replace of fine coal and water-binder ratio, and it satisfies with power function relation. With high ratio increases gradually, the uniaxial compressive strength and elastic modulus is lower, and presents the inverse function curve; Specimen tensile strength decreases gradually with the increase of fly ash. By contrast, uniaxial compression failure phenomenon is consistent with the real rock common failure pattern.

Thermal fatigue and thermal shock in bedrock: An attempt to unravel the geomorphic processes and products

NASA Astrophysics Data System (ADS)

Hall, Kevin; Thorn, Colin E.

2014-02-01

Widespread acceptance in science at-large notwithstanding, the ability of thermal stresses to produce thermal fatigue (TF) and/or thermal shock (TS) in bedrock and coarse debris in the field is often doubted. Commonly called insolation weathering in geomorphology, the results of questionable laboratory experiments have led many geomorphologists to consider terrestrial temperatures to be inadequate to generate thermally induced stresses leading to rock failure; the exceptions are the action of fire or lightning. We comprehensively survey the general scientific literature on TF and TS while rigorously scrutinizing that relating to geomorphology. Findings indicate theoretical and experimental information is adequate to establish the feasibility of TF and TS in rock stemming from rock temperatures monitored in the field. While TS may exhibit fracture patterns that are uniquely diagnostic, those of TF lack any such attributes. It would appear unlikely that TF can prepare or weaken rock to increase the likelihood of TS. The question of whether widespread polygonal versus rectilinear cracking is diagnostic of TS is presently an open one as possible explanations invoke process(es) and/or host material(s) and, consequently, to assign palaeoenvironmental significance to such fracture patterns is premature at this time. Further geomorphological laboratory research into TF and TS is merited as sufficient theoretical underpinning already exists. However, laboratory experimentation needs to be much more rigorously defined and executed and is faced with significant hurdles if it is to be effectively linked to field observations.

Qualitative evaluation of rock weir field performance and failure mechanisms

USGS Publications Warehouse

Mooney, David M.; Holmquist-Johnson, Christopher L.; Holburn, Elaina

2007-01-01

River spanning loose-rock structures provide sufficient head for irrigation diversion, permit fish passage over barriers, protect banks, stabilize degrading channels, activate side channels, reconnect floodplains, and create in-channel habitat. These structures are called by a variety of names including rock weirs, alphabet (U-, A-, V-, W-) weirs, Jhooks, and rock ramps. These structures share the common characteristics of:Loose rock construction materials (individually placed or dumped rocks with little or no concrete);Extents spanning the width of the river channel; andAn abrupt change in the water surface elevation at low flows.

Field evidence for control of quarrying by rock bridges in jointed bedrock

NASA Astrophysics Data System (ADS)

Hooyer, T. S.; Cohen, D. O.; Iverson, N. R.

2011-12-01

Quarrying is generally thought to be the most important mechanism by which glaciers erode bedrock. In quarrying models it is assumed that slow, subcritical, growth of pre-existing cracks rate-limits the process and occurs where there are large stress differences in the bed, such as near rock bumps where ice separates from the bed to form water-filled cavities. Owing to the direction of principal stresses in rocks associated with sliding and resultant cavity formation, models predict that quarrying will occur along cracks oriented perpendicular to the ice flow direction or parallel to zones of ice-bed contact. Preglacial cracks in rocks will tend to propagate mainly downward, and in sedimentary or some metamorphic rocks will merge with bedding planes, thereby helping to isolate rock blocks for dislodgement. In contrast to these model assumptions, new measurements of quarried surface orientations in the deglaciated forefield of nine glaciers in Switzerland and Canada indicate a strong correlation between orientations of pre-existing joints and quarried bedrock surfaces, independent of ice flow direction or ice-water contact lines. The strong correlation persists across all rock types, and rocks devoid of major joints lack quarried surfaces. We propose a new conceptual model of quarrying that idealizes the bedrock as a series of blocks separated by discontinuous preglacial joints containing intact rock bridges. Bridges concentrate stress differences caused by normal and shear forces acting at the rock surface. Failure of bridges is caused by slow subcritical crack growth enhanced by water pressure fluctuations. To lend credibility to this new model, we show field evidence of failed rock bridges in quarried surfaces and of rib marks on plumose structures that we interpret as arrest fracture fronts due to transient subglacial water-pressure fluctuations.

Geometrical and hydrogeological impact on the behaviour of deep-seated rock slides during reservoir impoundment

NASA Astrophysics Data System (ADS)

Lechner, Heidrun; Zangerl, Christian

2015-04-01

Given that there are still uncertainties regarding the deformation and failure mechanisms of deep-seated rock slides this study concentrates on key factors that influence the behaviour of rock slides in the surrounding of reservoirs. The focus is placed on the slope geometry, hydrogeology and kinematics. Based on numerous generic rock slide models the impacts of the (i) rock slide geometry, (ii) reservoir impoundment and level fluctuations, (iii) seepage and buoyancy forces and (iv) hydraulic conductivity of the rock slide mass and the basal shear zone are examined using limit equilibrium approaches. The geometry of many deep-seated rock slides in metamorphic rocks is often influenced by geological structures, e.g. fault zones, joints, foliation, bedding planes and others. With downslope displacement the rock slide undergoes a change in shape. Several observed rock slides in an advanced stage show a convex, bulge-like topography at the foot of the slope and a concave topography in the middle to upper part. Especially, the situation of the slope toe plays an important role for stability. A potentially critical situation can result from a partially submerged flat slope toe because the uplift due to water pressure destabilizes the rock slide. Furthermore, it is essential if the basal shear zone daylights at the foot of the slope or encounters alluvial or glacial deposits at the bottom of the valley, the latter having a buttressing effect. In this study generic rock slide models with a shear zone outcropping at the slope toe are established and systematically analysed using limit equilibrium calculations. Two different kinematic types are modelled: (i) a translational or planar and (ii) a rotational movement behaviour. Questions concerning the impact of buoyancy and pore pressure forces that develop during first time impoundment are of key interest. Given that an adverse effect on the rock slide stability is expected due to reservoir impoundment the extent of destabilisation is highly dependent on the ratio of the rock mass volume affected by buoyancy forces to the total volume of the rock slide. If a large rock mass volume ratio is submerged, huge buoyancy forces evolve and destabilize the slope significantly. Additionally, the influence of impoundment velocity on the rock slide behaviour and the impact of material properties of the rock masses are analysed. Reservoir water rapidly infiltrates into high-permeable rock slide masses evolving high pore pressures at the basal shear zone which leads to destabilisation. Conversely, reservoir water infiltrates slowly into low-permeable rock masses and the destabilizing effect of the pore water pressure might be compensated by a buttressing reservoir load over the low-permeable rock masses. Preliminary steady state calculations show that the factor of safety decreases constantly with increasing reservoir level until a certain threshold reservoir level and minimum factor of safety is reached. After exceeding this threshold level a further increase in reservoir impoundment leads to an increase of the factor of safety. This threshold reservoir level is reliant on the rock slide geometry and rock mass volume affected by buoyancy. Upcoming research is expected to provide new fundamentals for a comprehensive understanding of deformation and failure processes of deep-seated rock slides in order to perform reliable forecasts.

Monitoring and modeling ice-rock avalanches from ice-capped volcanoes: A case study of frequent large avalanches on Iliamna Volcano, Alaska

USGS Publications Warehouse

Huggel, C.; Caplan-Auerbach, J.; Waythomas, C.F.; Wessels, R.L.

2007-01-01

Iliamna is an andesitic stratovolcano of the Aleutian arc with regular gas and steam emissions and mantled by several large glaciers. Iliamna Volcano exhibits an unusual combination of frequent and large ice-rock avalanches in the order of 1 ?? 106??m3 to 3 ?? 107??m3 with recent return periods of 2-4??years. We have reconstructed an avalanche event record for the past 45??years that indicates Iliamna avalanches occur at higher frequency at a given magnitude than other mass failures in volcanic and alpine environments. Iliamna Volcano is thus an ideal site to study such mass failures and its relation to volcanic activity. In this study, we present different methods that fit into a concept of (1) long-term monitoring, (2) early warning, and (3) event documentation and analysis of ice-rock avalanches on ice-capped active volcanoes. Long-term monitoring methods include seismic signal analysis, and space-and airborne observations. Landsat and ASTER satellite data was used to study the extent of hydrothermally altered rocks and surface thermal anomalies at the summit region of Iliamna. Subpixel heat source calculation for the summit regions where avalanches initiate yielded temperatures of 307 to 613??K assuming heat source areas of 1000 to 25??m2, respectively, indicating strong convective heat flux processes. Such heat flow causes ice melting conditions and is thus likely to reduce the strength at the base of the glacier. We furthermore demonstrate typical seismic records of Iliamna avalanches with rarely observed precursory signals up to two hours prior to failure, and show how such signals could be used for a multi-stage avalanche warning system in the future. For event analysis and documentation, space- and airborne observations and seismic records in combination with SRTM and ASTER derived terrain data allowed us to reconstruct avalanche dynamics and to identify remarkably similar failure and propagation mechanisms of Iliamna avalanches for the past 45??years. Simple avalanche flow modeling was able to reasonably replicate Iliamna avalanches and can thus be applied for hazard assessments. Hazards at Iliamna Volcano are low due to its remote location; however, we emphasize the transfer potential of the methods presented here to other ice-capped volcanoes with much higher hazards such as those in the Cascades or the Andes. ?? 2007 Elsevier B.V. All rights reserved.

Experimental study on the confinement-dependent characteristics of a Utah coal considering the anisotropy by cleats

PubMed Central

Kim, Bo-Hyun; Walton, Gabriel; Larson, Mark K.; Berry, Steve

2018-01-01

Characterizing a coal from an engineering perspective for design of mining excavations is critical in order to prevent fatalities, as underground coal mines are often developed in highly stressed ground conditions. Coal pillar bursts involve the sudden expulsion of coal and rock into the mine opening. These events occur when relatively high stresses in a coal pillar, left for support in underground workings, exceed the pillar’s load capacity causing the pillar to rupture without warning. This process may be influenced by cleating, which is a type of joint system that can be found in coal rock masses. As such, it is important to consider the anisotropy of coal mechanical behavior. Additionally, if coal is expected to fail in a brittle manner, then behavior changes, such as the transition from extensional to shear failure, have to be considered and reflected in the adopted failure criteria. It must be anticipated that a different failure mechanism occurs as the confinement level increases and conditions for tensile failure are prevented or strongly diminished. The anisotropy and confinement dependency of coal behavior previously mentioned merit extensive investigation. In this study, a total of 84 samples obtained from a Utah coal mine were investigated by conducting both unconfined and triaxial compressive tests. The results showed that the confining pressure dictated not only the peak compressive strength but also the brittleness as a function of the major to the minor principal stress ratio. Additionally, an s-shaped brittle failure criterion was fitted to the results, showing the development of confinement-dependent strength. Moreover, these mechanical characteristics were found to be strongly anisotropic, which was associated with the orientation of the cleats relative to the loading direction. PMID:29780272

Rock fracture processes in chemically reactive environments

NASA Astrophysics Data System (ADS)

Eichhubl, P.

2015-12-01

Rock fracture is traditionally viewed as a brittle process involving damage nucleation and growth in a zone ahead of a larger fracture, resulting in fracture propagation once a threshold loading stress is exceeded. It is now increasingly recognized that coupled chemical-mechanical processes influence fracture growth in wide range of subsurface conditions that include igneous, metamorphic, and geothermal systems, and diagenetically reactive sedimentary systems with possible applications to hydrocarbon extraction and CO2 sequestration. Fracture processes aided or driven by chemical change can affect the onset of fracture, fracture shape and branching characteristics, and fracture network geometry, thus influencing mechanical strength and flow properties of rock systems. We are investigating two fundamental modes of chemical-mechanical interactions associated with fracture growth: 1. Fracture propagation may be aided by chemical dissolution or hydration reactions at the fracture tip allowing fracture propagation under subcritical stress loading conditions. We are evaluating effects of environmental conditions on critical (fracture toughness KIc) and subcritical (subcritical index) fracture properties using double torsion fracture mechanics tests on shale and sandstone. Depending on rock composition, the presence of reactive aqueous fluids can increase or decrease KIc and/or subcritical index. 2. Fracture may be concurrent with distributed dissolution-precipitation reactions in the hostrock beyond the immediate vicinity of the fracture tip. Reconstructing the fracture opening history recorded in crack-seal fracture cement of deeply buried sandstone we find that fracture length growth and fracture opening can be decoupled, with a phase of initial length growth followed by a phase of dominant fracture opening. This suggests that mechanical crack-tip failure processes, possibly aided by chemical crack-tip weakening, and distributed solution-precipitation creep in the hostrock can independently affect fracture opening displacement and thus fracture aperture profiles and aperture distribution.

Field-scale and wellbore modeling of compaction-induced casing failures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hilbert, L.B. Jr.; Gwinn, R.L.; Moroney, T.A.

1999-06-01

Presented in this paper are the results and verification of field- and wellbore-scale large deformation, elasto-plastic, geomechanical finite element models of reservoir compaction and associated casing damage. The models were developed as part of a multidisciplinary team project to reduce the number of costly well failures in the diatomite reservoir of the South Belridge Field near Bakersfield, California. Reservoir compaction of high porosity diatomite rock induces localized shearing deformations on horizontal weak-rock layers and geologic unconformities. The localized shearing deformations result in casing damage or failure. Two-dimensional, field-scale finite element models were used to develop relationships between field operations, surfacemore » subsidence, and shear-induced casing damage. Pore pressures were computed for eighteen years of simulated production and water injection, using a three-dimensional reservoir simulator. The pore pressures were input to the two-dimensional geomechanical field-scale model. Frictional contact surfaces were used to model localized shear deformations. To capture the complex casing-cement-rock interaction that governs casing damage and failure, three-dimensional models of a wellbore were constructed, including a frictional sliding surface to model localized shear deformation. Calculations were compared to field data for verification of the models.« less

Well bore breakouts and in situ stress

USGS Publications Warehouse

Zoback, Mark D.; Moos, Daniel; Mastin, Larry; Anderson, Roger N.

1985-01-01

The detailed cross-sectional shape of stress induced well bore breakouts has been studied using specially processed ultrasonic borehole televiewer data. Breakout shapes are shown for a variety of rock types and introduce a simple elastic failure model which explains many features of the observations. Both the observations and calculations indicate that the breakouts define relatively broad and flat curvilinear surfaces which enlarge the borehole in the direction of minimum horizontal compression. Refs.

A Discrete Element Method Approach to Progressive Localization of Damage in Granular Rocks and Associated Seismicity

NASA Astrophysics Data System (ADS)

Vora, H.; Morgan, J.

2017-12-01

Brittle failure in rock under confined biaxial conditions is accompanied by release of seismic energy, known as acoustic emissions (AE). The objective our study is to understand the influence of elastic properties of rock and its stress state on deformation patterns, and associated seismicity in granular rocks. Discrete Element Modeling is used to simulate biaxial tests on granular rocks of defined grain size distribution. Acoustic Energy and seismic moments are calculated from microfracture events as rock is taken to conditions of failure under different confining pressure states. Dimensionless parameters such as seismic b-value and fractal parameter for deformation, D-value, are used to quantify seismic character and distribution of damage in rock. Initial results suggest that confining pressure has the largest control on distribution of induced microfracturing, while fracture energy and seismic magnitudes are highly sensitive to elastic properties of rock. At low confining pressures, localized deformation (low D-values) and high seismic b-values are observed. Deformation at high confining pressures is distributed in nature (high D-values) and exhibit low seismic b-values as shearing becomes the dominant mode of microfracturing. Seismic b-values and fractal D-values obtained from microfracturing exhibit a linear inverse relationship, similar to trends observed in earthquakes. Mode of microfracturing in our simulations of biaxial compression tests show mechanistic similarities to propagation of fractures and faults in nature.

Improving DMS 9210 requirements for limestone rock asphalt : year one interim report.

DOT National Transportation Integrated Search

2013-05-01

Limestone Rock Asphalt (LRA) mixtures have been produced and placed for several decades using specification requirements currently listed under DMS 9210. Several Districts have had placement issues and premature failures at the beginning of 2010. The...

Impaired cytoskeletal arrangements and failure of ventral body wall closure in chick embryos treated with rock inhibitor (Y-27632).

PubMed

Duess, Johannes W; Puri, Prem; Thompson, Jennifer

2016-01-01

Rho-associated kinase (ROCK) signaling regulates numerous fundamental developmental processes during embryogenesis, primarily by controlling actin-cytoskeleton assembly and cell contractility. ROCK knockout mice exhibit a ventral body wall defect (VBWD) phenotype due to disorganization of actin filaments at the umbilical ring. However, the exact molecular mechanisms leading to VBWD still remain unclear. Improper somitogenesis has been hypothesized to contribute to failure of VBW closure. We designed this study to investigate the hypothesis that administration of ROCK inhibitor (Y-27632) disrupts cytoskeletal arrangements in morphology during early chick embryogenesis, which may contribute to the development of VBWD. At 60 h incubation, chick embryos were explanted into shell-less culture and treated with 50 µL of vehicle for controls (n = 33) or 50 µL of 500 µM of Y-27632 for the experimental group (Y-27, n = 56). At 8 h post-treatment, RT-PCR was performed to evaluate mRNA levels of N-cadherin, E-cadherin and connexin43. Immunofluorescence confocal microscopy was performed to analyze the expression and distribution of actin, vinculin and microtubules in the neural tube and somites. A further cohort of embryos was treated in ovo by dropping 50 µL of vehicle or 50 µL of different concentrations of Y-27632 onto the embryo and allowing development to 12 and 14 days for further assessment. Gene expression levels of N-cadherin, E-cadherin and connexin43 were significantly decreased in treated embryos compared with controls (p < 0.05). Thickened actin filament bundles were recorded in the neural tube of Y-27 embryos. In somites, cells were dissociated with reduced actin distribution in affected embryos. Clumping of vinculin expression was found in the neural tube and somites, whereas reduced expression of microtubules was observed in Y-27 embryos compared with controls. At 12 and 14 days of development, affected embryos presented with an enlarged umbilical ring and herniation of abdominal contents through the defect. ROCK inhibition alters cytoskeletal arrangement during early chick embryogenesis, which may contribute to failure of anterior body wall closure causing VBWD at later stages of development.

Studying physical properties of deformed intact and fractured rocks by micro-scale hydro-mechanical-seismicity model

NASA Astrophysics Data System (ADS)

Raziperchikolaee, Samin

The pore pressure variation in an underground formation during hydraulic stimulation of low permeability formations or CO2 sequestration into saline aquifers can induce microseismicity due to fracture generation or pre-existing fracture activation. While the analysis of microseismic data mainly focuses on mapping the location of fractures, the seismic waves generated by the microseismic events also contain information for understanding of fracture mechanisms based on microseismic source analysis. We developed a micro-scale geomechanics, fluid-flow and seismic model that can predict transport and seismic source behavior during rock failure. This model features the incorporation of microseismic source analysis in fractured and intact rock transport properties during possible rock damage and failure. The modeling method considers comprehensive grains and cements interaction through a bonded-particle-model. As a result of grain deformation and microcrack development in the rock sample, forces and displacements in the grains involved in the bond breakage are measured to determine seismic moment tensor. In addition, geometric description of the complex pore structure is regenerated to predict fluid flow behavior of fractured samples. Numerical experiments are conducted for different intact and fractured digital rock samples, representing various mechanical behaviors of rocks and fracture surface properties, to consider their roles on seismic and transport properties of rocks during deformation. Studying rock deformation in detail provides an opportunity to understand the relationship between source mechanism of microseismic events and transport properties of damaged rocks to have a better characterizing of fluid flow behavior in subsurface formations.

The role of post-failure brittleness of soft rocks in the assessment of stability of intact masses: FDEM technique applications to ideal problems

NASA Astrophysics Data System (ADS)

Lollino, Piernicola; Andriani, Gioacchino Francesco; Fazio, Nunzio Luciano; Perrotti, Michele

2016-04-01

Strain-softening under low confinement stress, i.e. the drop of strength that occurs in the post-failure stage, represents a key factor of the stress-strain behavior of rocks. However, this feature of the rock behavior is generally underestimated or even neglected in the assessment of boundary value problems of intact soft rock masses. This is typically the case when the stability of intact rock masses is treated by means of limit equilibrium or finite element analyses, for which rigid-plastic or elastic perfectly-plastic constitutive models, generally implementing peak strength conditions of the rock, are respectively used. In fact, the aforementioned numerical techniques are characterized by intrinsic limitations that do not allow to account for material brittleness, either for the method assumptions or due to numerical stability problems, as for the case of the finite element method, unless sophisticated regularization techniques are implemented. However, for those problems that concern the stability of intact soft rock masses at low stress levels, as for example the stability of shallow underground caves or that of rock slopes, the brittle stress-strain response of rock in the post-failure stage cannot be disregarded due to the risk of overestimation of the stability factor. This work is aimed at highlighting the role of post-peak brittleness of soft rocks in the analysis of specific ideal problems by means of the use of a hybrid finite-discrete element technique (FDEM) that allows for the simulation of the rock stress-strain brittle behavior in a proper way. In particular, the stability of two ideal cases, represented by a shallow underground rectangular cave and a vertical cliff, has been analyzed by implementing a post-peak brittle behavior of the rock and the comparison with a non-brittle response of the rock mass is also explored. To this purpose, the mechanical behavior of a soft calcarenite belonging to the Calcarenite di Gravina formation, extensively outcropping in Puglia (Southern Italy), and the corresponding features of the post-peak behavior as measured in the laboratory, have been used as a reference in this work, as well as the typical geometrical features of underground cavities and rock cliffs, as observed in Southern Italy, have been adopted for the simulations. The numerical results indicate the strong impact for the assessment of stability when rock post-peak brittleness is accounted for, if compared with perfectly plastic assumptions, and the need for adopting numerical techniques, as the FDEM approach, to take properly into account this important aspect of the rock behavior is highlighted.

Experimental Investigation of the Influence of Confining Stress on Hard Rock Fragmentation Using a Conical Pick

NASA Astrophysics Data System (ADS)

Li, Xibing; Wang, Shaofeng; Wang, Shanyong

2018-01-01

High geostress is a prominent condition in deep excavations and affects the cuttability of deep hard rock. This study aims to determine the influence of confining stress on hard rock fragmentation as applied by a conical pick. Using a true triaxial test apparatus, static and coupled static and dynamic loadings from pick forces were applied to end faces of cubic rock specimens to break them under biaxial, uniaxial and stress-free confining stress conditions. The cuttability indices (peak pick force, insertion depth and disturbance duration), failure patterns and fragment sizes were measured and compared to estimate the effects of confining stress. The results show that the rock cuttabilities decreased in order from rock breakages under stress-free conditions to uniaxial confining stress and then to biaxial confining stress. Under biaxial confining stress, only flake-shaped fragments were stripped from the rock surfaces under the requirements of large pick forces or disturbance durations. As the level of uniaxial confining stress increased, the peak pick force and the insertion depth initially increased and then decreased, and the failure patterns varied from splitting to partial splitting and then to rock bursts with decreasing average fragment sizes. Rock bursts will occur under elastic compression via ultra-high uniaxial confining stresses. There are two critical uniaxial confining stress levels, namely stress values at which peak pick forces begin to decrease and improve rock cuttability, and those at which rock bursts initially occur and cutting safety decreases. In particular, hard rock is easiest to split safely and efficiently under stress-free conditions. Moreover, coupled static preloading and dynamic disturbance can increase the efficiency of rock fragmentation with increasing preloading levels and disturbance amplitudes. The concluding remarks confirm hard rock cuttability using conical pick, which can improve the applicability of mechanical excavation in deep hard rock masses.

Failure Forecasting in Triaxially Stressed Sandstones

NASA Astrophysics Data System (ADS)

Crippen, A.; Bell, A. F.; Curtis, A.; Main, I. G.

2017-12-01

Precursory signals to fracturing events have been observed to follow power-law accelerations in spatial, temporal, and size distributions leading up to catastrophic failure. In previous studies this behavior was modeled using Voight's relation of a geophysical precursor in order to perform `hindcasts' by solving for failure onset time. However, performing this analysis in retrospect creates a bias, as we know an event happened, when it happened, and we can search data for precursors accordingly. We aim to remove this retrospective bias, thereby allowing us to make failure forecasts in real-time in a rock deformation laboratory. We triaxially compressed water-saturated 100 mm sandstone cores (Pc= 25MPa, Pp = 5MPa, σ = 1.0E-5 s-1) to the point of failure while monitoring strain rate, differential stress, AEs, and continuous waveform data. Here we compare the current `hindcast` methods on synthetic and our real laboratory data. We then apply these techniques to increasing fractions of the data sets to observe the evolution of the failure forecast time with precursory data. We discuss these results as well as our plan to mitigate false positives and minimize errors for real-time application. Real-time failure forecasting could revolutionize the field of hazard mitigation of brittle failure processes by allowing non-invasive monitoring of civil structures, volcanoes, and possibly fault zones.

Impact of ductility on hydraulic fracturing in shales

NASA Astrophysics Data System (ADS)

MacMinn, Chris; Auton, Lucy

2016-04-01

Hydraulic fracturing is a method for extracting natural gas and oil from low-permeability rocks such as shale via the high-pressure injection of fluid into the bulk of the rock. The goal is to initiate and propagate fractures that will provide hydraulic access deeper into the reservoir, enabling gas or oil to be collected from a larger region of the rock. Fracture is the tensile failure of a brittle material upon reaching a threshold tensile stress, but some shales have a high clay content and may yield plastically before fracturing. Plastic deformation is the shear failure of a ductile material, during which stress relaxes through irreversible rearrangements of the particles of the material. Here, we investigate the impact of the ductility of shales on hydraulic fracturing. We first consider a simple, axisymmetric model for radially outward fluid injection from a wellbore into a ductile porous rock. We use this model to show that plastic deformation greatly reduces the maximum tensile stress, and that this maximum stress does not always occur at the wellbore. We then complement these results with laboratory experiments in an analogue system, and with numerical simulations based on the discrete element method (DEM), both of which suggest that ductile failure can indeed dramatically change the resulting deformation pattern. These results imply that hydraulic fracturing may fail in ductile rocks, or that the required injection rate for fracking may be much larger than the rate predicted from models that assume purely elastic mechanical behavior.

Effect of σ2 on All Aspects of Failure in Rocks from Granite to Sandstone

NASA Astrophysics Data System (ADS)

Haimson, B. C.; Ma, X.

2014-12-01

We have studied the effect of σ2 on failure characteristics of two crystalline and three clastic rocks subjected to true triaxial stresses. Common to all rocks tested is the rise in both strain localization onset and σ1 at failure (σ1,peak) for a given σ3, as σ2 is elevated beyond its base level (σ2 = σ3). σ1,peak reaches a maximum at some level of σ2, beyond which it gradually declines, approaching its base magnitude when σ2 nears its own maximum. Failure-plane angle with respect to σ1 for a given σ3 also increases with σ2, at least until the maximum σ1,peak is reached. Westerly granite (Haimson and Chang, IJRMMS, 2000) and KTB amphibolite (Chang and Haimson, JGR, 2000), exhibited a dramatic σ2 effect: at low σ3 (20-30 MPa), higher σ2 lifted σ1,peak by up to 50% over its base level. At high σ3, the increase in σ1,peak was reduced, but even at σ3 = 100 MPa, maximum σ1,peak in both rocks was over 20% higher than its base level. Failure mode remained brittle throughout the stress range tested, but the onset of dilatancy rose with σ2, as did the failure-plane (shear-band) angle (by up to 20°). A gentler effect of σ2 on σ1, peak and failure-plane angle was observed in the clastics, and that effect subsided as porosity increased. In low porosity (φ = 7%) TCDP siltstone (Oku, et al, GRL, 2007), the maximum σ1,peak at σ3 = 25 MPa was about 30% larger than at σ2 = σ3 level, and only 12.5% larger at σ3 = 100 MPa. Failure mode stayed brittle throughout, but shear-band angle increase with σ2 was limited to about 10°, irrespective of σ3 level. An even smaller σ2 effect was observed in Coconino sandstone (φ = 17%) (Ma, PhD thesis, 2014). σ1,peak reached a maximum of about 10% higher than at σ2 = σ3 level; failure-plane angle rise with σ2 was less than 10°. The weakest σ2 effect was found in the high porosity (φ= 25%) Bentheim sandstone (Ma, PhD thesis, 2014). Here σ1, peak reached a maximum of well under 10% higher than its base magnitude, regardless of σ3 level; average failure-plane angle rise with σ2 was below 10°. Failure at σ3 = 150 MPa was along a compaction band(s) normal to σ1, regardless of σ2. Both Coconino and Bentheim underwent dilatant failure at low σ3, shifting to compactive failure at high σ3 levels. But σ2 also affected the failure mode: compactive failure at σ2 = σ3 gradually reverted to a dilatant mode as σ2 was raised.

Meteoritic basalts. Final report, 1986-1989

DOE Office of Scientific and Technical Information (OSTI.GOV)

Treiman, A.H.

1989-10-01

The objectives were to: explain the abundances of siderophile elements in the SNC meteorite suite, of putative Martian origin; discover the magmatic origins and possibly magma compositions behind the Nakhla meteorite, one of the SNC meteorites; and a re-evaluation of the petrology of Angra dos Reis, a unique meteorite linked to the earliest planetary bodies of the solar nebula. A re-evaluation of its petrography showed that the accepted scenario for its origin, as a cumulate igneous rock, was not consistent with the meteorite's textures (Treiman). More likely is that the meteorite represents a prophyritic igneous rock, originally with magma dominant.more » Studies of the Nakhla meteorite, of possible Martian origin, although difficult, were successful. It became necessary to reject the basic categorization of Nakhla: that is was a cumulate igneous rock. Detailed studies of the chemical zoning of Nakhlas' minerals, coupled with the failure of experimental studies to yield expected results, forced the conclusion that Nakhla is not a cumulate rock in the usual sense: a rock composed of igneous crystals and intercrystal magma. Study of the siderophile element abundances in the SNC meteorite groups involved trying to find reasonable core formation processes and parameters that would reproduce the observed abundances. Modelling was successful, and delimited a range of models which overlap with those reasonable from geophysical constraints.« less

Meteoritic basalts

NASA Technical Reports Server (NTRS)

Treiman, Allan H.

1989-01-01

The objectives were to: explain the abundances of siderophile elements in the SNC meteorite suite, of putative Martian origin; discover the magmatic origins and possibly magma compositions behind the Nakhla meteorite, one of the SNC meteorites; and a re-evaluation of the petrology of Angra dos Reis, a unique meteorite linked to the earliest planetary bodies of the solar nebula. A re-evaluation of its petrography showed that the accepted scenario for its origin, as a cumulate igneous rock, was not consistent with the meteorite's textures (Treiman). More likely is that the meteorite represents a prophyritic igneous rock, originally with magma dominant. Studies of the Nakhla meteorite, of possible Martian origin, although difficult, were successful. It became necessary to reject the basic categorization of Nakhla: that is was a cumulate igneous rock. Detailed studies of the chemical zoning of Nakhlas' minerals, coupled with the failure of experimental studies to yield expected results, forced the conclusion that Nakhla is not a cumulate rock in the usual sense: a rock composed of igneous crystals and intercrystal magma. Study of the siderophile element abundances in the SNC meteorite groups involved trying to find reasonable core formation processes and parameters that would reproduce the observed abundances. Modelling was successful, and delimited a range of models which overlap with those reasonable from geophysical constraints.

Subsurface Evolution: Weathering and Mechanical Strength Reduction in Bedrock of Lower Gordon Gulch, Colorado Front Range

NASA Astrophysics Data System (ADS)

Kelly, P. J.; Anderson, S. P.; Anderson, R. S.; Blum, A.; Foster, M. A.; Langston, A. L.

2011-12-01

Weathering processes drive mobile regolith production at the surface of the earth. Chemical and physical weathering weakens rock by creating porosity, opening fractures, and transforming minerals. Increased porosity provides habitat for living organisms, which aid in further breakdown of the rock, leaving it more susceptible to displacement and transport. In this study, we test mechanical and chemical characteristics of weathered profiles to better understand weathering processes. We collect shallow bedrock cores from tors and isovolumetrically weathered bedrock in lower Gordon Gulch to characterize the mechanical strength, mineralogy, and bulk chemistry of samples to track changes in the subsurface as bedrock weathers to mobile regolith. Gordon Gulch is a small (2.7 km2), E-W trending catchment within the Boulder Creek Critical Zone Observatory underlain by Pre-Cambrian gneiss and granitic bedrock. The basin is typical of the "Rocky Mountain Surface" of the Front Range, characterized by low relief, a lack of glacial or fluvial incision, and deep weathering. Although the low-curvature, low-relief Rocky Mountain Surface would appear to indicate a landscape roughly in steady-state, shallow seismic surveys (Befus et al., 2011, Vadose Zone Journal) indicate depth to bedrock is highly variable. Block style release of saprolite into mobile regolith could explain this high variability and should be observable in geotechnical testing. Gordon Gulch also displays a systematic slope-aspect dependent control on weathering, with N-facing hillslopes exhibiting deeper weathering profiles than the S-facing hillslope. We believe comparisons of paired geotechnical-testing, XRD, and XRF analyses may explain this hillslope anisotropy. Rock quality designation (RQD) values, a commonly used indicator of rock mass quality (ASTM D6032), from both N- and S- facing aspects in Gordon Gulch indicate that granitic bedrock in both outcrop and saprolitic rock masses is poor to very poor. Brazilian tensile testing of outcrop core samples show relatively low tensile failure forces, and exhibit a roughly logarithmic increase in failure force, and hence tensile strength, with depth. For many of the granitic strength profiles, the point of greatest curvature is around 0.5 m depth. Tests reveal small-scale variation in the tensile strength, suggesting that the tight fracture-spacing bounding blocks of saprolite plays an important role in regolith production. The origin of the micro- and macro-fractures is unclear. Preliminary results do not correlate clear depth-trends in mineralogy or bulk chemistry with mechanical strength. The lack of a strong signature from chemical or mineralogical weathering suggests that mechanical processes, such as frost cracking or biotite hydration, may dominate.

Numerical modelling of the formation of fibrous bedding-parallel veins

NASA Astrophysics Data System (ADS)

Torremans, Koen; Muchez, Philippe; Sintubin, Manuel

2014-05-01

Bedding-parallel veins with a fibrous infill oriented orthogonal to the vein wall, are often observed in fine-grained metasedimentary sequences. Several mechanisms have been proposed for their formation, mostly with respect to effects of fluid overpressures and anisotropy of the host-rock fabric in order to explain the inferred extensional failure with sub-vertical opening. Abundant pre-folding, bedding-parallel fibrous dolomite veins are found associated with the Nkana-Mindola stratiform Cu-Co deposit in Zambia. The goal of this study is to better understand the formation mechanisms of these veins and to explain their particular spatial and thickness distribution, with respect to failure of transversely isotropic rocks. The spatial distribution and thickness variation of these veins was quantified during a field campaign in thirteen line transects perpendicular to undeformed veins in underground crosscuts. The fibrous dolomite veins studied are not related to lithological contrasts, but to a strong bedding-parallel shaly fabric, typical for the black shale facies of the Copperbelt Orebody Member. The host rock can hence be considered as transversely isotropic. Growth morphologies vary from antitaxial with a pronounced median surface to asymmetric syntaxial, always with small but quantifiable growth competition. A microstructural fabric study reveals that the undeformed dolomite veins show low-tortuosity vein walls and quantifiable growth competition. Here, we use a Discrete Element Method numerical modelling approach with ESyS-Particle (http://launchpad.net/esys-particle) to simulate the observed properties of the veins. Calibrated numerical specimens with a transversely isotropic matrix are repeatedly brought to failure under constant strain rates by changing the effective strain rates at model boundaries. After each fracture event, fractures in the numerical model are filled with cohesive vein material and the experiment is repeated. By systematically varying stress states, fluid pressures and mechanical properties of materials (host rock, vein infill and interface), we attempt to reproduce the characteristics of spatial distribution and thickness variation of the veins. Four parameter sets of mechanical micro-properties are defined in the models, essentially yielding (1) a competent and (2) incompetent matrix, (3) a vein material and (4) a vein-matrix interface. Each combination of parameters and particle packings is calibrated to fit a predetermined Mohr-Coulomb type failure envelope, via an automated calibration procedure. Preliminary tests already show that by varying these parameters, we are able to simulate realistically distributed cracking through crack-seal processes. Different types of veins and vein generations can be modelled, ranging from single veins, over crack-seal veins to anastomosing veins, by varying the mechanical strength of competent and incompetent matrix, vein and interface material. Further results of this approach will be presented. We will discuss our results with respect to mechanisms proposed in the literature for bedding-parallel, fibrous veins in metasedimentary rock sequences.

Relating rock avalanche morphology to emplacement processes

NASA Astrophysics Data System (ADS)

Dufresne, Anja; Prager, Christoph; Bösmeier, Annette

2015-04-01

The morphology, structure and sedimentological characteristics of rock avalanche deposits reflect both internal emplacement processes and external influences, such as runout path characteristics. The latter is mainly predisposed by topography, substrate types, and hydrogeological conditions. Additionally, the geological setting at the source slope controls, e.g. the spatial distribution of accumulated lithologies and hence material property-related changes in morphology, or the maximum clast size and amount of fines of different lithological units. The Holocene Tschirgant rock avalanche (Tyrol, Austria) resulted from failure of an intensely deformed carbonate rock mass on the southeast face of a 2,370-m-high mountain ridge. The initially sliding rock mass rapidly fragmented as it moved towards the floor of the Inn River valley. Part of the 200-250 x 106 m3 (Patzelt 2012) rock avalanche debris collided with and moved around an opposing bedrock ridge and flowed into the Ötz valley, reaching up to 6.3 km from source. Where the Tschirgant rock avalanche spread freely it formed longitudinal ridges aligned along motion direction as well as smaller hummocks. Encountering high topography, it left runup ridges, fallback patterns (i.e. secondary collapse), and compressional morphology (successively elevated, transverse ridges). Further evidence for the mechanical landslide behaviour is given by large volumes of mobilized valley-fill sediments (polymict gravels and sands). These sediments indicate both shearing and compressional faulting within the rock avalanche mass (forming their own morphological units through, e.g. in situ bulldozing or as distinctly different hummocky terrain), but also indicate extension of the spreading landslide mass (i.e. intercalated/injected gravels encountered mainly in morphological depressions between hummocks). Further influences on its morphology are given by the different lithological units. E.g. the transition from massive dolomite/limestone sequences to weaker siliciclastic and evaporitic beds (sand-/siltstones, rauhwacken) can be pinpointed on LiDAR shaded relief images of the rock avalanche deposit. Hence, several morphological signatures are clearly related to differences in mechanical behaviour of the involved lithologies, whereas others reflect particular emplacement modes of the same rock unit: e.g. rockslide motion versus rock avalanche spreading. Reference Patzelt G. 2012. The rock avalanches of Tschirgant and Haiming (Upper Inn Valley, Tyrol, Austria), comment on the map supply. (German language only). Jahrbuch der Geologischen Bundesanstalt 152(1-4): 13-24.

Long-Term Effect of Fault-Controlled CO2 Alteration on the Weakening and Strengthening of Reservoir and Seal Lithologies at Crystal Geyser, Green River, Utah

NASA Astrophysics Data System (ADS)

Major, J. R.; Eichhubl, P.; Dewers, T. A.

2014-12-01

An understanding of the coupled chemical and mechanical properties and behavior of reservoir and seal rocks is critical for assessing both the short and long term security of sequestered CO2. A combined structural diagenesis approach using observations from natural analogs has great advantages for understanding these properties over longer time scales than is possible using laboratory or numerical experiments. Current numerical models evaluating failure of reservoirs and seals during and after CO2 injection in the subsurface are just beginning to account for such coupled processes. Well-characterized field studies of natural analogs such as Crystal Geyser, Utah, are essential for providing realistic input parameters, calibration, and testing of numerical models across a range of spatial and temporal scales. Fracture mechanics testing was performed on a suite of naturally altered and unaltered reservoir and seal rocks exposed at the Crystal Geyser field site. These samples represent end-products of CO2-related alteration over geologic (>103 yr) time scales. Both the double torsion and short rod test methods yield comparable results on the same samples. Tests demonstrate that CO2-related alteration has weakened one reservoir sandstone lithology by approximately 50%, but the subcritical index is not significantly affected. An altered siltstone sample also shows a reduction in fracture toughness values and lowered subcritical index in comparison to unaltered siltstone. In contrast, elevated calcite content in shales due to CO2 alteration has increased fracture toughness. Similarly, fracture toughness was increased in what is otherwise a weak, poorly cemented sandstone unit due to increased calcite cement. Combined, these results demonstrate that CO2-related alteration generally weakens rock to fracturing (i.e. lowers fracture toughness), except in cases where calcite cementation is significantly increased. The natural system at Crystal Geyser demonstrates that water-CO2-rock interaction driven by changes in the geochemical environment have measurably altered rock geomechanical properties and that some rock units may become more prone to failure, ultimately leading to fracturing and leakage of subsurface reservoirs. These results also have application for CO2-based enhanced oil recovery.

Asymmetric deformation structure of lava spine in Unzen Volcano, Japan

NASA Astrophysics Data System (ADS)

Miwa, T.; Okumura, S.; Matsushima, T.; Shimizu, H.

2013-12-01

Lava spine is commonly generated by effusive eruption of crystal-rich, dacitic-andesitic magmas. Especially, deformation rock on surface of lava spine has been related with processes of magma ascent, outgassing, and generation of volcanic earthquake (e.g., Cashman et al. 2008). To reveal the relationships and generation process of the spine, it is needed to understand a spatial distribution of the deformation rock. Here we show the spatial distribution of the deformation rock of lava spine in the Unzen volcano, Japan, to discuss the generation process of the spine. The lava spine in Unzen volcano is elongated in the E-W direction, showing a crest like shape with 150 long, 40 m wide and 50 m high. The lava spine is divided into following four parts: 1) Massive dacite part: Dense dacite with 30 m of maximum thickness, showing slickenside on the southern face; 2) Sheared dacite part: Flow band developed dacite with 1.0 m of maximum thickness; 3) Tuffisite part: Network of red colored vein develops in dacite with 0.5 m of maximum thickness; 4) Breccia part: Dacitic breccia with 10 m of maximum thickness. The Breccia part dominates in the northern part of the spine, and flops over Massive dacite part accross the Sheared dacite and Tuffisite parts. The slickenside on southern face of massive dacite demonstrates contact of solids. The slickenside breaks both of phenocryst and groundmass, demonstrating that the slickenside is formed after significant crystallization at the shallow conduit or on the ground surface. The lineation of the slickenside shows E-W direction with almost horizontal rake angle, which is consistent with the movement of the spine to an east before emplacement. Development of sub-vertical striation due to extrusion was observed on northern face of the spine (Hayashi, 1994). Therefore, we suggest that the spine just at extrusion consisted of Massive dacite, Sheared dacite, Tuffisite, Breccia, and Striation parts in the northern half of the spine. Such a variation of rock type is analogous to tectonic fault zone, suggesting that brittle failure of rigid magma due to contact with the conduit wall. Also similar variation is observed in the spine of Mt. St. Helens (Kendrick et al., 2012), which implies the existence of fault zone and brittle failure of magma are common features in the lava spine. The lava spine in Unzen volcano exhibits asymmetric deformation structure about direction of north and south. There is positive correlation between width and length in tectonic fault (Wells and Coppersmith, 1994). Therefore, development of fault zone (Sheared dacite, Tuffisite, and Breccia parts) in northern half may indicate that brittle failure starts at the deeper conduit for the northern half than the southern half of the spine. The asymmetry of magma ascent process is possible to result in asymmetries of outgassing path and location of volcanic earthquake in the conduit.

Numerical Model for the Study of the Strength and Failure Modes of Rock Containing Non-Persistent Joints

NASA Astrophysics Data System (ADS)

Vergara, Maximiliano R.; Van Sint Jan, Michel; Lorig, Loren

2016-04-01

The mechanical behavior of rock containing parallel non-persistent joint sets was studied using a numerical model. The numerical analysis was performed using the discrete element software UDEC. The use of fictitious joints allowed the inclusion of non-persistent joints in the model domain and simulating the progressive failure due to propagation of existing fractures. The material and joint mechanical parameters used in the model were obtained from experimental results. The results of the numerical model showed good agreement with the strength and failure modes observed in the laboratory. The results showed the large anisotropy in the strength resulting from variation of the joint orientation. Lower strength of the specimens was caused by the coalescence of fractures belonging to parallel joint sets. A correlation was found between geometrical parameters of the joint sets and the contribution of the joint sets strength in the global strength of the specimen. The results suggest that for the same dip angle with respect to the principal stresses; the uniaxial strength depends primarily on the joint spacing and the angle between joints tips and less on the length of the rock bridges (persistency). A relation between joint geometrical parameters was found from which the resulting failure mode can be predicted.

The major mass movements of the Western Dolomites (Italy)

NASA Astrophysics Data System (ADS)

Ostermann, Marc; Gruber, Alfred

2014-05-01

Major gravitational slope deformations are widely disseminated in the Dolomite Mountains (NE-Italy), one of the world's most conspicuous landscapes and part of the UNESCO world heritage list. Because of their unique geological composition the Dolomites provide a natural laboratory where nearly all kind of mass wasting processes, in all dimensions, can be investigated. Simplified there are thick, rigid carbonatic successions (Triassic-Jurassic) resting on and interfingering with relatively weak successions of shallow marine clastic and of pelagic sediments. In some areas even volcanic successions and crystalline basement rocks are outcropped. Hugh rockslides and long run-out rock avalanches are limited to the carbonates and volcanic rocks. The superposition of Middle and Upper Triassic reefs, showing brittle deformation behaviour, above weak successions of evaporites, clays and marls, characterised by ductile deformation behaviour, leads to a classical "hard on soft" situation. The observable results are rockslides and rock avalanches of several hundred millions of m³ in volume, large scale rock toppling and rock flows and deep-seated gravitational slope deformations (DSGSD). Within the weak successions slow moving rotational landslides and large dimensional earthflows are very common. We focused our research on an area of about 40*40km within the Western and Northern Dolomites, where an inventory of the major gravitational mass movements has been compiled. We combined detailed geological maps with high resolution DEMs and extensive fieldwork data within a GIS-system. The different processes have been characterised and classified based on kinematic criteria, dimension and involved material. Altogether the database consists of 186 entries. Most frequently are landslides and earthflows (146) followed by catastrophic rockslides and rock avalanches (26) and DSGSDs (14). The spatial distribution of the mapped processes has been analysed in terms of the main geomorphological and geological characteristics, and of their clustering. For some of the most impressive sites age data has been established and allows a supra-regional comparison. For each type of investigated mass movement we present an exemplary case study that shows the most important features of the major slope failures within the Dolomites.

Pretest parametric calculations for the heated pillar experiment in the WIPP In-Situ Experimental Area

DOE Office of Scientific and Technical Information (OSTI.GOV)

Branstetter, L.J.

Results are presented for a pretest parametric study of several configurations and heat loads for the heated pillar experiment (Room H) in the Waste Isolation Pilot Plant (WIPP) In Situ Experimental Area. The purpose of this study is to serve as a basis for selection of a final experiment geometry and heat load. The experiment consists of a pillar of undisturbed rock salt surrounded by an excavated annular room. The pillar surface is covered by a blanket heat source which is externally insulated. A total of five thermal and ten structural calculations are described in a four to five yearmore » experimental time frame. Results are presented which include relevant temperature-time histories, deformations, rock salt stress component and effective stress profiles, and maximum stresses in anhydrite layers which are in close proximity to the room. Also included are predicted contours of a conservative post-processed measure of potential salt failure. Observed displacement histories are seen to be highly dependent on pillar and room height, but insensitive to other geometrical variations. The use of a tensile cutoff across slidelines is seen to produce more accurate predictions of anhydrite maximum stress, but to have little effect on rock salt stresses. The potential for salt failure is seen to be small in each case for the time frame of interest, and is only seen at longer times in the center of the room floor.« less

In-situ stressing of rock: Observation of infrared emission prior to failure

NASA Astrophysics Data System (ADS)

Dahlgren, R.; Freund, F. T.; Momayez, M.; Bleier, T. E.; Dunson, C.; Joggerst, P.; Jones, K.; Wang, S.

2009-12-01

Blocks of igneous rocks such as anorthosite and granite subjected at one end to uniaxial stress have been shown to emit a small but distinct excess amount of infrared (IR) light (Freund, F. T., et al, JASTP, 71, 2009). This anomalous IR emission arises from the radiative de-excitation of electron vacancy defects, which, upon stress-activation, flow into the unstressed portion and recombine at the surface. This non-thermal IR emission occurs in the 8 μm to 14 μm wavelength region. Field experiments are performed by slowly stressing large boulders and monitoring the IR emission in situ with a Bruker EM27 Fourier Transform Infrared (FTIR) spectrometer. The boulders are prepared by drilling four blind holes into the rock, 50-100 cm deep, in an array roughly parallel to, and behind, the surface from where the IR emission is monitored. Any debris and water is blown out of the boreholes with compressed air, and the rock is given time to dry and relax from drilling-induced stresses. The holes are then filled with grout that expands upon curing, creating an increasing radial pressure of up to 5 × 103 t/m2. The experiments were carried out with two large granite boulders, one of about 30 t of hard (over 150 MPa) granite at the University of Arizona’s Henry "Hank" Grunstedt San Xavier Mining Laboratory, located in the copper mining district near Tucson, AZ and the other of about 7 t of weathered granite in the Sierra Nevada foothills near Oakhurst, CA. The Bruker EM27 FTIR spectrometer equipped with a 20 cm reflective telescope collects the IR emission from a safe distance at a rate of a full 4-16 µm spectrum every 30 sec. After recording baseline data, the grout was mixed with water and poured into the holes as IR emission was monitored continuously until the experiment was terminated after rock failure. The time of failure is noted whenever the first acoustic or visual cues are sensed from the boulder. The IR data shows that after a period of quiescence, pronounced non-thermal IR emission is observed within minutes of the rock failure.

An overview of recent large landslides in northern British Columbia, Canada.

NASA Astrophysics Data System (ADS)

Geertsema, M.; Clague, J. J.; Schwab, J. W.; Evans, S. G.

2003-04-01

Within the last few decades, at least twenty-four, long-runout rapid landslides, each in excess of 1 million m^3, have occurred in northern British Columbia. Fifteen of the landslides have happened within the last 10 years alone. The landslides include low- gradient rapid flowslides in cohesive sediments, rock avalanches, and complex rock slide - flowslides and rock slide - debris flows. The flowslides have occurred in a variety of sediments, including glaciolacustrine deposits, clay-rich tills, and clay-rich colluvium. The rock failures have involved weak shales overlain by sandstone, and volcanic rocks. We are cataloguing these landslides in a compendium of natural hazards for northern British Columbia. Pre- and post-landslide aerial photographs have been obtained for fifteen of the landslides, and detailed topographic maps have been generated from these photographs. In addition we have determined soil properties, including Atterberg tests for six of the flowslides. The rock avalanches occur in three types of settings: (1) dip slopes in sedimentary rocks in the Rocky Mountain foothills; (2) escarpments of flat-lying sedimentary rocks where spreading is happening; and (3) unstable cirque walls. Infrastructure and resources at risk from these types of large landslides include settlements, forest roads and highways, pipelines, fish habitat, forests, and farmland. One rock avalanche terminated within 2 km of the Alaska Highway, and a rock slide came within a few kilometres of a farm house. Most of these landslides have impounded streams or rivers, thus the hazard associated with upstream inundation and catastrophic dam failure must also be considered. There appears to be an increase in the frequency of large landslides in northern British Columbia. Is this due to climate change? Can we expect this trend to continue?

Damage evolution of bi-body model composed of weakly cemented soft rock and coal considering different interface effect.

PubMed

Zhao, Zenghui; Lv, Xianzhou; Wang, Weiming; Tan, Yunliang

2016-01-01

Considering the structure effect of tunnel stability in western mining of China, three typical kinds of numerical model were respectively built as follows based on the strain softening constitutive model and linear elastic-perfectly plastic model for soft rock and interface: R-M, R-C(s)-M and R-C(w)-M. Calculation results revealed that the stress-strain relation and failure characteristics of the three models vary between each other. The combination model without interface or with a strong interface presented continuous failure, while weak interface exhibited 'cut off' effect. Thus, conceptual models of bi-material model and bi-body model were established. Then numerical experiments of tri-axial compression were carried out for the two models. The relationships between stress evolution, failure zone and deformation rate fluctuations as well as the displacement of interface were detailed analyzed. Results show that two breakaway points of deformation rate actually demonstrate the starting and penetration of the main rupture, respectively. It is distinguishable due to the large fluctuation. The bi-material model shows general continuous failure while bi-body model shows 'V' type shear zone in weak body and failure in strong body near the interface due to the interface effect. With the increasing of confining pressure, the 'cut off' effect of weak interface is not obvious. These conclusions lay the theoretical foundation for further development of constitutive model for soft rock-coal combination body.

Self-ordering and complexity in epizonal mineral deposits

USGS Publications Warehouse

Henley, Richard W.; Berger, Byron R.

2000-01-01

Giant deposits are relatively rare and develop where efficient metal deposition is spatially focused by repetitive brittle failure in active fault arrays. Some brief case histories are provided for epithermal, replacement, and porphyry mineralization. These highlight how rock competency contrasts and feedback between processes, rather than any single component of a hydrothermal system, govern the size of individual deposits. In turn, the recognition of the probabilistic nature of mineralization provides a firmer foundation through which exploration investment and risk management decisions can be made.

Emplacement of rock avalanche material across saturated sediments, Southern Alp, New Zealand

NASA Astrophysics Data System (ADS)

Dufresne, A.; Davies, T. R.; McSaveney, M. J.

2012-04-01

The spreading of material from slope failure events is not only influenced by the volume and nature of the source material and the local topography, but also by the materials encountered in the runout path. In this study, evidence of complex interactions between rock avalanche and sedimentary runout path material were investigated at the 45 x 106 m3 long-runout (L: 4.8 km) Round Top rock avalanche deposit, New Zealand. It was sourced within myolinitic schists of the active strike-slip Alpine Fault. The narrow and in-failure-direction elongate source scarp is deep-seated, indicating slope failure was triggered by strong seismic activity. The most striking morphological deposit features are longitudinal ridges aligned radially to source. Trenching and geophysical surveys show bulldozed and sheared substrate material at ridge termini and laterally displaced sedimentary strata. The substrate failed at a minimum depth of 3 m indicating a ploughing motion of the ridges into the saturated material below. Internal avalanche compression features suggest deceleration behind the bulldozed substrate obstacle. Contorted fabric in material ahead of the ridge document substrate disruption by the overriding avalanche material deposited as the next down-motion hummock. Comparison with rock avalanches of similar volume but different emplacement environments places Round Top between longer runout avalanches emplaced over e.g. playa lake sediments and those with shorter travel distances, whose runout was apparently retarded by topographic obstacles or that entrained high-friction debris. These empirical observations indicate the importance of runout path materials on tentative trends in rock avalanche emplacement dynamics and runout behaviour.

Rock strength measurements on Archaean basement granitoids recovered from scientific drilling in the active Koyna seismogenic zone, western India

NASA Astrophysics Data System (ADS)

Goswami, Deepjyoti; Akkiraju, Vyasulu V.; Misra, Surajit; Roy, Sukanta; Singh, Santosh K.; Sinha, Amalendu; Gupta, Harsh; Bansal, B. K.; Nayak, Shailesh

2017-08-01

Reservoir triggered earthquakes have been occurring in the Koyna area, western India for the past five decades. Triaxial tests carried out on 181 core samples of Archaean granitoids underlying the Deccan Traps provide valuable constraints on rock strength properties in the Koyna seismogenic zone for the first time. The data include measurements on granite gneiss, granite, migmatitic gneiss and mylonitised granite gneiss obtained from boreholes KBH-3, KBH-4A, KBH-5 and KBH-7 located in the western and eastern margins of the seismic zone. Salient results are as follows. (i) Increase of rock strength with increasing confining pressure allow determination of the linearized failure envelopes from which the cohesive strength and angle of internal friction are calculated. (ii) Variable differential stresses at different depths are the manifestations of deformation partitioning in close association of fault zone(s) or localized fracture zones. (iii) Fractures controlled by naturally developed weak planes such as cleavage and fabric directly affect the rock strength properties, but the majority of failure planes developed during triaxial tests is not consistent with the orientations of pre-existing weak planes. The failure planes may, therefore, represent other planes of weakness induced by ongoing seismic activity. (iv) Stress-strain curves confirm that axial deformation is controlled by the varying intensity of pre-existing shear in the granitoids, viz., mylonite, granite gneiss and migmatitic gneiss. (v) Frequent occurrences of low magnitude earthquakes may be attributed to low and variable rock strength of the granitoids, which, in turn, is modified by successive seismic events.

Landslides triggered by the 8 October 2005 Kashmir earthquake

USGS Publications Warehouse

Owen, L.A.; Kamp, U.; Khattak, G.A.; Harp, E.L.; Keefer, D.K.; Bauer, M.A.

2008-01-01

The 8 October 2005 Kashmir earthquake triggered several thousand landslides. These were mainly rock falls and debris falls, although translational rock and debris slides also occurred. In addition, a sturzstrom (debris avalanche) comprising ??? 80??million m3 buried four villages and blocked streams to create two lakes. Although landsliding occurred throughout the region, covering an area of > 7500??km2, the failures were highly concentrated, associated with six geomorphic-geologic-anthropogenic settings, including natural failures in (1) highly fractured carbonate rocks comprising the lowest beds in the hanging wall of the likely earthquake fault; (2) Tertiary siliciclastic rocks along antecedent drainages that traverse the Hazara-Kashmir Syntaxis; (3) steep (> 50??) slopes comprising Precambrian and Lower Paleozoic rocks; (4) very steep (?? 50??) lower slopes of fluvially undercut Quaternary valley fills; and (5) ridges and spur crests. The sixth setting was associated with road construction. Extensive fissuring in many of the valley slopes together with the freshly mobilized landslide debris constitutes a potential hazard in the coming snowmelt and monsoon seasons. This study supports the view that earthquake-triggered landslides are highly concentrated in specific zones associated with the lithology, structure, geomorphology, topography, and human presence. ?? 2007 Elsevier B.V. All rights reserved.

Impact of ductility on hydraulic fracturing in shales

NASA Astrophysics Data System (ADS)

Auton, Lucy; MacMinn, Chris

2015-11-01

Hydraulic fracturing is a method for extracting natural gas and oil from low-permeability rocks such as shale via the injection of fluid at high pressure. This creates fractures in the rock, providing hydraulic access deeper into the reservoir and enabling gas to be collected from a larger region of the rock. Fracture is the tensile failure of a brittle material upon reaching a threshold tensile stress, but some shales have a high clay content and may yield plastically before fracturing. Plastic deformation is the shear failure of a ductile material, during which stress relaxes through irreversible rearrangements of the particles of the material. Here, we investigate the impact of the ductility of shales on hydraulic fracturing. We consider a simple, axisymmetric model for radially outward fluid injection from a wellbore into a ductile porous rock. We solve the model semi-analytically at steady state, and numerically in general. We find that plastic deformation greatly reduces the maximum tensile stress, and that this maximum stress does not always occur at the wellbore. These results imply that hydraulic fracturing may fail in ductile rocks, or that the required injection rate for fracking may be much larger than the rate predicted from purely elastic models.

Controls on size and occurrence of the largest sub-aerial landslide on Earth: Seymareh (Saidmarreh) landslide, Zagros fold-thrust belt, Iran

NASA Astrophysics Data System (ADS)

Roberts, N. J.; Evans, S. G.

2009-12-01

Gigantic (> 1 Gm3) landslides are high-magnitude, low-frequency extremes of mass movements. They are important factors in topographic evolution and hazard in mountain regions due to their magnitude. However, few examples exist for study because of their infrequency. Consequently, controls on the location and size gigantic landslides remain poorly understood. Re-examination of the Seymareh (Saidmarreh) rock avalanche, Zagros fold-thrust belt, shows it to be the largest sub-aerial landslide on Earth (initial failure volume 38 Gm3), thus representing the upper magnitude limit for terrestrial landslides. Detailed examination of the source area (including orbital remote sensing, geotechnical investigation and structural mapping) provides new insights into controls on the size and mobility of gigantic landslides. The gigantic Early Holocene rockslide initiated on the northeast limb of Kabir Kuh, the largest anticline in the Zagros fold-thrust belt, and involved the simultaneous failure of a rock mass measuring 15 km along strike. The rockslide transformed into a rock avalanche that ran-out 19.0 km, filling two adjacent valleys and overtopping an intervening low mountain ridge. The failure involved 220 m of competent jointed limestone (Asmari Formation) underlain by 580 m of weaker mudrock-dominated units. Geologic structure, geomechanical strength and topography of the source slope strongly controlled failure initiation. Extreme landslide dimensions resulted in part from extensive uniform pre-failure stability, produced by structural and topographic features related to the large scale of the Kabir Kuh anticline. High continuity bedding planes determined the large lateral extent along strike. Bedding normal joints, the breached nature of the anticline and fluvial undercutting at the slope toe accommodated expansive lateral, headscarp and toe release, respectively, necessary for extensive failure. Geomechanically weak units at depth aided the penetration of the failure surface into the source slope while low bedding dip (ca. 19°) allowed kinematic freedom of a particularly thick sequence to move downslope. Prevention of gradual rockmass removal by smaller-magnitude, more frequent denudation ensured its preservation for later simultaneous failure. The overall failure surface (11°) cut across weaker beds and finally breached the Asmari carapace by break-out at the base of the source slope. Relative relief of the source slope on Kabir Kuh was modest (1350 m on average) indicating that uniform structural and topographic conditions along strike, shallow bedding dips, and the geomechnical properties of the source rock mass were more important in determining the magnitude of the landslide that forms the upper magnitude limit for subaerial landslides.

Formation of slot-shaped borehole breakout within weakly cementedsandstones

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nakagawa, Seiji; Tomutsa, Liviu; Myer, Larry R.

2005-06-10

Breakout (wall failure) of boreholes within the earth can take several forms depending upon physical properties of the surrounding rock and the stress and flow conditions. Three distinctive modes of breakout are (I) extensile breakout observed in brittle rocks (e.g., Haimson and Herrick, 1986), (II) shear breakout in soft and clastic rocks (Zoback et al., 1985), and (III) fracture-like, slot-shaped breakout within highly porous granular rocks (Bessinger et al., 1997; Haimson and Song, 1998). During fluid production and injection within weakly cemented high-porosity rocks, the third type of failure could result in sustained and excessive sand production (disintegration of themore » rock's granular matrix and debris production). An objective of this research is to investigate the physical conditions that result in the formation of slot-shaped borehole breakout, via laboratory experiments. Our laboratory borehole breakout experiment was conducted using synthetic high-porosity sandstone with controlled porosity and strength. Block samples containing a single through-goring borehole were subjected to anisotropic stresses within a specially designed tri-axial loading cell. A series of studies was conducted to examine the impact of (1) stress anisotropy around the borehole, (2) rock strength, and (3) fluid flow rate within the borehole on the formation of slot-shaped borehole breakout. The geometry of the breakout was determined after the experiment using X-ray CT. As observed in other studies (Hamison and Song, 1998; Nakagawa and Myer, 2001), flow within a borehole plays a critical role in extending the slot-shaped breakout. The results of our experiments indicated that the width of the breakout was narrower for stronger rock, possibly due to higher resistance to erosion, and the orientation of the breakout plane was better defined for a borehole subjected to stronger stress anisotropy. In most cases, the breakout grew rapidly once the borehole wall started to fail. This 'run-away' failure growth is induced by monotonically increasing stress concentration at the breakout tips, although this effect may be augmented by the finite size of the sample.« less

Towards a Model of Reactive-Cracking: the Role of Reactions, Elasticity and Surface Energy Driven Flow in Poro-elastic Media

NASA Astrophysics Data System (ADS)

Evans, O.; Spiegelman, M. W.; Wilson, C. R.; Kelemen, P. B.

2016-12-01

Many critical processes can be described by reactive fluid flow in brittle media, including hydration/alteration of oceanic plates near spreading ridges, chemical weathering, and dehydration/decarbonation of subducting plates. Such hydration reactions can produce volume changes that may induce stresses large enough to drive fracture in the rock, in turn exposing new reactive surface and modifying the permeability. A better understanding of this potentially rich feedback could also be critical in the design of engineered systems for geologic carbon sequestration. To aid understanding of these processes we have developed a macroscopic continuum description of reactive fluid flow in an elastically deformable porous media. We explore the behaviour of this model by considering a simplified hydration reaction (e.g. olivine + H20 -> serpentine + brucite). In a closed system, these hydration reactions will continue to consume available fluids until the permeability reaches zero, leaving behind it a highly stressed residuum. Our model demonstrates this limiting behaviour, and that the elastic stresses generated are large enough to cause failure/fracture of the host rock. Whilst it is understood that `reactive fracture' is an important mechanism for the continued evolution of this process, it is also proposed that imbibition/surface energy driven flow may play a role. Through a simplified set of computational experiments, we investigate the relative roles of elasticity and surface energy in both a non-reactive purely poro-elastic framework, and then in the presence of reaction. We demonstrate that surface energy can drive rapid diffusion of porosity, thus allowing the reaction to propagate over larger areas. As we expect both surface energy and fracture/failure to be of importance in these processes, we plan to integrate the current model into one that allows for fracture once critical stresses are exceeded.

Pathophysiological effects of RhoA and Rho-associated kinase on cardiovascular system.

PubMed

Cai, Anping; Li, Liwen; Zhou, Yingling

2016-01-01

In past decades, growing evidence from basic and clinical researches reveal that small guanosine triphosphate binding protein ras homolog gene family, member A (RhoA) and its main effector Rho-associated kinase (ROCK) play central and complex roles in cardiovascular systems, and increasing RhoA and ROCK activity is associated with a broad range of cardiovascular diseases such as congestive heart failure, atherosclerosis, and hypertension. Favorable outcomes have been observed with ROCK inhibitors treatment. In this review, we briefly summarize the pathophysiological roles of RhoA/ROCK signaling pathway on cardiovascular system, displaying the potential benefits in the cardiovascular system with controlling RhoA/ROCK signaling pathway.

Coastal cliffs, rock-slope failures and Late Quaternary transgressions of the Black Sea along southern Crimea

NASA Astrophysics Data System (ADS)

Pánek, Tomáš; Lenart, Jan; Hradecký, Jan; Hercman, Helena; Braucher, Règis; Šilhán, Karel; Škarpich, Václav

2018-02-01

Rock-slope failures represent a significant hazard along global coastlines, but their chronology remains poorly documented. Here, we focus on the geomorphology and chronology of giant rockslides affecting the Crimean Mountains along the Black Sea coast. Geomorphic evidence suggests that high (>100 m) limestone cliffs flanking the southern slopes of the Crimean Mountains are scarps of rockslides nested within larger deep-seated gravitational slope deformations (DSGSDs). Such pervasive slope failures originated due to lateral spreading of intensively faulted Late Jurassic carbonate blocks moving atop weak/plastic Late Triassic flysch and tuff layers. By introducing a dating strategy relying on the combination of the uranium-thorium dating (U-Th) of exposed calcareous speleothems covering the landslide scarps with the 36Cl exposure dating of rock walls, we are able to approximate the time interval between the origin of incipient crevices and the final collapse of limestone blocks that exposed the cliff faces. For the three representative large-scale rockslides between the towns of Foros and Yalta, the initiation of the DSGSDs as evidenced by the widening of crevices and the onset of speleothem accumulation was >300 ka BP, but the recent cliff morphology along the coast is the result of Late Pleistocene/Holocene failures spanning ∼20-0.5 ka BP. The exposures of rockslide scarps occurred mostly at ∼20-15, ∼8, ∼5-4 and ∼2-0.5 ka, which substantially coincide with the last major Black Sea transgressions and/or more humid Holocene intervals. Our study suggests that before ultimate fast and/or catastrophic slope failures, the relaxation of rock massifs correlative with karstification, cracks opening, and incipient sliding lasted on the order of 104-105 years. Rapid Late Glacial/Holocene transgressions of the Black Sea likely represented the last impulse for the collapse of limestone blocks and the origin of giant rockslides, simultaneously affecting the majority of the SW coast of the Crimean Peninsula.

Energy monitoring and analysis during deformation of bedded-sandstone: use of acoustic emission.

PubMed

Wasantha, P L P; Ranjith, P G; Shao, S S

2014-01-01

This paper investigates the mechanical behaviour and energy releasing characteristics of bedded-sandstone with bedding layers in different orientations, under uniaxial compression. Cylindrical sandstone specimens (54 mm diameter and 108 mm height) with bedding layers inclined at angles of 10°, 20°, 35°, 55°, and 83° to the minor principal stress direction, were produced to perform a series of Uniaxial Compressive Strength (UCS) tests. One of the two identical sample sets was fully-saturated with water before testing and the other set was tested under dry conditions. An acoustic emission system was employed in all the testing to monitor the acoustic energy release during the whole deformation process of specimens. From the test results, the critical joint orientation was observed as 55° for both dry and saturated samples and the peak-strength losses due to water were 15.56%, 20.06%, 13.5%, 13.2%, and 13.52% for the bedding orientations 10°, 20°, 35°, 55°, and 83°, respectively. The failure mechanisms for the specimens with bedding layers in 10°, 20° orientations showed splitting type failure, while the specimens with bedding layers in 55°, 83° orientations were failed by sliding along a weaker bedding layer. The failure mechanism for the specimens with bedding layers in 35° orientation showed a mixed failure mode of both splitting and sliding types. Analysis of the acoustic energy, captured from the acoustic emission detection system, revealed that the acoustic energy release is considerably higher in dry specimens than that of the saturated specimens at any bedding orientation. In addition, higher energy release was observed for specimens with bedding layers oriented in shallow angles (which were undergoing splitting type failures), whereas specimens with steeply oriented bedding layers (which were undergoing sliding type failures) showed a comparatively less energy release under both dry and saturated conditions. Moreover, a considerable amount of energy dissipation before the ultimate failure was observed for specimens with bedding layers oriented in shallow angles under both dry and saturated conditions. These results confirm that when rock having bedding layers inclined in shallow angles the failures could be more violent and devastative than the failures of rock with steeply oriented bedding layers. Copyright © 2013 Elsevier B.V. All rights reserved.

Assessment of Slope Stability of Various Cut Slopes with Effects of Weathering by Using Slope Stability Probability Classification (SSPC)

NASA Astrophysics Data System (ADS)

Ersöz, Timur; Topal, Tamer

2017-04-01

Rocks containing pore spaces, fractures, joints, bedding planes and faults are prone to weathering due to temperature differences, wetting-drying, chemistry of solutions absorbed, and other physical and chemical agents. Especially cut slopes are very sensitive to weathering activities because of disturbed rock mass and topographical condition by excavation. During and right after an excavation process of a cut slope, weathering and erosion may act on this newly exposed rock material. These acting on the material may degrade and change its properties and the stability of the cut slope in its engineering lifetime. In this study, the effect of physical and chemical weathering agents on shear strength parameters of the rocks are investigated in order to observe the differences between weathered and unweathered rocks. Also, slope stability assessment of cut slopes affected by these weathering agents which may disturb the parameters like strength, cohesion, internal friction angle, unit weight, water absorption and porosity are studied. In order to compare the condition of the rock materials and analyze the slope stability, the parameters of weathered and fresh rock materials are found with in-situ tests such as Schmidt hammer and laboratory tests like uniaxial compressive strength, point load and direct shear. Moreover, slake durability and methylene blue tests are applied to investigate the response of the rock to weathering and presence of clays in rock materials, respectively. In addition to these studies, both rock strength parameters and any kind of failure mechanism are determined by probabilistic approach with the help of SSPC system. With these observations, the performances of the weathered and fresh zones of the cut slopes are evaluated and 2-D slope stability analysis are modeled with further recommendations for the cut slopes. Keywords: 2-D Modeling, Rock Strength, Slope Stability, SSPC, Weathering

Identification of a Suitable 3D Printing Material for Mimicking Brittle and Hard Rocks and Its Brittleness Enhancements

NASA Astrophysics Data System (ADS)

Zhou, T.; Zhu, J. B.

2018-03-01

Three-dimensional printing (3DP) is a computer-controlled additive manufacturing technique which is able to repeatedly and accurately fabricate objects with complicated geometry and internal structures. After 30 years of fast development, 3DP has become a mainstream manufacturing process in various fields. This study focuses on identifying the most suitable 3DP material from five targeted available 3DP materials, i.e. ceramics, gypsum, PMMA (poly(methyl methacrylate)), SR20 (acrylic copolymer) and resin (Accura® 60), to simulate brittle and hard rocks. Firstly, uniaxial compression tests were performed to determine the mechanical properties and failure patterns of the 3DP samples fabricated by those five materials. Experimental results indicate that among current 3DP techniques, the resin produced via stereolithography (SLA) is the most suitable 3DP material for mimicking brittle and hard rocks, although its brittleness needs to be improved. Subsequently, three methods including freezing, incorporation of internal macro-crack and addition of micro-defects were adopted to enhance the brittleness of the 3DP resin, followed by uniaxial compression tests on the treated samples. Experimental results reveal that 3DP resin samples with the suggested treatments exhibited brittle properties and behaved similarly to natural rocks. Finally, some prospective improvements which can be used to facilitate the application of 3DP techniques to rock mechanics were also discussed. The findings of this paper could contribute to promoting the application of 3DP technique in rock mechanics.

Geometrical properties of a discontinuity network in gneissic rock, a case study in high alpine terrain

NASA Astrophysics Data System (ADS)

Koppensteiner, Matthias; Zangerl, Christian

2017-04-01

For the purposes of estimating slope stability and investigating landslide formation processes, it is indispensable to obtain information about the discontinuity properties of the rock mass. These properties control failure processes, deformation behaviour and groundwater flow. Scanline measurements represent a systematic surveying method, however they make certain demands in case of natural outcorps in a high alpine terrain. The performance of the scanline method is tested and the thereby obtained and evaluated data is compared to findings from other studies. An area of a well exposed, fractured rock mass composed of granodioritic gneisses in the Oetztal-Stubai crytalline basement of the Alps (Austria) has been chosen to perform the investigations. Eight scanlines have been measured on a single hillside with varying lengths between 8 and 30 meters. The orientations of the scanlines have been varied in order to minimize the sampling bias associated with the angle between the scanlines and the intersected discontinuities. For every intersecting discontinuity at a certain tape length, the orientation, the trace length and the terminations of the trace have been recorded. Primarily, the discontinuity data from all scanlines have been analyzed with the software package Dips (Rocscience, 1989) in order to determine their allocation in sets. For the evaluation of the spacing and trace length properties, two scripts have been developed in the language Matlab (The MathWorks, 1984) to faciliate setwise processing of the entire dataset. Variation of the scanline directions and lengths returned homogeneous sample sizes for the individual discontinuity sets. Both, normal spacings and trace lengths show negative exponential distributions for all sets. A comparison of four different methods to estimate trace lengths show that the result is highly dependent on the chosen method itself. However, when the relation of the results for the respective sets within one of the methods is considered, the consistency is obvious. Scanline measurements and analyses provide siginificant results for discontinuity properties under the described circumstances. Considering sampling biases, the obtained dataset is even benefiting from the randomized sampling process, due to the natural terrain. The scanline survey provides a statistical database which can be used for rock mass characterization. Geometrical rock mass characterization is essential to model the in-situ block size distribution, to estimate the degree of fracturing and rock mass anisotropy for quarry oder tunnelling projects or define the mechanical rock mass properties based on classifications systems. The study should contribute a reference for the development and application of other methods for investigating discontinuity properties in instable rock masses.

High Strain Rate Testing of Rocks using a Split-Hopkinson-Pressure Bar

NASA Astrophysics Data System (ADS)

Zwiessler, Ruprecht; Kenkmann, Thomas; Poelchau, Michael; Nau, Siegfried; Hess, Sebastian

2016-04-01

Dynamic mechanical testing of rocks is important to define the onset of rate dependency of brittle failure. The strain rate dependency occurs through the propagation velocity limit (Rayleigh wave speed) of cracks and their reduced ability to coalesce, which, in turn, significantly increases the strength of the rock. We use a newly developed pressurized air driven Split-Hopkinson-Pressure Bar (SHPB), that is specifically designed for the investigation of high strain rate testing of rocks, consisting of several 10 to 50 cm long strikers and bar components of 50 mm in diameter and 2.5 meters in length each. The whole set up, composed of striker, incident- and transmission bar is available in aluminum, titanium and maraging steel to minimize the acoustic impedance contrast, determined by the change of density and speed of sound, to the specific rock of investigation. Dynamic mechanical parameters are obtained in compression as well as in spallation configuration, covering a wide spectrum from intermediate to high strain rates (100-103 s-1). In SHPB experiments [1] one-dimensional longitudinal compressive pulses of diverse shapes and lengths - formed with pulse shapers - are used to generate a variety of loading histories under 1D states of stress in cylindrical rock samples, in order to measure the respective stress-strain response at specific strain rates. Subsequent microstructural analysis of the deformed samples is aimed at quantification fracture orientation, fracture pattern, fracture density, and fracture surface properties as a function of the loading rate. Linking mechanical and microstructural data to natural dynamic deformation processes has relevance for the understanding of earthquakes, landslides, impacts, and has several rock engineering applications. For instance, experiments on dynamic fragmentation help to unravel super-shear rupture events that pervasively pulverize rocks up to several hundred meters from the fault core [2, 3, 4]. The dynamic, strain rate dependent behavior with strongly increasing strength and changing fracturing process has not been consequently considered in modeling of geo-hazards such as earthquakes, rock falls, landslides or even meteorite impacts [5]. Incorporation of dynamic material data therefore will contribute to improvements of forecast models and the understanding of fast geodynamic processes. References [1] Zhang, Q. B. & Zhao, J. (2013). A Review of Dynamic Experimental Techniques and Mechanical Behaviour of Rock Materials. Rock Mech Rock Eng. DOI 10.1007/s00603-013-0463-y [2] Doan, M. L., & Gary, G. (2009). Rock pulverization at high strain rate near the San Andreas fault. Nature Geosci., 2, 709-712. [3] Reches, Z. E., & Dewers, T. A. (2005). Gouge formation by dynamic pulverization during earthquake rupture. Earth Planet. Sci. Lett., 235, 361-374. [4] Fondriest, M., Aretusini, S., Di Toro, G., & Smith, S. A. (2015). Fracturing and rock pulverization along an exhumed seismogenic fault zone in dolostones: The Foiana Fault Zone (Southern Alps, Italy). Tectonophys.654, 56-74. [5] Kenkmann, T., Poelchau, M. H., & Wulf, G. (2014). Structural Geology of impact craters. J. .Struct. Geol., 62, 156-182.

Investigation of intact rock geomechanical parameters' effects on commercial blocks' productivity within stone reserves: A case history of some quarries in Isfahan, Iran

NASA Astrophysics Data System (ADS)

Yarahmadi, Reza; Bagherpour, Raheb; Tabaei, Morteza; Sousa, Luis M. O.

2017-10-01

One of the common methods to determine commercial blocks productivity (CBP) in reserves of dimension stone is through the study of the discontinuities' network. However, this determination remains a difficult task due to geographical heterogeneity and lack of access to all reserves' formations. This study presents a new method based on various geomechanical tests performed on intact rocks that assessed the CBP of a dimension stones' rock mass. Assuming that a dimension stone's rock mass comprised a large block of an intact rock, due to tectonics, the geomechanical properties of this block had direct effects on the discontinuities created within it. Therefore, the geomechanical properties of the intact rock may be related to the CBP of a stone reserve. Based on this factor, this study explored the relationship among some geomechanical properties, including failure angle, uniaxial compressive strength, and modulus of elasticity, and CBP by using data acquired from 21 dimension stone quarries consisting of travertine, marble, and onyx groups. According to the results obtained from the analysis of the Isfahan province's Iranian quarries, failure angle was not highly related to the reserve's CBP. In marble quarries, CBP may decrease, if the compressive strength of an intact rock exceeds 60 MPa. Among the studied parameters, the saturated-to-dry ratio's modulus of elasticity had the greatest relationship to the CBP. Generally, the presented diagrams displayed that the correlation between geomechanical properties and the CBP were an appropriate guide in determining the potential cost-effectiveness of a accessing a particular rock reserve during the early exploration phase.

Ferguson rock slide buries California State Highway near Yosemite National Park

USGS Publications Warehouse

Harp, Edwin L.; Reid, Mark E.; Godt, Jonathan W.; DeGraff, Jerome V.; Gallegos, Alan J.

2008-01-01

During spring 2006, talus from the toe area of a rock-block slide of about 800,000 m3 buried California State Highway 140, one of the main routes into heavily-visited Yosemite National Park, USA. Closure of the highway for 92 days caused business losses of about 4.8 million USD. The rock slide, composed of slate and phyllite, moved slowly downslope from April to June 2006, creating a fresh head scarp with 9-12 m of displacement. Movement of the main rock slide, a re-activation of an older slide, was triggered by an exceptionally wet spring 2006, following a very wet spring 2005. As of autumn 2006, most of the main slide appeared to be at rest, although rocks occasionally continued to fall from steep, fractured rock masses at the toe area of the slide. Future behavior of the slide is difficult to predict, but possible scenarios range from continued scattered rock fall to complete rapid failure of the entire mass. Although unlikely except under very destabilizing circumstances, a worst-case, rapid failure of the entire rock slide could extend across the Merced River, damming the river and creating a reservoir. As a temporary measure, traffic has been rerouted to the opposite side of the Merced River at about the same elevation as the buried section of Highway 140. A state-of-the-art monitoring system has been installed to detect movement in the steep talus slope, movement of the main slide mass, local strong ground motion from regional earthquakes, and sudden changes in stream levels, possibly indicating damming of the river by slide material.

A mechanism for high wall-rock velocities in rockbursts

USGS Publications Warehouse

McGarr, A.

1997-01-01

Considerable evidence has been reported for wall-rock velocities during rockbursts in deep gold mines that are substantially greater than ground velocities associated with the primary seismic events. Whereas varied evidence suggests that slip across a fault at the source of an event generates nearby particle velocities of, at most, several m/s, numerous observations, in nearby damaged tunnels, for instance, imply wall-rock velocities of the order of 10 m/s and greater. The common observation of slab buckling or breakouts in the sidewalls of damaged excavations suggests that slab flexure may be the mechanism for causing high rock ejection velocities. Following its formation, a sidewall slab buckles, causing the flexure to increase until the stress generated by flexure reaches the limit 5 that can be supported by the sidewall rock. I assume here that S is the uniaxial compressive strength. Once the flexural stress exceeds S, presumably due to the additional load imposed by a nearby seismic event, the slab fractures and unflexes violently. The peak wall-rock velocity v thereby generated is given by v=(3 + 1-??2/2)1 2 S/?????E for rock of density ??, Young's modulus E, and Poisson's ratio ??. Typical values of these rock properties for the deep gold mines of South Africa yield v= 26 m/s and for especially strong quartzites encountered in these same mines, v> 50m/s. Even though this slab buckling process leads to remarkably high ejection velocities and violent damage in excavations, the energy released during this failure is only a tiny fraction of that released in the primary seismic event, typically of magnitude 2 or greater.

THERMO-HYDRO-MECHANICAL MODELING OF WORKING FLUID INJECTION AND THERMAL ENERGY EXTRACTION IN EGS FRACTURES AND ROCK MATRIX

DOE Office of Scientific and Technical Information (OSTI.GOV)

Robert Podgorney; Chuan Lu; Hai Huang

2012-01-01

Development of enhanced geothermal systems (EGS) will require creation of a reservoir of sufficient volume to enable commercial-scale heat transfer from the reservoir rocks to the working fluid. A key assumption associated with reservoir creation/stimulation is that sufficient rock volumes can be hydraulically fractured via both tensile and shear failure, and more importantly by reactivation of naturally existing fractures (by shearing), to create the reservoir. The advancement of EGS greatly depends on our understanding of the dynamics of the intimately coupled rock-fracture-fluid-heat system and our ability to reliably predict how reservoirs behave under stimulation and production. Reliable performance predictions ofmore » EGS reservoirs require accurate and robust modeling for strongly coupled thermal-hydrological-mechanical (THM) processes. Conventionally, these types of problems have been solved using operator-splitting methods, usually by coupling a subsurface flow and heat transport simulators with a solid mechanics simulator via input files. An alternative approach is to solve the system of nonlinear partial differential equations that govern multiphase fluid flow, heat transport, and rock mechanics simultaneously, using a fully coupled, fully implicit solution procedure, in which all solution variables (pressure, enthalpy, and rock displacement fields) are solved simultaneously. This paper describes numerical simulations used to investigate the poro- and thermal- elastic effects of working fluid injection and thermal energy extraction on the properties of the fractures and rock matrix of a hypothetical EGS reservoir, using a novel simulation software FALCON (Podgorney et al., 2011), a finite element based simulator solving fully coupled multiphase fluid flow, heat transport, rock deformation, and fracturing using a global implicit approach. Investigations are also conducted on how these poro- and thermal-elastic effects are related to fracture permeability evolution.« less

Chronology of rock falls and slides in a desert mountain range: Case study from the Sonoran Desert in south-central Arizona

NASA Astrophysics Data System (ADS)

Dorn, Ronald I.

2014-10-01

In order to respond to the general paucity of information on the chronology of ubiquitous small rock falls and slides that litter the slopes of desert mountain ranges, a case study in the Sonoran Desert reveals new insight into the desert geomorphology of mountain slopes. Rock falls and rock slides in the McDowell Mountains that abut metropolitan Phoenix, USA, fall in three chronometric groupings dated by conventional radiocarbon and rock varnish microlamination methods. First, the oldest events are > 74 ka and take the form of stable colluvial boulder fields - positive relief features that are tens of meters long and a few meters wide. Second, randomly sampled slides and falls of various sizes and positions wasted during wetter periods of the terminal Pleistocene and Holocene. Third, an anomalous clustering of slides and falls occurred during the late Medieval Warm Period (Medieval Climatic Anomaly) when an extreme storm was a possible but unlikely trigger. One speculative hypothesis for the cluster of Medieval Warm Period events is that a small to moderate sized earthquake shook heavily shattered bedrock - close to failure - just enough to cause a spate of rock falls and slides. A second speculative hypothesis is that this dry period enhanced physical weathering processes such as dirt cracking. However, the reasons for the recent clustering of rock falls remain enigmatic. While the temporal distribution of slides and falls suggests a minimal hazard potential for homes and roads on the margins of the McDowell Mountains, this finding may not necessary match other desert ranges in metropolitan Phoenix or mountains with different rock types and structures that abut other arid urban centers.

Fault Damage Zone Permeability in Crystalline Rocks from Combined Field and Laboratory Measurements

NASA Astrophysics Data System (ADS)

Mitchell, T.; Faulkner, D.

2008-12-01

In nature, permeability is enhanced in the damage zone of faults, where fracturing occurs on a wide range of scales. Here we analyze the contribution of microfracture damage on the permeability of faults that cut through low porosity, crystalline rocks by combining field and laboratory measurements. Microfracture densities surrounding strike-slip faults with well-constrained displacements ranging over 3 orders of magnitude (~0.12 m - 5000 m) have been analyzed. The faults studied are excellently exposed within the Atacama Fault Zone, where exhumation from 6-10 km has occurred. Microfractures in the form of fluid inclusion planes (FIPs) show a log-linear decrease in fracture density with perpendicular distance from the fault core. Damage zone widths defined by the density of FIPs scale with fault displacement, and an empirical relationship for microfracture density distribution throughout the damage zone with displacement is derived. Damage zone rocks will have experienced differential stresses that were less than, but some proportion of, the failure stress. As such, permeability data from progressively loaded, initially intact laboratory samples, in the pre-failure region provide useful insights into fluid flow properties of various parts of the damage zone. The permeability evolution of initially intact crystalline rocks under increasing differential load leading to macroscopic failure was determined at water pore pressures of 50 MPa and effective pressure of 10 MPa. Permeability is seen to increase by up to, and over, two orders of magnitude prior to macroscopic failure. Further experiments were stopped at various points in the loading history in order to correlate microfracture density within the samples with permeability. By combining empirical relationships determined from both quantitative fieldwork and experiments we present a model that allows microfracture permeability distribution throughout the damage zone to be determined as function of increasing fault displacement.

Gravity-induced rock mass damage related to large en masse rockslides: Evidence from Vajont

NASA Astrophysics Data System (ADS)

Paronuzzi, Paolo; Bolla, Alberto

2015-04-01

The Vajont landslide is a well-known, reservoir-induced slope failure that occurred on 9 October 1963 and was characterized by an 'en masse' sliding motion that triggered various large waves, determining catastrophic consequences for the nearby territory and adjacent villages. During the Vajont dam construction, and especially after the disaster, some researchers identified widespread field evidence of heavy rock mass damage involving the presumed prehistoric rockslide and/or the 1963 failed mass. This paper describes evidence of heavy gravitational damage, including (i) folding, (ii) fracturing, (iii) faulting, and (iv) intact rock disintegration. The gravity-induced rock mass damage (GRMD) characterizes the remnants of the basal shear zone, still resting on the large detachment surface, and the 1963 failed rock mass. The comprehensive geological study of the 1963 Vajont landslide, based on the recently performed geomechanical survey (2006-present) and on the critical analysis of the past photographic documentation (1959-1964), allows us to recognize that most GRMD evidence is related to the prehistoric multistage Mt. Toc rockslide. The 1963 catastrophic en masse remobilization induced an increase to the prehistoric damage, reworking preexisting structures and creating additional gravity-driven features (folds, fractures, faults, and rock fragmentation). The gravity-induced damage was formed during the slope instability phases that preceded the collapse (static or quasi-static GRMD) and also as a consequence of the sliding motion and of the devastating impact between the failed blocks (dynamic GRMD). Gravitational damage originated various types of small drag folds such as flexures, concentric folds, chevron, and kink-box folds, all having a radius of 1-5 m. Large buckle folds (radius of 10-50 m) are related to the dynamic damage and were formed during the en masse motion as a consequence of deceleration and impact processes that involved the sliding mass. Prior to failure, unstable rock slopes can be affected by diffuse newly formed gravity-driven joints that are absent in the surrounding area and within the underlying bedrock, as the Vajont case history demonstrates (joint sets J9 and J10). These fractures, caused by critical tensile and shear stresses, represent an important mechanical clue to recognizing, on a geological basis, the instability condition of a rock slope under investigation. Owing to its complex geological evolution, the Vajont landslide is an outstanding example to help learn about cumulative GRMD effects that can accumulate over time when an ancient rockslide is further remobilized by a sudden en masse sliding motion.

Characterization of Unstable Rock Slopes Through Passive Seismic Measurements

NASA Astrophysics Data System (ADS)

Kleinbrod, U.; Burjanek, J.; Fäh, D.

2014-12-01

Catastrophic rock slope failures have high social impact, causing significant damage to infrastructure and many casualties throughout the world each year. Both detection and characterization of rock instabilities are therefore of key importance. An analysis of ambient vibrations of unstable rock slopes might be a new alternative to the already existing methods, e.g. geotechnical displacement measurements. Systematic measurements have been performed recently in Switzerland to study the seismic response of potential rockslides concerning a broad class of slope failure mechanisms and material conditions. Small aperture seismic arrays were deployed at sites of interest for a short period of time (several hours) in order to record ambient vibrations. Each measurement setup included a reference station, which was installed on a stable part close to the instability. Recorded ground motion is highly directional in the unstable parts of the rock slope, and significantly amplified with respect to stable areas. These effects are strongest at certain frequencies, which were identified as eigenfrequencies of the unstable rock mass. In most cases the directions of maximum amplification are perpendicular to open cracks and in good agreement with the deformation directions obtained by geodetic measurements. Such unique signatures might improve our understanding of slope structure and stability. Thus we link observed vibration characteristics with available results of detailed geological characterization. This is supported by numerical modeling of seismic wave propagation in fractured media with complex topography.For example, a potential relation between eigenfrequencies and unstable rock mass volume is investigated.

A Transversely Isotropic Thermo-mechanical Framework for Oil Shale

NASA Astrophysics Data System (ADS)

Semnani, S. J.; White, J. A.; Borja, R. I.

2014-12-01

The present study provides a thermo-mechanical framework for modeling the temperature dependent behavior of oil shale. As a result of heating, oil shale undergoes phase transformations, during which organic matter is converted to petroleum products, e.g. light oil, heavy oil, bitumen, and coke. The change in the constituents and microstructure of shale at high temperatures dramatically alters its mechanical behavior e.g. plastic deformations and strength, as demonstrated by triaxial tests conducted at multiple temperatures [1,2]. Accordingly, the present model formulates the effects of changes in the chemical constituents due to thermal loading. It is well known that due to the layered structure of shale its mechanical properties in the direction parallel to the bedding planes is significantly different from its properties in the perpendicular direction. Although isotropic models simplify the modeling process, they fail to accurately describe the mechanical behavior of these rocks. Therefore, many researchers have studied the anisotropic behavior of rocks, including shale [3]. The current study presents a framework to incorporate the effects of transverse isotropy within a thermo-mechanical formulation. The proposed constitutive model can be readily applied to existing finite element codes to predict the behavior of oil shale in applications such as in-situ retorting process and stability assessment in petroleum reservoirs. [1] Masri, M. et al."Experimental Study of the Thermomechanical Behavior of the Petroleum Reservoir." SPE Eastern Regional/AAPG Eastern Section Joint Meeting. Society of Petroleum Engineers, 2008. [2] Xu, B. et al. "Thermal impact on shale deformation/failure behaviors---laboratory studies." 45th US Rock Mechanics/Geomechanics Symposium. American Rock Mechanics Association, 2011. [3] Crook, AJL et al. "Development of an orthotropic 3D elastoplastic material model for shale." SPE/ISRM Rock Mechanics Conference. Society of Petroleum Engineers, 2002.

Experimental and Numerical Studies on Development of Fracture Process Zone (FPZ) in Rocks under Cyclic and Static Loadings

NASA Astrophysics Data System (ADS)

Ghamgosar, M.; Erarslan, N.

2016-03-01

The development of fracture process zones (FPZ) in the Cracked Chevron Notched Brazilian Disc (CCNBD) monsonite and Brisbane tuff specimens was investigated to evaluate the mechanical behaviour of brittle rocks under static and various cyclic loadings. An FPZ is a region that involves different types of damage around the pre-existing and/or stress-induced crack tips in engineering materials. This highly damaged area includes micro- and meso-cracks, which emerge prior to the main fracture growth or extension and ultimately coalescence to macrofractures, leading to the failure. The experiments and numerical simulations were designed for this study to investigate the following features of FPZ in rocks: (1) ligament connections and (2) microcracking and its coalescence in FPZ. A Computed Tomography (CT) scan technique was also used to investigate the FPZ behaviour in selected rock specimens. The CT scan results showed that the fracturing velocity is entirely dependent on the appropriate amount of fracture energy absorbed in rock specimens due to the change of frequency and amplitudes of the dynamic loading. Extended Finite Element Method (XFEM) was used to compute the displacements, tensile stress distribution and plastic energy dissipation around the propagating crack tip in FPZ. One of the most important observations, the shape of FPZ and its extension around the crack tip, was made using numerical and experimental results, which supported the CT scan results. When the static rupture and the cyclic rupture were compared, the main differences are twofold: (1) the number of fragments produced is much greater under cyclic loading than under static loading, and (2) intergranular cracks are formed due to particle breakage under cyclic loading compared with smooth and bright cracks along cleavage planes under static loading.

Experimental Microfracture Permeability Development in Crystalline Rocks Under Different Tectonic Stress Regimes

NASA Astrophysics Data System (ADS)

Faulkner, D. R.; Armitage, P. J.

2011-12-01

Geothermal fields rely on permeable fracture networks that can act for significant periods of time. In crystalline rocks, permeability may be stimulated by injections of fluid pressure at depth. We show how high-pressure laboratory experiments can be used to quantify the effects of different stress states on the permeability of two rocks; Darley Dale sandstone (~10-16 m2 permeability) and Westerly granite (~10-20 m2 permeability). It is well known that microfractures start to grow at stresses around one half of the failure stress. Failure in the experiments was reproduced in several ways: (1) by fixing σ3 and increasing σ1 - equivalent to a compressive or strike-slip tectonic regime (2) by fixing σ1 and decreasing σ3 - equivalent to an extensional tectonic regime (3) by increasing the pore fluid pressure at a fixed differential stress to simulate high pore fluid pressure failure, and (4) by fixing the mean stress while increasing σ1 and decreasing σ3 in sympathy. Permeability was monitored during all of these tests. From these tests we are able to quantify the relative contributions of mean stress, differential stress and pore fluid pressure on the permeability in the pre-failure region. This provides key data on the development of microfracture permeability that might be produced during the stimulation of geothermal fields during injection within different tectonic environments.

Rock Slope Monitoring from 4D Time-Lapse Structure from Motion Analysis

NASA Astrophysics Data System (ADS)

Kromer, Ryan; Abellan, Antonio; Chyz, Alex; Hutchinson, Jean

2017-04-01

Structure from Motion (SfM) photogrammetry has become an important tool for studying earth surface processes because of its flexibility, ease of use, low cost and its capability of producing high quality 3-D surface models. A major benefit of SfM is that model accuracy is fit for purpose and surveys can be designed to meet a large range of spatial and temporal scales. In the Earth sciences, research in time-lapse SfM photogrammetry or videogrammetry is an area that is difficult to undertake due to complexities in acquiring, processing and managing large 4D datasets and represents an area with significant advancement potential (Eltner et al. 2016). In this study, we investigate the potential of 4D time-lapse SfM to monitor unstable rock slopes. We tested an array of statically mounted cameras collecting time-lapse photos of a limestone rock slope located along a highway in Canada. Our setup consisted of 8 DSLR cameras with 50 mm prime lenses spaced 2-3 m apart at a distance of 10 m from the slope. The portion of the rock slope monitored was 20 m wide and 6 m high. We collected data in four phases, each having 50 photographs taken simultaneously by each camera. The first phase of photographs was taken of the stable slope. In each successive phase, we gradually moved small, discrete blocks within the rock slope by 5-15 mm, simulating pre-failure deformation of rockfall. During the last phase we also removed discrete rock blocks, simulating rockfall. We used Agisoft Photoscan's 4D processing functionality and timeline tools to create 3D point clouds from the time-lapse photographs. These tools have the benefit of attaining better accuracy photo alignments as a greater number of photos are used. For change detection, we used the 4D filtering and calibration technique proposed by Kromer et al. (2015), which takes advantage of high degrees of spatial and temporal point redundancy to decrease measurement uncertainty. Preliminary results show that it is possible to attain more accurate 3D models using time-lapse photos taken from an array of cameras than photos taken from a single camera from multiple positions. For this survey setup, it was possible to detect mm to cm level of changes, which is of sufficient accuracy to detect the pre-failure stage of rockfalls, as well as small rockfall events. Additionally, cameras mounted in a static array can be operated remotely and automatically. Time-lapse SfM photogrammetry can be a cost effective alternative to terrestrial laser scanning for rockfall prone areas and facilitates the study of surface processes with high spatial and temporal detail. We gratefully acknowledge support from the NSERC collaborative research and development grant. References Eltner, A., Kaiser, A., Castillo, C.; Rock, G., Neugirg, F., Abellán, A. Image-based surface reconstruction in geomorphometry—Merits, limits and developments. Earth Surf. Dyn. 2016, 4, 359-389. Kromer, R. A., Abellán, A., Hutchinson, D. J., Lato, M., Edwards, T., & Jaboyedoff, M. A 4D filtering and calibration technique for small-scale point cloud change detection with a terrestrial laser scanner. Remote Sensing 2015, 7(10), 13029-13052.

Fault growth and acoustic emissions in confined granite

USGS Publications Warehouse

Lockner, David A.; Byerlee, James D.

1992-01-01

The failure process in a brittle granite was studied by using acoustic emission techniques to obtain three dimensional locations of the microfracturing events. During a creep experiment the nucleation of faulting coincided with the onset of tertiary creep, but the development of the fault could not be followed because the failure occurred catastrophically. A technique has been developed that enables the failure process to be stabilized by controlling the axial stress to maintain a constant acoustic emission rate. As a result the post-failure stress-strain curve has been followed quasi-statically, extending to hours the fault growth process that normally would occur violently in a fraction of a second. The results from the rate-controlled experiments show that the fault plane nucleated at a point on the sample surface after the stress-strain curve reached its peak. Before nucleation, the microcrack growth was distributed throughout the sample. The fault plane then grew outward from the nucleation site and was accompanied by a gradual drop in stress. Acoustic emission locations showed that the fault propagated as a fracture front (process zone) with dimensions of 1 to 3 cm. As the fracture front passed by a given fixed point on the fault plane, the subsequent acoustic emission would drop. When growth was allowed to progress until the fault bisected the sample, the stress dropped to the frictional strength. These observations are in accord with the behavior predicted by Rudnicki and Rice's bifurcation analysis but conflict with experiments used to infer that shear localization would occur in brittle rock while the material is still hardening.

Fabric controls on the brittle failure of folded gneiss and schist

NASA Astrophysics Data System (ADS)

Agliardi, Federico; Zanchetta, Stefano; Crosta, Giovanni B.

2014-12-01

We experimentally studied the brittle failure behaviour of folded gneiss and schist. Rock fabric and petrography were characterised by meso-structural analyses, optical microscopy, X-ray diffraction, and SEM imaging. Uniaxial compression, triaxial compression and indirect tension laboratory tests were performed to characterise their strength and stress-strain behaviour. Fracture patterns generated in compression were resolved in 3D through X-ray computed tomography at different resolutions (30 to 625 μm). Uniaxial compression tests revealed relatively low and scattered values of unconfined compressive strength (UCS) and Young's modulus, with no obvious relationships with the orientation of foliation. Samples systematically failed in four brittle modes, involving different combinations of shear fractures along foliation or parallel to fold axial planes, or the development of cm-scale shear zones. Fracture quantification and microstructural analysis show that different failure modes occur depending on the mutual geometrical arrangement and degree of involvement of two distinct physical anisotropies, i.e. the foliation and the fold axial planes. The Axial Plane Anisotropy (APA) is related to micro-scale grain size reduction and shape preferred orientation within quartz-rich domains, and to mechanical rotation or initial crenulation cleavage within phyllosilicate-rich domains at fold hinge zones. In quartz-rich rocks (gneiss), fracture propagation through quartz aggregates forming the APA corresponds to higher fracture energy and strength than found for fracture through phyllosilicate-rich domains. This results in a strong dependence of strength on the failure mode. Conversely, in phyllosilicate-rich rocks (schist), all the failure modes are dominated by the strength of phyllosilicates, resulting in a sharp reduction of strength anisotropy.

Closed-Form Solutions for a Circular Tunnel in Elastic-Brittle-Plastic Ground with the Original and Generalized Hoek-Brown Failure Criteria

NASA Astrophysics Data System (ADS)

Chen, Ran; Tonon, Fulvio

2011-03-01

The paper presents a closed-form solution for the convergence curve of a circular tunnel in an elasto-brittle-plastic rock mass with both the Hoek-Brown and generalized Hoek-Brown failure criteria, and a linear flow rule, i.e., the ratio between the minor and major plastic strain increments is constant. The improvement over the original solution of Brown et al. (J Geotech Eng ASCE 109(1):15-39, 1983) consists of taking into account the elastic strain variation in the plastic annulus, which was assumed to be fixed in the original solution by Brown et al. The improvement over Carranza-Torres' solution (Int J Rock Mech Min Sci 41(Suppl 1):629-639, 2004) consists of providing a closed-form solution, rather than resorting to numerical integration of an ordinary differential equation. The presented solution, by rigorously following the theory of plasticity, takes into account that the elastic strain components change with radial and circumferential stress changes within the plastic annulus. For the original Hoek-Brown failure criterion, disregarding the elastic strain change leads to underestimate the convergence by up to 55%. For a rock mass failing according to the generalized Hoek-Brown failure criterion, using the original failure criterion leads to a high probability (97%) of underestimating the convergence by up to 100%. As a consequence, the onset or degree of squeezing may be underestimated, and the loading on the support/reinforcement calculated with the convergence/confinement method may be largely underestimated.

Deformation and failure of single- and multi-phase silicate liquids: seismic precursors and mechanical work

NASA Astrophysics Data System (ADS)

Vasseur, Jeremie; Lavallée, Yan; Hess, Kai-Uwe; Wassermann, Joachim; Dingwell, Donald B.

2013-04-01

Along with many others, volcanic unrest is regarded as a catastrophic material failure phenomenon and is often preceded by diverse precursory signals. Although a volcanic system intrinsically behave in a non-linear and stochastic way, these precursors display systematic evolutionary trends to upcoming eruptions. Seismic signals in particular are in general dramatically increasing prior to an eruption and have been extensively reported to show accelerating rates through time, as well as in the laboratory before failure of rock samples. At the lab-scale, acoustic emissions (AE) are high frequency transient stress waves used to track fracture initiation and propagation inside a rock sample. Synthesized glass samples featuring a range of porosities (0 - 30%) and natural rock samples from volcán de Colima, Mexico, have been failed under high temperature uniaxial compression experiments at constant stresses and strain rates. Using the monitored AEs and the generated mechanical work during deformation, we investigated the evolutionary trends of energy patterns associated to different degrees of heterogeneity. We observed that the failure of dense, poorly porous glasses is achieved by exceeding elevated strength and thus requires a significant accumulation of strain, meaning only pervasive small-scale cracking is occurring. More porous glasses as well as volcanic samples need much lower applied stress and deformation to fail, as fractures are nucleating, propagating and coalescing into localized large-scale cracks, taking the advantage of the existence of numerous defects (voids for glasses, voids and crystals for volcanic rocks). These observations demonstrate that the mechanical work generated through cracking is efficiently distributed inside denser and more homogeneous samples, as underlined by the overall lower AE energy released during experiments. In contrast, the quicker and larger AE energy released during the loading of heterogeneous samples shows that the mechanical work tends to concentrate in specific weak regions facilitating dynamical failure of the material through dissipation of the accumulated strain energy. Applying a statistical Global Linearization Method (GLM) in multi-phase silicate liquids samples leads to a maximum likelihood power-law fit of the accelerating rates of released AEs. The calculated α exponent of the famous empirical Failure Forecast Method (FFM) tends to decrease from 2 towards 1 with increasing porosity, suggesting a shift towards an idealized exponential-like acceleration. Single-phase silicate liquids behave more elastically during deformation without much cracking and suddenly releasing their accumulated strain energy at failure, implying less clear trends in monitored AEs. In a predictive prospective, these results support the fact that failure forecasting power is enhanced by the presence of heterogeneities inside a material.

An engineering rock classification to evaluate seismic rock-fall susceptibility and its application to the Wasatch Front

USGS Publications Warehouse

Harp, E.L.; Noble, M.A.

1993-01-01

Investigations of earthquakes world wide show that rock falls are the most abundant type of landslide that is triggered by earthquakes. An engineering classification originally used in tunnel design, known as the rock mass quality designation (Q), was modified for use in rating the susceptibility of rock slopes to seismically-induced failure. Analysis of rock-fall concentrations and Q-values for the 1980 earthquake sequence near Mammoth Lakes, California, defines a well-constrained upper bound that shows the number of rock falls per site decreases rapidly with increasing Q. Because of the similarities of lithology and slope between the Eastern Sierra Nevada Range near Mammoth Lakes and the Wasatch Front near Salt Lake City, Utah, the probabilities derived from analysis of the Mammoth Lakes region were used to predict rock-fall probabilities for rock slopes near Salt Lake City in response to a magnitude 6.0 earthquake. These predicted probabilities were then used to generalize zones of rock-fall susceptibility. -from Authors

Relative scale and the strength and deformability of rock masses

NASA Astrophysics Data System (ADS)

Schultz, Richard A.

1996-09-01

The strength and deformation of rocks depend strongly on the degree of fracturing, which can be assessed in the field and related systematically to these properties. Appropriate Mohr envelopes obtained from the Rock Mass Rating (RMR) classification system and the Hoek-Brown criterion for outcrops and other large-scale exposures of fractured rocks show that rock-mass cohesive strength, tensile strength, and unconfined compressive strength can be reduced by as much as a factor often relative to values for the unfractured material. The rock-mass deformation modulus is also reduced relative to Young's modulus. A "cook-book" example illustrates the use of RMR in field applications. The smaller values of rock-mass strength and deformability imply that there is a particular scale of observation whose identification is critical to applying laboratory measurements and associated failure criteria to geologic structures.

Debris-flow mobilization from landslides

USGS Publications Warehouse

Iverson, R.M.; Reid, M.E.; LaHusen, R.G.

1997-01-01

Field observations, laboratory experiments, and theoretical analyses indicate that landslides mobilize to form debris flows by three processes: (a) widespread Coulomb failure within a sloping soil, rock, or sediment mass, (b) partial or complete liquefaction of the mass by high pore-fluid pressures, and (c) conversion of landslide translational energy to internal vibrational energy (i.e. granular temperature). These processes can operate independently, but in many circumstances they appear to operate simultaneously and synergistically. Early work on debris-flow mobilization described a similar interplay of processes but relied on mechanical models in which debris behavior was assumed to be fixed and governed by a Bingham or Bagnold rheology. In contrast, this review emphasizes models in which debris behavior evolves in response to changing pore pressures and granular temperatures. One-dimensional infinite-slope models provide insight by quantifying how pore pressures and granular temperatures can influence the transition from Coulomb failure to liquefaction. Analyses of multidimensional experiments reveal complications ignored in one-dimensional models and demonstrate that debris-flow mobilization may occur by at least two distinct modes in the field.

Seismically induced rock slope failures resulting from topographic amplification of strong ground motions: The case of Pacoima Canyon, California

USGS Publications Warehouse

Sepulveda, S.A.; Murphy, W.; Jibson, R.W.; Petley, D.N.

2005-01-01

The 1994 Northridge earthquake (Mw = 6.7) triggered extensive rock slope failures in Pacoima Canyon, immediately north of Los Angeles, California. Pacoima Canyon is a narrow and steep canyon incised in gneissic and granitic rocks. Peak accelerations of nearly 1.6 g were recorded at a ridge that forms the left abutment of Pacoima Dam; peak accelerations at the bottom of the canyon were less than 0.5 g, suggesting the occurrence of topographic amplification. Topographic effects have been previously suggested to explain similarly high ground motions at the site during the 1971 (Mw = 6.7) San Fernando earthquake. Furthermore, high landslide concentrations observed in the area have been attributed to unusually strong ground motions rather than higher susceptibility to sliding compared with nearby zones. We conducted field investigations and slope stability back-analyses to confirm the impact of topographic amplification on the triggering of landslides during the 1994 earthquake. Our results suggest that the observed extensive rock sliding and falling would have not been possible under unamplified seismic conditions, which would have generated a significantly lower number of areas affected by landslides. In contrast, modelling slope stability using amplified ground shaking predicts slope failure distributions matching what occurred in 1994. This observation confirms a significant role for topographic amplification on the triggering of landslides at the site, and emphasises the need to select carefully the inputs for seismic slope stability analyses. ?? 2005 Elsevier B.V. All rights reserved.

Modelling of the CO2-Induced Degradation of a Fractured Caprock During Leakage: Potential for a Mechanical Self-Limiting Process

NASA Astrophysics Data System (ADS)

Rohmer, J.; Tremosa, J.; Marty, N. C. M.; Audigane, P.

2017-10-01

In the present study, we assess the potential for initiating ductile failure in a fractured caprock due to the chemical alteration of its mechanical properties under pressure increase induced by CO2 leakage and fixed in situ boundary conditions. In this view, 2D numerically coupled reactive-transport simulations were set up by using the Opalinus Clay formation as an analogue for a caprock layer. The fractured system was viewed as a compartmentalised system that consists of a main highly permeable pathway, a moderately permeable damage zone and the intact rock. The outputs of the numerical simulations (mineral fraction, porosity changes, gas saturation, pore-fluid pressure) were converted into parameter changes of the yield surface by viewing the rock material of the three compartments (fault, damage zone and intact rock) as a composite system that consists of a clayey solid material, pores and mineral inclusions (such as carbonate and quartz). Three alteration processes were considered: (1) the effect of the mineral fraction and porosity evolution on the yield surface, (2) changes in the resulting poro-elastic properties and (3) the suction effect, i.e. the bounding effect induced by the presence of two phases, water and CO2. Our numerical investigations showed that the decrease in the friction coefficient remained negligible during leakage, while the pre-consolidation stress mainly decreased. Consequently, the damage zone of the fractured system became more collapsible over time, which was driven by low-to-moderate pressure build-up of the fluid penetrating the fault (1 MPa in our case). For the considered case, the initiation of ductile failure is likely under conditions of fixed vertical stress and zero lateral strain. This process could potentially limit the spatial spreading of CO2-induced alteration, although this remains very site specific. We recommend that characterisation efforts be intensified to obtain better insight into the properties of fracture systems in caprock-like formations (with special attention to their initial over consolidation ratio).

Ferguson rock slide buries California State Highway near Yosemite National Park

USGS Publications Warehouse

Harp, E.L.; Reid, M.E.; Godt, J.W.; DeGraff, J.V.; Gallegos, A.J.

2008-01-01

During spring 2006, talus from the toe area of a rock-block slide of about 800,000 m3 buried California State Highway 140, one of the main routes into heavily-visited Yosemite National Park, USA. Closure of the highway for 92 days caused business losses of about 4.8 million USD. The rock slide, composed of slate and phyllite, moved slowly downslope from April to June 2006, creating a fresh head scarp with 9-12 m of displacement. Movement of the main rock slide, a re-activation of an older slide, was triggered by an exceptionally wet spring 2006, following a very wet spring 2005. As of autumn 2006, most of the main slide appeared to be at rest, although rocks occasionally continued to fall from steep, fractured rock masses at the toe area of the slide. Future behavior of the slide is difficult to predict, but possible scenarios range from continued scattered rock fall to complete rapid failure of the entire mass. Although unlikely except under very destabilizing circumstances, a worst-case, rapid failure of the entire rock slide could extend across the Merced River, damming the river and creating a reservoir. As a temporary measure, traffic has been rerouted to the opposite side of the Merced River at about the same elevation as the buried section of Highway 140. A state-of-the-art monitoring system has been installed to detect movement in the steep talus slope, movement of the main slide mass, local strong ground motion from regional earthquakes, and sudden changes in stream levels, possibly indicating damming of the river by slide material. ?? 2008 Springer-Verlag.

Frictional behaviour of sandstone: A sample-size dependent triaxial investigation

NASA Astrophysics Data System (ADS)

Roshan, Hamid; Masoumi, Hossein; Regenauer-Lieb, Klaus

2017-01-01

Frictional behaviour of rocks from the initial stage of loading to final shear displacement along the formed shear plane has been widely investigated in the past. However the effect of sample size on such frictional behaviour has not attracted much attention. This is mainly related to the limitations in rock testing facilities as well as the complex mechanisms involved in sample-size dependent frictional behaviour of rocks. In this study, a suite of advanced triaxial experiments was performed on Gosford sandstone samples at different sizes and confining pressures. The post-peak response of the rock along the formed shear plane has been captured for the analysis with particular interest in sample-size dependency. Several important phenomena have been observed from the results of this study: a) the rate of transition from brittleness to ductility in rock is sample-size dependent where the relatively smaller samples showed faster transition toward ductility at any confining pressure; b) the sample size influences the angle of formed shear band and c) the friction coefficient of the formed shear plane is sample-size dependent where the relatively smaller sample exhibits lower friction coefficient compared to larger samples. We interpret our results in terms of a thermodynamics approach in which the frictional properties for finite deformation are viewed as encompassing a multitude of ephemeral slipping surfaces prior to the formation of the through going fracture. The final fracture itself is seen as a result of the self-organisation of a sufficiently large ensemble of micro-slip surfaces and therefore consistent in terms of the theory of thermodynamics. This assumption vindicates the use of classical rock mechanics experiments to constrain failure of pressure sensitive rocks and the future imaging of these micro-slips opens an exciting path for research in rock failure mechanisms.

Increased Rho kinase activity in congestive heart failure

PubMed Central

Dong, Ming; Liao, James K.; Fang, Fang; Lee, Alex Pui-Wai; Yan, Bryan Ping-Yen; Liu, Ming; Yu, Cheuk-Man

2012-01-01

Aims Rho kinases (ROCKs) are the best characterized effectors of the small G-protein RhoA, and play a role in enhanced vasoconstriction in animal models of congestive heart failure (CHF). This study examined if ROCK activity is increased in CHF and how it is associated with the outcome in CHF. Methods and results Patients admitted with CHF (n =178), disease controls (n =31), and normal subjects (n =30) were studied. Baseline ROCK activity was measured by phosphorylation of themyosin-binding subunit in peripheral leucocytes. The patients were followed up for 14.4 ± 7.2 months (range 0.5–26 months) or until the occurrence of cardiac death. The ROCK activity in CHF patients (2.93 ± 0.87) was significantly higher than that of the disease control (2.06 ± 0.38, P < 0.001) and normal control (1.57 ± 0.43, P < 0.001) groups. Similarly, protein levels of ROCK1 and ROCK2 as well as the activity of RhoA in CHF were significantly higher than in disease controls and normal controls (all P < 0.05). Dyspnoea at rest (β =0.338, P < 0.001), low left ventricular ejection fraction (β = –0.277, P < 0.001), and high creatinine (β =0.202, P =0.006) were independent predictors of the baseline ROCK activity in CHF. Forty-five patients died within 2 years follow-up (25.3%). Combining ROCK activity and N-terminal pro brain natriuretic peptide (NT-proBNP) had an incremental value (log rank χ2 =11.62) in predicting long-term mortality when compared with only NT-proBNP (log rank χ2 =5.16, P < 0.05). Conclusion ROCK activity is increased in CHF and it might be associated with the mortality in CHF. ROCK activity might be a complementary biomarker to CHF risk stratification. PMID:22588320

Association of apical rocking with super-response to cardiac resynchronisation therapy.

PubMed

Ghani, A; Delnoy, P P H M; Smit, J J J; Ottervanger, J P; Ramdat Misier, A R; Adiyaman, A; Elvan, A

2016-01-01

Super-responders to cardiac resynchronisation therapy (CRT) show an exceptional improvement in left ventricular ejection fraction (LVEF). Previous studies showed that apical rocking was independently associated with echocardiographic response to CRT. However, little is known about the association between apical rocking and super-response to CRT. To determine the independent association of LV apical rocking with super-response to CRT in a large cohort. A cohort of 297 consecutive heart failure patients treated with primary indication for CRT-D were included in an observational registry. Apical rocking was defined as motion of the left ventricular (LV) apical myocardium perpendicular to the LV long axis. 'Super-response' was defined by the top quartile of LVEF response based on change from baseline to follow-up echocardiogram. Best-subset regression analysis identified predictors of LVEF super-response to CRT. Apical rocking was present in 45 % of patients. Super-responders had an absolute mean LVEF increase of 27 % (LVEF 22.0 % ± 5.7 at baseline and 49.0 % ± 7.5 at follow-up). Apical rocking was significantly more common in super-responders compared with non-super-responders (76 and 34 %, P < 0.001). In univariate analysis, female gender (OR 2.39, 95 % CI 1.38-4.11), lower LVEF at baseline (OR 0.91 95 % CI 0.87-0.95), non-ischaemic aetiology (OR 4.15, 95 % CI 2.33-7.39) and apical rocking (OR 6.19, 95 % CI 3.40-11.25) were associated with super-response. In multivariate analysis, apical rocking was still strongly associated with super-response (OR 5.82, 95 % CI 2.68-12.61). Super-responders showed an excellent clinical prognosis with a very low incidence of heart failure admission, cardiac mortality and appropriate ICD therapy. Apical rocking is independently associated with super-response to CRT.

Why did the 1756 Tjellefonna rockslide occur? A back-analysis of the largest historic rockslide in Norway

NASA Astrophysics Data System (ADS)

Sandøy, Gro; Oppikofer, Thierry; Nilsen, Bjørn

2017-07-01

On 22 February 1756 the largest historically recorded rockslide in Norway took place at Tjelle in the Langfjord (Western Norway). The rockslide created three displacement waves of up to 50 m in height that caused 32 casualties and destroyed most houses and boats along the shores of the Langfjord. The trigger and contributing factors leading to the Tjellefonna rockslide are largely unknown and even seismic triggering has previously been suggested. This study provides a thorough back-analysis of the Tjellefonna rockslide using detailed geomorphological, engineering geological and tectonic field mapping in combination with topographic reconstructions, bathymetry analysis, volume estimations and numerical slope stability analysis. The back-scarp and eastern flank of the Tjellefonna scar form several tens of meter high rock walls, while the basal failure surface and other parts of the scar are covered by rock avalanche debris that extend from the back-scarp down to the bottom of the Langfjord. The rockslide occurred in granodioritic gneisses with variably developed metamorphic foliation that is folded and strike parallel to the fjord. Two prominent fault zones are present in close proximity to the Tjellefonna scar; one is steeply SE-dipping (Tjelle fault), while the other one is sub-horizontal to shallow SE-dipping (Ritlehamran fault). Both fault zones are linked to the Møre-Trøndelag Fault Complex, with one of its branches forming the Langfjord lineament and probably also the faults at Tjellefonna. Additionally, there are four persistent joint sets that together with the metamorphic foliation and the Tjelle fault define the back-scarp of the rockslide and give a fracturing of the rock mass corresponding to a Geological Strength Index (GSI) of 45-55. The GSI decreases significantly to 10-20 in the fault zones, which form distinct weakness zones in the rock slope. Volume estimates based on a reconstruction of the ante-rockslide topography range from 9.3 to 10.4 million m3, which is lower than previous volume estimates (12-15 million m3). Large portions of the failed rock mass remained on land and only approximately 3.9 million m3 entered the fjord. The observed discontinuities in the rock mass at Tjellefonna do not allow for a simple kinematic failure mechanism due to the lack of moderately SE-dipping structures. The basal failure surface was most likely not composed of a single structure, but of a complex interplay of fault zones, metamorphic foliation, joints and broken rock bridges. Numerical slope stability modelling highlights that weak fault zones are essential for the development of the failure surface over a long time. This progressive failure was likely aided by low- to medium-magnitude earthquakes that are frequent in the region. Numerical slope stability modelling and historical accounts suggest, however, that heavy, long-lasting rainfall was the triggering factor for the 1756 Tjellefonna rockslide rather than an earthquake.

Fracturing and Transformation Into Veins Beneath the Crustal Scale Brittle Ductile Transition - a Record of Co-seismic Loading and Post-seismic Relaxation

NASA Astrophysics Data System (ADS)

Nüchter, J. A.; Stöckhert, B.

2005-12-01

Metamorphic rocks approaching the crustal scale brittle-ductile transition (BDT) during exhumation are expected to become increasingly affected by short term stress fluctuations related to seismic activity in the overlying seismogenic layer (schizosphere), while still residing in a long-term viscous environment (plastosphere). The structural and microstructural record of quartz veins in low grade - high pressure metamorphic rocks from southern Evia, Greece, yields insight into the processes and conditions just beneath the long-term BDT at temperatures of about 300 to 350°C, which switches between brittle failure and viscous flow as a function of imposed stress or strain rate. The following features are characteristic: (1) The veins have formed from tensile fractures, with a typical length on the order of 10-1 to 101 m; (2) The veins are discordant with respect to foliation and all pre-existing structures, with a uniform orientation over more than 500 km2; (3) The veins show a low aspect ratio of about 10 to 100 and an irregular or characteristic flame shape, which requires distributed ductile deformation of the host rock; (4) Fabrics of the sealing vein quartz indicate that - at a time - the veins were wide open cavities; (5) The sealing quartz crystals reveal a broad spectrum of microstructural features indicative of crystal plastic deformation at high stress and temperatures of about 300 to 350°C. These features indicate that opening and sealing of the fractures commenced immediately after brittle failure, controlled by ductile deformation of the host rock. Vein-parallel shortening was generally less than about 2%. Crystals formed early during sealing were plastically deformed upon progressive deformation and opening of the vein. The structural and microstructural record is interpreted as follows: Brittle failure is proposed to be a consequence of short term co-seismic loading. Subsequent opening of the fracture and sealing to become a vein is interpreted to reflect the slower (but still very short term on geological time scales) deformation during post-seismic stress relaxation, with precipitation of minerals from the pore fluid percolating into the evolving cavity. The record provides insight into earthquake-related damage in the uppermost plastosphere and the transient crustal properties during post-seismic creep and stress relaxation.

Geological Prediction Ahead of Tunnel Face in the Limestone Formation Tunnel using Multi-Modal Geophysical Surveys

NASA Astrophysics Data System (ADS)

Zaki, N. F. M.; Ismail, M. A. M.; Hazreek Zainal Abidin, Mohd; Madun, Aziman

2018-04-01

Tunnel construction in typical karst topography face the risk which unknown geological condition such as abundant rainwater, ground water and cavities. Construction of tunnel in karst limestone frequently lead to potentially over-break of rock formation and cause failure to affected area. Physical character of limestone which consists large cavity prone to sudden failure and become worsen due to misinterpretation of rock quality by engineer and geologists during analysis stage and improper method adopted in construction stage. Consideration for execution of laboratory and field testing in rock limestone should be well planned and arranged in tunnel construction project. Several tests including Ground Penetration Radar (GPR) and geological face mapping were studied in this research to investigate the performances of limestone rock in tunnel construction, measured in term of rock mass quality that used for risk assessment. The objective of this study is to focus on the prediction of geological condition ahead of tunnel face using short range method (GPR) and verified by geological face mapping method to determine the consistency of actual geological condition on site. Q-Value as the main indicator for rock mass classification was obtained from geological face mapping method. The scope of this study is covering for tunnelling construction along 756 meters in karst limestone area which located at Timah Tasoh Tunnel, Bukit Tebing Tinggi, Perlis. For this case study, 15% of GPR results was identified as inaccurate for rock mass classification in which certain chainage along this tunnel with 34 out of 224 data from GPR was identified as incompatible with actual face mapping.

The role of strain hardening in the transition from dislocation-mediated to frictional deformation of marbles within the Karakoram Fault Zone, NW India

NASA Astrophysics Data System (ADS)

Wallis, David; Lloyd, Geoffrey E.; Hansen, Lars N.

2018-02-01

The onset of frictional failure and potentially seismogenic deformation in carbonate rocks undergoing exhumation within fault zones depends on hardening processes that reduce the efficiency of aseismic dislocation-mediated deformation as temperature decreases. However, few techniques are available for quantitative analysis of dislocation slip system activity and hardening in natural tectonites. Electron backscatter diffraction maps of crystal orientations offer one such approach via determination of Schmid factors, if the palaeostress conditions can be inferred and the critical resolved shear stresses of slip systems are constrained. We analyse calcite marbles deformed in simple shear within the Karakoram Fault Zone, NW India, to quantify changes in slip system activity as the rocks cooled during exhumation. Microstructural evidence demonstrates that between ∼300 °C and 200-250 °C the dominant deformation mechanisms transitioned from dislocation-mediated flow to twinning and frictional failure. However, Schmid factor analysis, considering critical resolved shear stresses for yield of undeformed single crystals, indicates that the fraction of grains with sufficient resolved shear stress for glide apparently increased with decreasing temperature. Misorientation analysis and previous experimental data indicate that strain-dependent work hardening is responsible for this apparent inconsistency and promoted the transition from dislocation-mediated flow to frictional, and potentially seismogenic, deformation.

Support design and practice for floor heave of deeply buried roadway

NASA Astrophysics Data System (ADS)

Liu, Chaoke; Ren, Jianxi; Gao, Bingli; Song, Yongjun

2017-05-01

Aiming at the severe floor heave of auxiliary haulage roadway in Jianzhuang Coal Mine, the paper analysed mechanical environment and failure characteristics of auxiliary haulage roadway surrounding rock with the combination of mechanical test, theoretical analysis, industrial test, etc. The mechanical mechanism for deformation and failure of weak rock roadway in Jianzhuang Coal Mine was disclosed by establishing a roadway mechanical model under the effect of even-distributed load, which provided a basis for the design of inverted concrete arch. Based on complex failure mechanism of the roadway, a support method with combined inverted concrete arch and anchor in floor was proposed. The result shows that the ground stress environment has extremely adverse influence on the roadway, and the practice indicates that the floor heave countermeasures can effectively control the floor heave. The obtained conclusion provides a reference for the research and design on control technology of roadway floor heave in the future.

Subsidence and well failure in the South Belridge Diatomite field

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rouffignac, E.P. de; Bondor, P.L.; Karanikas, J.M. Hara, S.K.

1995-12-31

Withdrawal of fluids from shallow, thick and low strength rock can cause substantial reservoir compaction leading to surface subsidence and well failure. This is the case for the Diatomite reservoir, where over 10 ft of subsidence have occurred in some areas. Well failure rates have averaged over 3% per year, resulting in several million dollars per year in well replacement and repair costs in the South Belridge Diatomite alone. A program has been underway to address this issue, including experimental, modeling and field monitoring work. An updated elastoplastic rock law based on laboratory data has been generated which includes notmore » only standard shear failure mechanisms but also irreversible pore collapse occurring at low effective stresses (<150 psi). This law was incorporated into a commercial finite element geomechanics simulator. Since the late 1980s, a network of level survey monuments has been used to monitor subsidence at Belridge. Model predictions of subsidence in Section 33 compare very well with field measured data, which show that water injection reduces subsidence from 7--8 inches per year to 1--2 inches per year, but does not abate well failure.« less

Rock burst governance of working face under igneous rock

NASA Astrophysics Data System (ADS)

Chang, Zhenxing; Yu, Yue

2017-01-01

As a typical failure phenomenon, rock burst occurs in many mines. It can not only cause the working face to cease production, but also cause serious damage to production equipment, and even result in casualties. To explore how to govern rock burst of working face under igneous rock, the 10416 working face in some mine is taken as engineering background. The supports damaged extensively and rock burst took place when the working face advanced. This paper establishes the mechanical model and conducts theoretical analysis and calculation to predict the fracture and migration mechanism and energy release of the thick hard igneous rock above the working face, and to obtain the advancing distance of the working face when the igneous rock fractures and critical value of the energy when rock burst occurs. Based on the specific conditions of the mine, this paper put forward three kinds of governance measures, which are borehole pressure relief, coal seam water injection and blasting pressure relief.

Fault Damage Zone Permeability in Crystalline Rocks from Combined Field and Laboratory Measurements: Can we Predict Damage Zone Permeability?

NASA Astrophysics Data System (ADS)

Mitchell, T. M.; Faulkner, D. R.

2009-04-01

Models predicting crustal fluid flow are important for a variety of reasons; for example earthquake models invoking fluid triggering, predicting crustal strength modelling flow surrounding deep waste repositories or the recovery of natural resources. Crustal fluid flow is controlled by both the bulk transport properties of rocks as well as heterogeneities such as faults. In nature, permeability is enhanced in the damage zone of faults, where fracturing occurs on a wide range of scales. Here we analyze the contribution of microfracture damage on the permeability of faults that cut through low porosity, crystalline rocks by combining field and laboratory measurements. Microfracture densities surrounding strike-slip faults with well-constrained displacements ranging over 3 orders of magnitude (~0.12 m - 5000 m) have been analyzed. The faults studied are excellently exposed within the Atacama Fault Zone, where exhumation from 6-10 km has occurred. Microfractures in the form of fluid inclusion planes (FIPs) show a log-linear decrease in fracture density with perpendicular distance from the fault core. Damage zone widths defined by the density of FIPs scale with fault displacement, and an empirical relationship for microfracture density distribution throughout the damage zone with displacement is derived. Damage zone rocks will have experienced differential stresses that were less than, but some proportion of, the failure stress. As such, permeability data from progressively loaded, initially intact laboratory samples, in the pre-failure region provide useful insights into fluid flow properties of various parts of the damage zone. The permeability evolution of initially intact crystalline rocks under increasing differential load leading to macroscopic failure was determined at water pore pressures of 50 MPa and effective pressure of 10 MPa. Permeability is seen to increase by up to, and over, two orders of magnitude prior to macroscopic failure. Further experiments were stopped at various points in the loading history in order to correlate microfracture density within the samples with permeability. By combining empirical relationships determined from both quantitative fieldwork and experiments we present a new model that allows microfracture permeability distribution throughout the damage zone to be determined as function of increasing fault displacement.

A three-dimensional back-analysis of the collapse of an underground cavity in soft rocks

NASA Astrophysics Data System (ADS)

Fazio, Nunzio Luciano; Lollino, Piernicola; Perrotti, Michele; Parise, Mario; Bonamini, Marco; Di Maggio, Cipriano; Madonia, Giuliana; Vattano, Marco

2016-04-01

Anthropogenic sinkholes have recently occurred in built-up areas of Sicily (southern Italy) and are generally associated with the presence of ancient underground quarries for the extraction of soft calcarenite rock, used as building material. These quarries were poorly excavated and then were abandoned in the following decades; urban expansion has recently enlarged to involve the areas affected by presence of the cavities, so that the likely collapse of the underground systems poses serious risks to people, buildings and infrastructures. The present work focuses on the case of the town of Marsala, where in 2003 a sinkhole opened at the outskirts of town, near peri-urban buildings. Field surveys, structural analysis of the joint networks in the rock mass and numerical modeling were carried out in order to investigate the most significant factors responsible of the instability processes of the underground quarry. In particular, a geotechnical three-dimensional model has been defined based on in-situ measurements and surveys. The FEM analyses have been performed with the code Plaxis-3D, by using initially the Mohr-Coulomb elasto-plastic model and then assessing the influence of the joint systems on the rock-mass stability with a jointed rock anisotropic model. Discrete planar bands have been also used to simulate the effect of specific joints, as an alternative to the jointed rock model. The results are in good agreement with the failure mechanism generated during the 2003 sinkhole event, and confirm that reliable analyses of these problems requires 3-D sophisticated tools.

Brittle and Ductile Behavior in Deep-Seated Landslides: Learning from the Vajont Experience

NASA Astrophysics Data System (ADS)

Paronuzzi, Paolo; Bolla, Alberto; Rigo, Elia

2016-06-01

This paper analyzes the mechanical behavior of the unstable Mt. Toc slope before the 1963 catastrophic collapse, considering both the measured data (surface displacements and microseismicity) and the updated geological model of the prehistoric rockslide. From February 1960 up to 9 October 1963, the unstable mass behaved as a brittle-ductile `mechanical system,' characterized by remarkable microseismicity as well as by considerable surface displacements (up to 4-5 m). Recorded microshocks were the result of progressive rock fracturing of distinct resisting stiff parts made up of intact rock (indentations, undulations, and rock bridges). The main resisting stiff part was a large rock indentation located at the NE extremity of the unstable mass that acted as a mechanical constraint during the whole 1960-1963 period, inducing a progressive rototranslation toward the NE. This large constraint failed in autumn 1960, when an overall slope failure took place, as emphasized by the occurrence of the large perimetrical crack in the upper slope. In this circumstance, the collapse was inhibited by a reblocking phenomenon of the unstable mass that had been previously destabilized by the first reservoir filling. Progressive failure of localized intact rock parts progressively propagated westwards as a consequence of the two further filling-drawdown cycles of the reservoir (1962 and 1963). The characteristic brittle-ductile behavior of the Vajont landslide was made possible by the presence of a very thick (40-50 m) and highly deformable shear zone underlying the upper rigid rock mass (100-120 m thick).

Ground-based LiDAR application to characterize sea cliff instability processes along a densely populated coastline in Southern Italy

NASA Astrophysics Data System (ADS)

Esposito, Giuseppe; Semaan, Fouad; Salvini, Riccardo; Troise, Claudia; Somma, Renato; Matano, Fabio; Sacchi, Marco

2017-04-01

Sea cliff retreatment along the coastline of the Campi Flegrei volcanic area (Southern Italy) is becoming a threat for public and private structures due to the massive urbanization occurred in the last few decades. In this area, geological features of the outcropping rocks represent one of the most important factors conditioning the sea cliff retreatment. In fact, pyroclastic deposits formed by pumices, scoria, ashes and lapilli are arranged in weakly to moderately welded layers of variable thicknesses, resulting very erodible and prone to landslide processes. Available methods to evaluate topographic changes and retreat rates of sea cliffs include a variety of geomatic techniques, like terrestrial and aerial photogrammetry and LiDAR (Light Detection And Ranging). By means of such techniques, it is in fact possible to obtain high resolution topography of sea cliffs and perform multi-temporal change detection analysis. In this contribution, we present an application of Terrestrial Laser Scanning (TLS or ground-based LiDAR) aimed to identify and quantify instability processes acting along the Torrefumo coastal cliff, in the Campi Flegrei area. Specifically, we acquired a series of 3D point clouds on the years 2013 and 2016, and compared them through a cloud-to-cloud distance computation. Furthermore, a statistical analysis was applied to the change detection results. In this way, an inventory of the cliff failures occurred along the Torrefumo cliff in the 2013-2016 time span was created, as well as the spatial and volumetric distribution of these failures was evaluated. The volumetric analysis shows that large collapses occurred rarely, whereas the spatial analysis shows that the majority of failures occurred in the middle and upper parts of the cliff face. Results also show that both rock fall and surficial erosion processes contribute to the cliff retreatment, acting in turn according to the geological properties of the involved pyroclastic deposits. The presented TLS approach proves to be a cost and time efficient method for characterizing the geomorphic changes involving the sea cliff surfaces over a short-time period (i.e. monthly or yearly). The accuracy of the acquired data allows the characterization of a full range of failures to be located and quantified with a level of detail not reachable using traditional techniques. Results obtained in this research will be used in future applications to assess hazard conditions affecting the anthropic structures built close to the cliff top.

Failure warning of hydrous sandstone based on electroencephalogram technique

NASA Astrophysics Data System (ADS)

Tao, Kai; Zheng, Wei

2018-06-01

Sandstone is a type of rock mass that widely exists in nature. Moisture is an important factor that leads to sandstone structural failure. The major failure assessment methods of hydrous sandstone at present cannot satisfy real-time and portability requirements, especially lacks of warning function. In this study, acoustic emission (AE) and computed tomography (CT) techniques are combined for real-time failure assessment of hydrous sandstone. Eight visual colors for warning are screened according to different failure states, and an electroencephalogram (EEG) experiment is conducted to demonstrate their diverse excitations of the human brain's concentration.

The application of continuum damage mechanics to solve problems in geodynamics

NASA Astrophysics Data System (ADS)

Manaker, David Martin

Deformation within the Earth's lithosphere is largely controlled by the rheology of the rock. Ductile behavior in rocks is often associated with plasticity due to dislocation motion or diffusion under high pressures and temperatures. However, ductile behavior can also occur in brittle materials. An example would be cataclastic flow associated with folding at shallow crustal levels, steep subduction zones, and large-scale deformation at plate boundaries. Engineers utilize damage mechanics to model the continuum deformation of brittle materials. We utilize a modified form of damage mechanics where damage represents a reduction in frictional strength and includes a yield stress. We use this empirical approach to simulate the bending of the lithosphere. We use numerical simulations to obtain elastostatic solutions for plate bending and where the stress exceeds a yield stress, we apply damage to reduce the elastic moduli. Damage is calculated at each time step by a power-law relationship of the ratio of the yield stress to stress and the yield strain to the strain. To test our method, we apply our damage rheology to a plate deforming under applied shear, a constant bending moment, and a constant load. We simulate a wide range of behaviors from slow relaxation to instantaneous failure, over timescales that span six orders of magnitude. Stress relaxation produces elastic-perfectly plastic behavior in cases where failure does not occur. For cases of failure, we observe a rapid increase in damage leading to failure. The changes in the rate of damage accumulation in failure cases are similar to the changes in b-values of acoustic emissions observed in triaxial compression tests of fractured rock and b-value changes prior to some large earthquakes. Thus continuum damage mechanics can simulate ductile behavior due to brittle mechanisms as well as observations of laboratory experiments and seismicity.

A Review of Rock Bolt Monitoring Using Smart Sensors.

PubMed

Song, Gangbing; Li, Weijie; Wang, Bo; Ho, Siu Chun Michael

2017-04-05

Rock bolts have been widely used as rock reinforcing members in underground coal mine roadways and tunnels. Failures of rock bolts occur as a result of overloading, corrosion, seismic burst and bad grouting, leading to catastrophic economic and personnel losses. Monitoring the health condition of the rock bolts plays an important role in ensuring the safe operation of underground mines. This work presents a brief introduction on the types of rock bolts followed by a comprehensive review of rock bolt monitoring using smart sensors. Smart sensors that are used to assess rock bolt integrity are reviewed to provide a firm perception of the application of smart sensors for enhanced performance and reliability of rock bolts. The most widely used smart sensors for rock bolt monitoring are the piezoelectric sensors and the fiber optic sensors. The methodologies and principles of these smart sensors are reviewed from the point of view of rock bolt integrity monitoring. The applications of smart sensors in monitoring the critical status of rock bolts, such as the axial force, corrosion occurrence, grout quality and resin delamination, are highlighted. In addition, several prototypes or commercially available smart rock bolt devices are also introduced.

Applicability of geomechanical classifications for estimation of strength properties in Brazilian rock masses.

PubMed

Santos, Tatiana B; Lana, Milene S; Santos, Allan E M; Silveira, Larissa R C

2017-01-01

Many authors have been proposed several correlation equations between geomechanical classifications and strength parameters. However, these correlation equations have been based in rock masses with different characteristics when compared to Brazilian rock masses. This paper aims to study the applicability of the geomechanical classifications to obtain strength parameters of three Brazilian rock masses. Four classification systems have been used; the Rock Mass Rating (RMR), the Rock Mass Quality (Q), the Geological Strength Index (GSI) and the Rock Mass Index (RMi). A strong rock mass and two soft rock masses with different degrees of weathering located in the cities of Ouro Preto and Mariana, Brazil; were selected for the study. Correlation equations were used to estimate the strength properties of these rock masses. However, such correlations do not always provide compatible results with the rock mass behavior. For the calibration of the strength values obtained through the use of classification systems, ​​stability analyses of failures in these rock masses have been done. After calibration of these parameters, the applicability of the various correlation equations found in the literature have been discussed. According to the results presented in this paper, some of these equations are not suitable for the studied rock masses.

A Review of Rock Bolt Monitoring Using Smart Sensors

PubMed Central

Song, Gangbing; Li, Weijie; Wang, Bo; Ho, Siu Chun Michael

2017-01-01

Rock bolts have been widely used as rock reinforcing members in underground coal mine roadways and tunnels. Failures of rock bolts occur as a result of overloading, corrosion, seismic burst and bad grouting, leading to catastrophic economic and personnel losses. Monitoring the health condition of the rock bolts plays an important role in ensuring the safe operation of underground mines. This work presents a brief introduction on the types of rock bolts followed by a comprehensive review of rock bolt monitoring using smart sensors. Smart sensors that are used to assess rock bolt integrity are reviewed to provide a firm perception of the application of smart sensors for enhanced performance and reliability of rock bolts. The most widely used smart sensors for rock bolt monitoring are the piezoelectric sensors and the fiber optic sensors. The methodologies and principles of these smart sensors are reviewed from the point of view of rock bolt integrity monitoring. The applications of smart sensors in monitoring the critical status of rock bolts, such as the axial force, corrosion occurrence, grout quality and resin delamination, are highlighted. In addition, several prototypes or commercially available smart rock bolt devices are also introduced. PMID:28379167

Experimental study on deformation field evolution in rock sample with en echelon faults using digital speckle correlation method

NASA Astrophysics Data System (ADS)

Ma, S.; Ma, J.; Liu, L.; Liu, P.

2007-12-01

Digital speckle correlation method (DSCM) is one kind of photomechanical deformation measurement method. DSCM could obtain continuous deformation field contactlessly by just capturing speckle images from specimen surface. Therefore, it is suitable to observe high spatial resolution deformation field in tectonophysical experiment. However, in the general DSCM experiment, the inspected surface of specimen needs to be painted to bear speckle grains in order to obtain the high quality speckle image. This also affects the realization of other measurement techniques. In this study, an improved DSCM system is developed and utilized to measure deformation field of rock specimen without surface painting. The granodiorite with high contrast nature grains is chosen to manufacture the specimen, and a specially designed DSCM algorithm is developed to analyze this kind of nature speckle images. Verification and calibration experiments show that the system could inspect a continuous (about 15Hz) high resolution displacement field (with resolution of 5μm) and strain field (with resolution of 50μɛ), dispensing with any preparation on rock specimen. Therefore, it could be conveniently utilized to study the failure of rock structure. Samples with compressive en echelon faults and extensional en echelon faults are studied on a two-direction servo-control test machine. The failure process of the samples is discussed based on the DSCM results. Experiment results show that: 1) The contours of displacement field could clearly indicate the activities of faults and new cracks. The displacement gradient adjacent to active faults and cracks is much greater than other areas. 2) Before failure of the samples, the mean strain of the jog area is largest for the compressive en echelon fault, while that is smallest for the extensional en echelon fault. This consists with the understanding that the jog area of compressive fault subjects to compression and that of extensional fault subjects to tension. 3) For the extensional en echelon sample, the dislocation across fault on load-driving end is greater than that cross fault on fixed end. Within the same fault, the dislocation across branch far from the jog area is greater than that across branch near the jog area. This indicates the restriction effect of jog area on the activity of fault. Moreover, the average dislocation across faults is much greater than that across the cracks. 4) For the compressive en echelon fault, the wing cracks initialized firstly and propagate outwards the jog area. Subsequently, a wedge strain concentration area is initialized and developed in the jog area because of the interaction of the two faults. Finally, the jog area failed when one crack propagates rapidly and connects the two ends of faults. The DSCM system used in this study could clearly show the deformation and failure process of the en echelon fault sample. The experiment using DSCM could be performed dispensing with any preparation on specimen and not affecting other inspection. Therefore, DSCM is expected to be a suitable tool for experimental study of fault samples in laboratory.

A relation to describe rate-dependent material failure.

PubMed

Voight, B

1989-01-13

The simple relation OmegaOmega-alpha = 0, where Omega is a measurable quantity such as strain and A and alpha are empirical constants, describes the behavior of materials in terminal stages of failure under conditions of approximately constant stress and temperature. Applicable to metals and alloys, ice, concrete, polymers, rock, and soil, the relation may be extended to conditions of variable and multiaxial stress and may be used to predict time to failure.

Developing a shale heterogeneity index to predict fracture response in the Mancos Shale

NASA Astrophysics Data System (ADS)

DeReuil, Aubry; Birgenheier, Lauren; McLennan, John

2017-04-01

The interplay between sedimentary heterogeneity and fracture propagation in mudstone is crucial to assess the potential of low permeability rocks as unconventional reservoirs. Previous experimental research has demonstrated a relationship between heterogeneity and fracture of brittle rocks, as discontinuities in a rock mass influence micromechanical processes such as microcracking and strain localization, which evolve into macroscopic fractures. Though numerous studies have observed heterogeneity influencing fracture development, fundamental understanding of the entire fracture process and the physical controls on this process is still lacking. This is partly due to difficulties in quantifying heterogeneity in fine-grained rocks. Our study tests the hypothesis that there is a correlation between sedimentary heterogeneity and the manner in which mudstone is fractured. An extensive range of heterogeneity related to complex sedimentology is represented by various samples from cored intervals of the Mancos Shale. Samples were categorized via facies analysis consisting of: visual core description, XRF and XRD analysis, SEM and thin section microscopy, and reservoir quality analysis that tested porosity, permeability, water saturation, and TOC. Systematic indirect tensile testing on a broad variety of facies has been performed, and uniaxial and triaxial compression testing is underway. A novel tool based on analytically derived and statistically proven relationships between sedimentary geologic and geomechanical heterogeneity is the ultimate result, referred to as the shale heterogeneity index. Preliminary conclusions from development of the shale heterogeneity index reveal that samples with compositionally distinct bedding withstand loading at higher stress values, while texturally and compositionally homogeneous, bedded samples fail at lower stress values. The highest tensile strength results from cemented Ca-enriched samples, medial to high strength samples have approximately equivalent proportions of Al-Ca-Si compositions, while Al-rich samples have consistently low strength. Moisture preserved samples fail on average at approximately 5 MPa lower than dry samples of similar facies. Additionally, moisture preserved samples fail in a step-like pattern when tested perpendicular to bedding. Tensile fractures are halted at heterogeneities and propagate parallel to bedding planes before developing a through-going failure plane, as opposed to the discrete, continuous fractures that crosscut dry samples. This result suggests that sedimentary heterogeneity plays a greater role in fracture propagation in moisture preserved samples, which are more indicative of in-situ reservoir conditions. Stress-strain curves will be further analyzed, including estimation of an energy released term based on post-failure response, and an estimation of volume of cracking measure on the physical fracture surface.

Microseismicity of an Unstable Rock Mass: From Field Monitoring to Laboratory Testing

NASA Astrophysics Data System (ADS)

Colombero, C.; Comina, C.; Vinciguerra, S.; Benson, P. M.

2018-02-01

The field-scale microseismic (MS) activity of an unstable rock mass is known to be an important tool to assess damage and cracking processes eventually leading to macroscopic failures. However, MS-event rates alone may not be enough for a complete understanding of the trigger mechanisms of mechanical instabilities. Acoustic Emission (AE) techniques at the laboratory scale can be used to provide complementary information. In this study, we report a MS/AE comparison to assess the stability of a granitic rock mass in the northwestern Italian Alps (Madonna del Sasso). An attempt to bridge the gap between the two different scales of observation, and the different site and laboratory conditions, is undertaken to gain insights on the rock mass behavior as a function of external governing factors. Time- and frequency-domain parameters of the MS/AE waveforms are compared and discussed with this aim. At the field scale, special attention is devoted to the correlation of the MS-event rate with meteorological parameters (air temperature and rainfalls). At the laboratory scale, AE rates, waveforms, and spectral content, recorded under controlled temperature and fluid conditions, are analyzed in order to better constrain the physical mechanisms responsible for the observed field patterns. The factors potentially governing the mechanical instability at the site were retrieved from the integration of the results. Abrupt thermal variations were identified as the main cause of the site microsesimicity, without highlighting irreversible acceleration in the MS-event rate potentially anticipating the rock mass collapse.

Back-analysis of a large landslide in a heterogeneous rock mass

NASA Astrophysics Data System (ADS)

Berti, Matteo; Gamba, Alberto; Pizziolo, Marco

2014-05-01

On April 6, 2013 a large landslide occurred on the mountainside about 2 km above Castel dell'Alpi, a small community located on the Savena River valley (Province of Bologna, Northern Apennines, Italy). Three houses collapsed, two were seriously damaged, and the existing roads and infrastructures were destroyed. The landslide was a massive rotational slide about 900 m long, 600 m wide and covering an area of 0.3 km2. The estimated volume was about 3 million cubic meters. According to eyewitnesses, diffuse ground deformations appeared in the morning of April 6 along the road that runs at the toe of the slope, and became more and more prominent during the afternoon. The landslide suddenly accelerated during the night and moved downslope 50 to 100 m in a few hours. Fortunately, residents were alerted by the sound of cracking wood and left their houses in time, thus resulted in no fatalities or injuries. The landslide created a large, bowl-shaped scar with a steep scarp about 70 m height and 800 m long. The head of the landslide moved almost vertically downward and tilted backwards, while ground bulging and compressive structures occurred at the toe. These kinematic features indicate a strong rotational component of the slide, although the high degree of internal deformation suggests a non-perfectly circular slip surface. It is well known that rotational slides tend to occur in deep homogeneous material such as thick clay soils, weak rocks, or artificial fills. In this case, however, the failure involved a strongly heterogeneous flysch, apparently characterized by good mechanical resistance. The rock belongs to the Monghidoro Formation (Cretaceous sup.-Paleocene) and consists of thinly interbedded sandstone, marl, and shale. The rock mass outcropping on the main scarp is only slight to moderately weathered, with nearly-horizontal bedding planes. Therefore, failure conditions were probably reached within the "fresh" material and, despite its heterogeneity, the flysch behaved as an homogeneous medium at the slope scale. Such a behavior is typical of this rock. A number of old rotational slides can be found in the area, and they all show the morphological features (such as a steep arcuate scarp with exposed bedrock and sub-circular landslide deposit) that characterize rotational failures in homogeneous materials. The landslide of April 2013 thus provides the opportunity to investigate in depth the mechanical behavior of this complex formation. The analysis mainly focused on the evaluation of the mobilized shear strength at failure. The slope geometry before the failure was reconstructed by combining the pre-failure 5 m DEM, the post-failure 1 m DEM (LIDAR) and the kinematic interpretation of the geomorphological features. Mobilised shear strength parameters were compute by limit-equilibrium and finite-difference back-analyses, considering a wide variation of groundwater head levels, initial stress state, and slip surface depth. The results clearly indicate that the flysch is characterized by low mass strength and small effective cohesion (in the order of few tens of kPa). The mobilized cohesion is much lower than that predicted by the geomechanical classification of heterogeneous rock masses, and casts doubts on the reliability of such estimates for the prediction of large slope instability.

Thermal Effect on Fracture Integrity in Enhanced Geothermal Systems

NASA Astrophysics Data System (ADS)

Zeng, C.; Deng, W.; Wu, C.; Insall, M.

2017-12-01

In enhanced geothermal systems (EGS), cold fluid is injected to be heated up for electricity generation purpose, and pre-existing fractures are the major conduits for fluid transport. Due to the relative cold fluid injection, the rock-fluid temperature difference will induce thermal stress along the fracture wall. Such large thermal stress could cause the failure of self-propping asperities and therefore change the fracture integrity, which could affect the heat recovery efficiency and fluid recycling. To study the thermal effect on fracture integrity, two mechanisms pertinent to thermal stress are proposed to cause asperity contact failure: (1) the crushing between two pairing asperities leads to the failure at contact area, and (2) the thermal spalling expedites this process. Finite element modeling is utilized to investigate both failure mechanisms by idealizing the asperities as hemispheres. In the numerical analysis, we have implemented meso-scale damage model to investigate coupled failure mechanism induced by thermomechanical stress field and original overburden pressure at the vicinity of contact point. Our results have shown that both the overburden pressure and a critical temperature determine the threshold of asperity failure. Since the overburden pressure implies the depth of fractures in EGS and the critical temperature implies the distance of fractures to the injection well, our ultimate goal is to locate a region of EGS where the fracture integrity is vulnerable to such thermal effect and estimate the influences.

Anomalous concentrations of seismically triggered rock falls in Pacoima Canyon: Are they caused by highly susceptible slopes or local amplification of seismic shaking?

USGS Publications Warehouse

Harp, Edwin L.; Jibson, Randall W.

2002-01-01

Anomalously high concentrations of rock falls were triggered in Pacoima Canyon (Los Angeles, California) during the 1994 Northridge earthquake. Similar concentrations were also documented from the 1971 San Fernando earthquake. Using an engineering rock-mass classification that evaluates the susceptibility of rock slopes to seismic failure based on the fracture properties of a rock mass (in terms of a numerical "Q-value" that describes rock quality), the rock slopes in Pacoima Canyon were compared with rock slopes in sorrounding areas where topography and lithology are similar, but rock-fall concentrations from the earthquakes were much lower. A statistical comparison of Q-values from five sites surrounding Pacoima Canyon indicates that seismic susceptibilities are similar to those within Pacoima Canyon; differences in the characteristics of rock slopes between these sites are not sufficient to account for the relatively high concentrations of rock falls within Pacoima Canyon as compared to low concentrations elsewhere. By eliminating susceptibility differences as a cause, the most likely explanations for the differences in rock-fall concentrations is anomalously high shaking levels in Pacoima Canyon, possibly resulting from topographic amplification within the canyon.

Ductile creep and compaction: A mechanism for transiently increasing fluid pressure in mostly sealed fault zones

USGS Publications Warehouse

Sleep, Norman H.; Blanpied, M.L.

1994-01-01

A simple cyclic process is proposed to explain why major strike-slip fault zones, including the San Andreas, are weak. Field and laboratory studies suggest that the fluid within fault zones is often mostly sealed from that in the surrounding country rock. Ductile creep driven by the difference between fluid pressure and lithostatic pressure within a fault zone leads to compaction that increases fluid pressure. The increased fluid pressure allows frictional failure in earthquakes at shear tractions far below those required when fluid pressure is hydrostatic. The frictional slip associated with earthquakes creates porosity in the fault zone. The cycle adjusts so that no net porosity is created (if the fault zone remains constant width). The fluid pressure within the fault zone reaches long-term dynamic equilibrium with the (hydrostatic) pressure in the country rock. One-dimensional models of this process lead to repeatable and predictable earthquake cycles. However, even modest complexity, such as two parallel fault splays with different pressure histories, will lead to complicated earthquake cycles. Two-dimensional calculations allowed computation of stress and fluid pressure as a function of depth but had complicated behavior with the unacceptable feature that numerical nodes failed one at a time rather than in large earthquakes. A possible way to remove this unphysical feature from the models would be to include a failure law in which the coefficient of friction increases at first with frictional slip, stabilizing the fault, and then decreases with further slip, destabilizing it. ?? 1994 Birkha??user Verlag.

Friction of hard surfaces and its application in earthquakes and rock slope stability

NASA Astrophysics Data System (ADS)

Sinha, Nitish; Singh, Arun K.; Singh, Trilok N.

2018-05-01

In this article, we discuss the friction models for hard surfaces and their applications in earth sciences. The rate and state friction (RSF) model, which is basically modified form of the classical Amontons-Coulomb friction laws, is widely used for explaining the crustal earthquakes and the rock slope failures. Yet the RSF model has further been modified by considering the role of temperature at the sliding interface known as the rate, state and temperature friction (RSTF) model. Further, if the pore pressure is also taken into account then it is stated as the rate, state, temperature and pore pressure friction (RSTPF) model. All the RSF models predict a critical stiffness as well as a critical velocity at which sliding behavior becomes stable/unstable. The friction models are also used for predicting time of failure of the rock mass on an inclined plane. Finally, the limitation and possibilities of the proposed friction models are also highlighted.

The influence of temperature on brittle creep in sandstones

NASA Astrophysics Data System (ADS)

Heap, M. J.; Baud, P.; Meredith, P. G.; Vinciguerra, S.

2009-04-01

The characterization of time-dependent brittle rock deformation is fundamental to understanding the long-term evolution and dynamics of the Earth's upper crust. The presence of water promotes time-dependent deformation through environment-dependent stress corrosion cracking that allows rocks to deform at stresses far below their short-term failure stress. Here we report results from an experimental study of the influence of an elevated temperature on time-dependent brittle creep in water-saturated samples of Darley Dale (initial porosity of 13%), Bentheim (23%) and Crab Orchard (4%) sandstones. We present results from both conventional creep experiments (or ‘static fatigue' tests) and stress-stepping creep experiments performed under 20°C and 75°C and an effective confining pressure of 30 MPa (50 MPa confining pressure and a 20 MPa pore fluid pressure). The evolution of crack damage was monitored throughout each experiment by measuring the three proxies for damage (1) axial strain (2) pore volume change and (3) the output of AE energy. Conventional creep experiments have demonstrated that, for any given applied differential stress, the time-to-failure is dramatically reduced and the creep strain rate is significantly increased by application of an elevated temperature. Stress-stepping creep experiments have allowed us to investigate the influence of temperature in detail. Results from these experiments show that the creep strain rate for Darley Dale and Bentheim sandstones increases by approximately 3 orders of magnitude, and for Crab Orchard sandstone increases by approximately 2 orders of magnitude, as temperature is increased from 20°C to 75°C at a fixed effective differential stress. We discuss these results in the context of the different mineralogical and microstructural properties of the three rock types and the micro-mechanical and chemical processes operating on them.

Deformation and stabilisation mechanisms of slow rock slides in crystalline bedrock

NASA Astrophysics Data System (ADS)

Zangerl, C.; Prager, C.

2009-04-01

Deep-seated rock slides are slope instabilities which are characterised by deformation along one or several shear zones where most of the measured total slope displacement localizes. Generally, a high danger potential is given when rock slides fail in a rapid manner characterised by very high sliding velocities and/or when they develop into long run-out rock avalanches. However several field surveys and deformation monitoring data show that numerous deep-seated rock slides do not fail in a high velocity regime. In fact, many slides creep downwards at rates of some centimetres per year or even less and do not show any evidence for non-reversible acceleration in the past or in the future. Furthermore some of these slope instabilities are actually inactive (dormant) or have even reached a stabilised final state. Deformation monitoring on active rock slides show that acceleration phases characterised by velocities up to meters per day can occur. The trigger for these phases can be manifold and include heavy rainfall, snow melt, water level fluctuations of reservoirs at the slope foot, changes in the slope's equilibrium state due to antecedent slow creeping processes, changes in the material behaviour within the sliding zone, erosion along the foot of the slope, etc. Whereas the role of these triggers in promoting phases of acceleration are generally understood, the same can not be said regarding the kinematics and dynamic processes/mechanisms by which rock slide masses re-stabilise once the trigger impetus has been removed. In the context of this study the term "stabilisation" is used for rock slides which decelerate from high velocities to slow base activities or even stop moving after a certain amount of displacement. Given that reliable rock slide forecasts require the fundamental understanding of possible slope stabilisation mechanisms this study focuses on field-based and numerically obtained key-properties which influence the long-term slope deformation behaviour. On a regional scale several valleys located in amphibolites, ortho- and paragneisses of the Ötztal-Stubai crystalline basement (i.e. Kaunertal, Pitztal, Ötztal, Lüsenstal, all located in North Tyrol, Austria) were investigated. Therefore geological and morphological basis data were compiled and re-evaluated, remote sensing methods (i.e. airborne laser scanning terrain models and orthofotos) applied and field mapping campaigns performed. On a local scale several rock slides were investigated and analysed in high detail with regard to their lithological and structural inventory, geometry of sliding masses and -zones, failure mechanisms, kinematics and temporal deformation characteristics. Field data clearly show that competent rock masses, e.g. orthogneisses and amphibolites, are affected by rapid failure events and therefore are characterised by "brittle" rock mass behaviour. In contrast, the majority of the slowly moving and "self-stabilising" rock slides are located totally or partly in mica-rich incompetent crystalline rock masses, e.g. paragneisses and micaschists, and are characterised by moderately dipping sliding zones. Apart from a causal lithological influence, numerous field observations demonstrate a major influence of pre-existing geological structures on the formation and deformation behaviour of these rock slides. The nature of rock slides implies that the temporal deformation behaviour is primarily dominated by two key-features of the sliding zone i.e. the mechanical properties (shear strain strengthening or weakening) and the effective in-situ stresses. The in-situ stresses along a sliding zone are influenced by the geometry of both the sliding mass and sliding zone, the internal deformation of the sliding mass and the pore pressures. All these properties can vary during progressive shear displacements. Especially large shear displacements in the range of tens to hundreds of metres along a distinct sliding zone can cause significant in-situ stress changes which in turn may influence the slope deformation behaviour and stabilisation mechanisms. In order to study these processes for selected case studies in paragneissic rock masses the impact of the sliding mass geometry and sliding zone shape on the in-situ stresses has been investigated by applying the discrete element method. This numerical approach enables the simulation of large shear displacements and complex block assembly interactions. Results show that slope stabilisation can be achieved when the dip angle of the sliding zone flattens downslope. In this case and after a certain amount of displacement the lower part of the rock slide mass reaches stable slope conditions (shear strength of the sliding zone material exceeds the shear stress acting on the sliding zone) and acts as a resisting mass for the still unstable upper part of the slope. Furthermore numerical models show that secondary slides at the lower part of the slope have a similar effect. In both case cases the observed slope stabilisation can be clearly attributed to the formation of natural buttressing masses at the toe.

Possibilities of rock constitutive modelling and simulations

NASA Astrophysics Data System (ADS)

Baranowski, Paweł; Małachowski, Jerzy

2018-01-01

The paper deals with a problem of rock finite element modelling and simulation. The main intention of authors was to present possibilities of different approaches in case of rock constitutive modelling. For this purpose granite rock was selected, due to its wide mechanical properties recognition and prevalence in literature. Two significantly different constitutive material models were implemented to simulate the granite fracture in various configurations: Johnson - Holmquist ceramic model which is very often used for predicting rock and other brittle materials behavior, and a simple linear elastic model with a brittle failure which can be used for simulating glass fracturing. Four cases with different loading conditions were chosen to compare the aforementioned constitutive models: uniaxial compression test, notched three-point-bending test, copper ball impacting a block test and small scale blasting test.

Extended Horizontal Jet Drilling for EGS applications in Petrothermal Environments

NASA Astrophysics Data System (ADS)

Hahn, Simon; Duda, Mandy; Stoeckhert, Ferdinand; Wittig, Volker; Bracke, Rolf

2017-04-01

Extended Horizontal Jet Drilling for EGS applications in Petrothermal Environments S. Hahn, M. Duda, F. Stoeckhert, V. Wittig, R. Bracke International Geothermal Centre Bochum High pressure water jet drilling technologies are widely used in the drilling industry. Especially in geothermal and hard rock applications, horizontal (radial) jet drilling is, however, confronted with several limitations like lateral length, hole size and steerability. In order to serve as a serious alternative to conventional stimulation techniques these high pressure jetting techniques are experimentally investigated to gain fundamental knowledge about the fluid-structure interaction, to enhance the rock failing process and to identify the governing drilling parameters. The experimental program is divided into three levels. In a first step jetting experiments are performed under free surface conditions while logging fluid pressures, flow speeds and extracted rock volume. All process parameters are quantified with a self-developed jet-ability index and compared to the rock properties (density, porosity, permeability, etc.). In a second step experiments will be performed under pressure-controlled conditions. A test bench is currently under construction offering the possibility to assign an in-situ stress field to the specimen while penetrating the rock sample with a high pressure water jet or a radial jet drilling device. The experimental results from levels 1 and 2 allow to identify the governing rock failure mechanisms and to correlate them with physical rock properties and limited reservoir conditions. Results of the initial tests do show a clear dependency of achievable penetration depth on the interaction of jetting and rock parameters and an individual threshold of the nozzle outlet velocity can be noticed in order to successfully penetrate different formation types. At level 3 jetting experiments will be performed at simulated reservoir conditions corresponding to 5.000 m depth (e.g. up to 1.250 bar and 180 °C) on large samples with a diameter of 25 cm and a length of up to 3m using GZB's in-situ borehole and geofluid simulator 'iBOGS'. Experiments will be documented by active and passive ultrasound measurements and high speed imaging. Acknowledgement Jetting research and work at GZB has received funding in part from the European Union's Horizon 2020 research and innovation program under grant agreement No 654662 and also from federal government GER and state of NRW.

Visualising Three Dimensional Damage and Failure Envelopes: Implications for True Triaxial Deformation

NASA Astrophysics Data System (ADS)

Harland, S. R.; Browning, J.; Healy, D.; Meredith, P. G.; Mitchell, T. M.

2017-12-01

Ultimate failure in brittle rocks is commonly accepted to occur as a coalescence of micro-crack damage into a single failure plane. The geometry and evolution with stress of the cracks (damage) within the medium will play a role in dictating the geometry of the ultimate failure plane. Currently, the majority of experimental studies investigating damage evolution and rock failure use conventional triaxial stress states (σ1 > σ2 = σ3). Results from these tests can easily be represented on a Mohr-Coulomb plot (σn - τ), conveniently allowing the user to determine the geometry of the resultant failure plane. In reality however, stress in the subsurface is generally truly triaxial (σ1 > σ2 > σ3) and in this case, the Mohr-Coulomb failure criterion is inadequate as it incorporates no dependence on the intermediate stress (σ2), which has been shown to play an important role in controlling failure. It has recently been shown that differential stress is the key driver in initiating crack growth, regardless of the mean stress. Polyaxial failure criteria that incorporate the effect of the intermediate stress do exist and include the Modified Lade, Modified Wiebols and Cook, and the Drucker-Prager criteria. However, unlike the Mohr-Coulomb failure criterion, these polyaxial criteria do not offer any prediction of, or insight into, the geometry of the resultant failure plane. An additional downfall of all of the common conventional and polyaxial failure criteria is that they fail to describe the geometry of the damage (i.e. pre-failure microcracking) envelope with progressive stress; it is commonly assumed that the damage envelope is parallel to the ultimate brittle failure envelope. Here we use previously published polyaxial failure data for the Shirahama sandstone and Westerley granite to illustrate that the commonly used Mohr-Coulomb and polyaxial failure criteria do not sufficiently describe or capture failure or damage envelopes under true triaxial stress states. We investigate if and how Mohr-Coulomb type constructions can provide geometrical solutions to truly-triaxial problems. We look to incorporate both the intermediate stress and the differential stress as the controlling parameters in failure and examine the geometry of damage envelopes using damage onset data.

HPC simulations of grain-scale spallation to improve thermal spallation drilling

NASA Astrophysics Data System (ADS)

Walsh, S. D.; Lomov, I.; Wideman, T. W.; Potter, J.

2012-12-01

Thermal spallation drilling and related hard-rock hole opening techniques are transformative technologies with the potential to dramatically reduce the costs associated with EGS well drilling and improve the productivity of new and existing wells. In contrast to conventional drilling methods that employ mechanical means to penetrate rock, thermal spallation methods fragment rock into small pieces ("spalls") without contact via the rapid transmission of heat to the rock surface. State-of-the-art constitutive models of thermal spallation employ Weibull statistical failure theory to represent the relationship between rock heterogeneity and its propensity to produce spalls when heat is applied to the rock surface. These models have been successfully used to predict such factors as penetration rate, spall-size distribution and borehole radius from drilling jet velocity and applied heat flux. A properly calibrated Weibull model would permit design optimization of thermal spallation drilling under geothermal field conditions. However, although useful for predicting system response in a given context, Weibull models are by their nature empirically derived. In the past, the parameters used in these models were carefully determined from laboratory tests, and thus model applicability was limited by experimental scope. This becomes problematic, for example, if simulating spall production at depths relevant for geothermal energy production, or modeling thermal spallation drilling in new rock types. Nevertheless, with sufficient computational resources, Weibull models could be validated in the absence of experimental data by explicit small-scale simulations that fully resolve rock grains. This presentation will discuss how high-fidelity simulations can be used to inform Weibull models of thermal spallation, and what these simulations reveal about the processes driving spallation at the grain-scale - in particular, the role that inter-grain boundaries and micro-pores play in the onset and extent of spallation. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Solid images generated from UAVs to analyze areas affected by rock falls

NASA Astrophysics Data System (ADS)

Giordan, Daniele; Manconi, Andrea; Allasia, Paolo; Baldo, Marco

2015-04-01

The study of rock fall affected areas is usually based on the recognition of principal joints families and the localization of potential instable sectors. This requires the acquisition of field data, although as the areas are barely accessible and field inspections are often very dangerous. For this reason, remote sensing systems can be considered as suitable alternative. Recently, Unmanned Aerial Vehicles (UAVs) have been proposed as platform to acquire the necessary information. Indeed, mini UAVs (in particular in the multi-rotors configuration) provide versatility for the acquisition from different points of view a large number of high resolution optical images, which can be used to generate high resolution digital models relevant to the study area. By considering the recent development of powerful user-friendly software and algorithms to process images acquired from UAVs, there is now a need to establish robust methodologies and best-practice guidelines for correct use of 3D models generated in the context of rock fall scenarios. In this work, we show how multi-rotor UAVs can be used to survey areas by rock fall during real emergency contexts. We present two examples of application located in northwestern Italy: the San Germano rock fall (Piemonte region) and the Moneglia rock fall (Liguria region). We acquired data from both terrestrial LiDAR and UAV, in order to compare digital elevation models generated with different remote sensing approaches. We evaluate the volume of the rock falls, identify the areas potentially unstable, and recognize the main joints families. The use on is not so developed but probably this approach can be considered the better solution for a structural investigation of large rock walls. We propose a methodology that jointly considers the Structure from Motion (SfM) approach for the generation of 3D solid images, and a geotechnical analysis for the identification of joint families and potential failure planes.

A Reconsideration of the Extension Strain Criterion for Fracture and Failure of Rock

NASA Astrophysics Data System (ADS)

Wesseloo, J.; Stacey, T. R.

2016-12-01

The complex behaviours of rocks and rock masses have presented paradoxes to the rock engineer, including the fracturing of seemingly strong rock under low stress conditions, which often occurs near excavation boundaries. The extension strain criterion was presented as a fracture initiation criterion under these conditions (Stacey in Int J Rock Mech Min Sci 18:469-474, 1981). This criterion has been used successfully by some and criticised by others. In this paper, we review the literature on the extension strain criterion and present a case for the correct interpretation of the criterion and the conditions suitable for its use. We argue that the extension strain criterion can also be used to provide an indication of damage level under conditions of relatively low confining stress. We also present an augmentation of the criterion, the ultimate extension strain, which is applicable under extensional loading conditions when σ 2 is similar in magnitude to σ 1.

Crack propagation from a filled flaw in rocks considering the infill influences

NASA Astrophysics Data System (ADS)

Chang, Xu; Deng, Yan; Li, Zhenhua; Wang, Shuren; Tang, C. A.

2018-05-01

This study presents a numerical and experimental study of the cracking behaviour of rock specimen containing a single filled flaw under compression. The primary aim is to investigate the influences of infill on crack patterns, load-displacement response and specimen strength. The numerical code RFPA2D (Rock Failure Process Analysis) featured by the capability of modeling heterogeneous materials is employed to develop the numerical model, which is further calibrated by physical tests. The results indicate that there exists a critical infill strength which controls crack patterns for a given flaw inclination angle. For case of infill strength lower than the critical value, the secondary or anti-cracks are disappeared by increasing the infill strength. If the infill strength is greater than the critical value, the filled flaw has little influence on the cracking path and the specimen fails by an inclined crack, as if there is no flaw. The load-displacement responses show specimen stiffness increases by increasing infill strength until the infill strength reaches its critical value. The specimen strength increases by increasing the infill strength and almost keeps constant as the infill strength exceeds its critical value.

Comparison of Surface Properties in Natural and Artificially Generated Fractures in a Crystalline Rock

NASA Astrophysics Data System (ADS)

Vogler, Daniel; Walsh, Stuart D. C.; Bayer, Peter; Amann, Florian

2017-11-01

This work studies the roughness characteristics of fracture surfaces from a crystalline rock by analyzing differences in surface roughness between fractures of various types and sizes. We compare the surface properties of natural fractures sampled in situ and artificial (i.e., man-made) fractures created in the same source rock under laboratory conditions. The topography of the various fracture types is compared and characterized using a range of different measures of surface roughness. Both natural and artificial, and tensile and shear fractures are considered, along with the effects of specimen size on both the geometry of the fracture and its surface characterization. The analysis shows that fracture characteristics are substantially different between natural shear and artificial tensile fractures, while natural tensile fracture often spans the whole result domain of the two other fracture types. Specimen size effects are also evident, not only as scale sensitivity in the roughness metrics, but also as a by-product of the physical processes used to generate the fractures. Results from fractures generated with Brazilian tests show that fracture roughness at small scales differentiates fractures from different specimen sizes and stresses at failure.

Comparison and verification of two models which predict minimum principal in situ stress from triaxial data

DOE Office of Scientific and Technical Information (OSTI.GOV)

Harikrishnan, R.; Hareland, G.; Warpinski, N.R.

This paper evaluates the correlation between values of minimum principal in situ stress derived from two different models which use data obtained from triaxial core tests and coefficient for earth at rest correlations. Both models use triaxial laboratory tests with different confining pressures. The first method uses a vcrified fit to the Mohr failure envelope as a function of average rock grain size, which was obtained from detailed microscopic analyses. The second method uses the Mohr-Coulomb failure criterion. Both approaches give an angle in internal friction which is used to calculate the coefficient for earth at rest which gives themore » minimum principal in situ stress. The minimum principal in situ stress is then compared to actual field mini-frac test data which accurately determine the minimum principal in situ stress and are used to verify the accuracy of the correlations. The cores and the mini-frac stress test were obtained from two wells, the Gas Research Institute`s (GRIs) Staged Field Experiment (SFE) no. 1 well through the Travis Peak Formation in the East Texas Basin, and the Department of Energy`s (DOE`s) Multiwell Experiment (MWX) wells located west-southwest of the town of Rifle, Colorado, near the Rulison gas field. Results from this study indicates that the calculated minimum principal in situ stress values obtained by utilizing the rock failure envelope as a function of average rock grain size correlation are in better agreement with the measured stress values (from mini-frac tests) than those obtained utilizing Mohr-Coulomb failure criterion.« less

Risk Analysis and Prediction of Floor Failure Mechanisms at Longwall Face in Parvadeh-I Coal Mine using Rock Engineering System (RES)

NASA Astrophysics Data System (ADS)

Aghababaei, Sajjad; Saeedi, Gholamreza; Jalalifar, Hossein

2016-05-01

The floor failure at longwall face decreases productivity and safety, increases operation costs, and causes other serious problems. In Parvadeh-I coal mine, the timber is used to prevent the puncture of powered support base into the floor. In this paper, a rock engineering system (RES)-based model is presented to evaluate the risk of floor failure mechanisms at the longwall face of E 2 and W 1 panels. The presented model is used to determine the most probable floor failure mechanism, effective factors, damaged regions and remedial actions. From the analyzed results, it is found that soft floor failure is dominant in the floor failure mechanism at Parvadeh-I coal mine. The average of vulnerability index (VI) for soft, buckling and compressive floor failure mechanisms was estimated equal to 52, 43 and 30 for both panels, respectively. By determining the critical VI for soft floor failure mechanism equal to 54, the percentage of regions with VIs beyond the critical VI in E 2 and W 1 panels is equal to 65.5 and 30, respectively. The percentage of damaged regions showed that the excess amount of used timber to prevent the puncture of weak floor below the powered support base is equal to 4,180,739 kg. RES outputs and analyzed results showed that setting and yielding load of powered supports, length of face, existent water at face, geometry of powered supports, changing the cutting pattern at longwall face and limiting the panels to damaged regions with supercritical VIs could be considered to control the soft floor failure in this mine. The results of this research could be used as a useful tool to identify the damaged regions prior to mining operation at longwall panel for the same conditions.

Fan-structure waves in shear ruptures

NASA Astrophysics Data System (ADS)

Tarasov, Boris

2016-04-01

This presentation introduces a recently identified shear rupture mechanism providing a paradoxical feature of hard rocks - the possibility of shear rupture propagation through the highly confined intact rock mass at shear stress levels significantly less than frictional strength. According to the fan-mechanism the shear rupture propagation is associated with consecutive creation of small slabs in the fracture tip which, due to rotation caused by shear displacement of the fracture interfaces, form a fan-structure representing the fracture head. The fan-head combines such unique features as: extremely low shear resistance (below the frictional strength), self-sustaining stress intensification in the rupture tip (providing easy formation of new slabs), and self-unbalancing conditions in the fan-head (making the failure process inevitably spontaneous and violent). An important feature of the fan-mechanism is the fact that for the initial formation of the fan-structure an enhanced local shear stress is required, however, after completion of the fan-structure it can propagate as a dynamic wave through intact rock mass at shear stresses below the frictional strength. Paradoxically low shear strength of pristine rocks provided by the fan-mechanism determines the correspondingly low transient strength of the lithosphere, which favours generation of new earthquake faults in the intact rock mass adjoining pre-existing faults in preference to frictional stick-slip instability along these faults. The new approach reveals an alternative role of pre-existing faults in earthquake activity: they represent local stress concentrates in pristine rock adjoining the fault where special conditions for the fan-mechanism nucleation are created, while further dynamic propagation of the new fault (earthquake) occurs at low field stresses even below the frictional strength.

Modelisation numerique de tunnels de metro dans les massifs rocheux sedimentaires de la region de Montreal

NASA Astrophysics Data System (ADS)

Lavergne, Catherine

Geological formations of the Montreal area are mostly made of limestones. The usual approach for design is based on rock mass classification systems considering the rock mass as an equivalent continuous and isotropic material. However, for shallow excavations, stability is generally controlled by geological structures, that in Montreal, are bedding plans that give to the rock mass a strong strain and stress anisotropy. Objects of the research are to realize a numerical modeling that considers sedimentary rocks anisotropy and to determine the influence of the design parameters on displacements, stresses and failure around metro unsupported underground excavations. Geotechnical data used for this study comes from a metro extension project and has been made available to the author. The excavation geometries analyzed are the tunnel, the station and a garage consisting of three (3) parallel tunnels for rock covered between 4 and 16 m. The numerical modeling has been done with FLAC software that represents continuous environment, and ubiquitous joint behavior model to simulate strength anisotropy of sedimentary rock masses. The model considers gravity constraints for an anisotropic material and pore pressures. In total, eleven (11) design parameters have been analyzed. Results show that unconfined compressive strength of intact rock, fault zones and pore pressures in soils have an important influence on the stability of the numerical model. The geometry of excavation, the thickness of rock covered, the RQD, Poisson's ratio and the horizontal tectonic stresses have a moderate influence. Finally, ubiquitous joint parameters, pore pressures in rock mass, width of the pillars of the garage and the damage linked to the excavation method have a low impact. FLAC results have been compared with those of UDEC, a software that uses the distinct element method. Similar conclusions were obtained on displacements, stress state and failure modes. However, UDEC model give slightly less conservative results than FLAC. This study stands up by his local character and the large amount of geotechnical data available used to determine parameters of the numerical model. The results led to recommendations for laboratory tests that can be applied to characterize more specifically anisotropy of sedimentary rocks.

Association of apical rocking with long-term major adverse cardiac events in patients undergoing cardiac resynchronization therapy.

PubMed

Ghani, Abdul; Delnoy, Peter Paul H M; Ottervanger, Jan Paul; Ramdat Misier, Anand R; Smit, Jaap Jan J; Adiyaman, Ahmet; Elvan, Arif

2016-02-01

Correctly identifying patients who will benefit from cardiac resynchronization therapy (CRT) is still challenging. 'Apical rocking' is observed in asynchronously contracting ventricles and is associated with echocardiographic response to CRT. The association of apical rocking and long-term clinical outcome is however unknown at present. We assessed the predictive value of left ventricular (LV) apical rocking on a long-term clinical outcome in patients treated with CRT. Consecutive heart failure patients treated with primary indication for CRT-D between 2005 and 2009 were included in a prospective registry. Echocardiography was performed prior to CRT to assess apical rocking, defined as motion of the LV apical myocardium perpendicular to the LV long axis. Major adverse cardiac event (MACE) was defined as combined end point of cardiac death and/or heart failure hospitalization and/or appropriate therapy (ATP and/or ICD shocks). All echocardiograms were assessed by independent cardiologists, blinded for clinical data. Multivariable analyses were performed to adjust for potential confounders. Two hundred and ninety-five patients with echocardiography prior to implantation were included in the final analyses. Apical rocking was present in 45% of the study patients. Apical rocking was significantly more common in younger patients, females, patients with sinus rhythm, non-ischaemic cardiomyopathy, and in patients with LBBB and wider QRS duration. During a mean clinical follow-up of 5.2 ± 1.6 years, 92 (31%) patients reached the end point of the study (MACE). Patients with MACE had shorter QRS duration, had more ischaemic cardiomyopathy, and were more often on Amiodarone. In univariate analyses, MACE was associated with shorter QRS duration, ischaemic aetiology, and the absence of apical rocking. After multivariable analyses, apical rocking was associated with less MACE (hazards ratio, HR 0.44, 95% confidence interval, CI 0.25-0.77). Apical rocking is an independent predictor of a favourable long-term outcome in CRT-D patients. Published on behalf of the European Society of Cardiology. All rights reserved. © The Author 2015. For permissions please email: journals.permissions@oup.com.

Landslide processes in saprolitic soils of a tropical rain forest, Puerto Rico

USGS Publications Warehouse

Larsen, Matthew C.; Simon, Andrew; Larue, D.K.; Draper, G.

1990-01-01

Slickensides are present in the saprolite along relict fractures and joints derived from the parent rock; they are common in quartz-diorite bedrock, and less so in marine-deposited volcaniclastic bedrock. The failure planes of many landslides have exposed these relict fractures and joints as slickensides, and landslides appear to move on these pre-existing planes of weakness in the saprolite. The larges landslides (areas greater than 20,000 m2, however, are those that fail along saprolite-bedrock boundaries, which are zones of contrasting density and permeability within or at the base of the weathered profile.

Lithology and Bedrock Geotechnical Properties in Controlling Rock and Ice Mass Movements in Mountain Cryosphere

NASA Astrophysics Data System (ADS)

Karki, A.; Kargel, J. S.

2017-12-01

Landslides and ice avalanches kill >5000 people annually (D. Petley, 2012, Geology http://dx.doi.org/10.1130/G33217.1); destroy or damage homes and infrastructure; and create secondary hazards, such as flooding due to blocked rivers. Critical roles of surface slope, earthquake shaking, soil characteristics and saturation, river erosional undercutting, rainfall intensity, snow loading, permafrost thaw, freeze-thaw and frost shattering, debuttressing of unstable masses due to glacier thinning, and vegetation burn or removal are well-known factors affecting landslides and avalanches. Lithology-dependent bedrock physicochemical-mechanical properties—especially brittle elastic and shear strength, and chemical weathering properties that affect rock strength, are also recognized controls on landsliding and avalanching, but are not commonly considered in detail in landslide susceptibility assessment. Lithology controls the formation of weakened, weathered bedrock; the formation and accumulation of soils; soil saturation-related properties of grain size distribution, porosity, and permeability; and soil creep related to soil wetting-drying and freeze-thaw. Lithology controls bedrock abrasion and glacial erosion and debris production rates, the formation of rough or smoothed bedrock surface by glaciation, fluvial, and freeze-thaw processes. Lithologic variability (e.g., bedding; fault and joint structure) affects contrasts in chemical weathering rates, porosity, and susceptibility to frost shattering and chemical weathering, hence formation of overhanging outcrops and weakened slip planes. The sudden failure of bedrock or sudden slip of ice on bedrock, and many other processes depend on rock lithology, microstructure (porosity and permeability), and macrostructure (bedding; faults). These properties are sometimes considered in gross terms for landslide susceptibility assessment, but in detailed applications to specific development projects, and in detailed mapping over large areas, the details of rock lithology, weathering state, and structure are rarely considered. We have initiated a geological and rock mechanical properties approach to landslide susceptibility assessments in areas of high concern for human and infrastructure safety.

PDC Bit Testing at Sandia Reveals Influence of Chatter in Hard-Rock Drilling

DOE Office of Scientific and Technical Information (OSTI.GOV)

RAYMOND,DAVID W.

1999-10-14

Polycrystalline diamond compact (PDC) bits have yet to be routinely applied to drilling the hard-rock formations characteristic of geothermal reservoirs. Most geothermal production wells are currently drilled with tungsten-carbide-insert roller-cone bits. PDC bits have significantly improved penetration rates and bit life beyond roller-cone bits in the oil and gas industry where soft to medium-hard rock types are encountered. If PDC bits could be used to double current penetration rates in hard rock geothermal well-drilling costs could be reduced by 15 percent or more. PDC bits exhibit reasonable life in hard-rock wear testing using the relatively rigid setups typical of laboratorymore » testing. Unfortunately, field experience indicates otherwise. The prevailing mode of failure encountered by PDC bits returning from hard-rock formations in the field is catastrophic, presumably due to impact loading. These failures usually occur in advance of any appreciable wear that might dictate cutter replacement. Self-induced bit vibration, or ''chatter'', is one of the mechanisms that may be responsible for impact damage to PDC cutters in hard-rock drilling. Chatter is more severe in hard-rock formations since they induce significant dynamic loading on the cutter elements. Chatter is a phenomenon whereby the drillstring becomes dynamically unstable and excessive sustained vibrations occur. Unlike forced vibration, the force (i.e., weight on bit) that drives self-induced vibration is coupled with the response it produces. Many of the chatter principles derived in the machine tool industry are applicable to drilling. It is a simple matter to make changes to a machine tool to study the chatter phenomenon. This is not the case with drilling. Chatter occurs in field drilling due to the flexibility of the drillstring. Hence, laboratory setups must be made compliant to observe chatter.« less

Prediction of Fracture Behavior in Rock and Rock-like Materials Using Discrete Element Models

NASA Astrophysics Data System (ADS)

Katsaga, T.; Young, P.

2009-05-01

The study of fracture initiation and propagation in heterogeneous materials such as rock and rock-like materials are of principal interest in the field of rock mechanics and rock engineering. It is crucial to study and investigate failure prediction and safety measures in civil and mining structures. Our work offers a practical approach to predict fracture behaviour using discrete element models. In this approach, the microstructures of materials are presented through the combination of clusters of bonded particles with different inter-cluster particle and bond properties, and intra-cluster bond properties. The geometry of clusters is transferred from information available from thin sections, computed tomography (CT) images and other visual presentation of the modeled material using customized AutoCAD built-in dialog- based Visual Basic Application. Exact microstructures of the tested sample, including fractures, faults, inclusions and void spaces can be duplicated in the discrete element models. Although the microstructural fabrics of rocks and rock-like structures may have different scale, fracture formation and propagation through these materials are alike and will follow similar mechanics. Synthetic material provides an excellent condition for validating the modelling approaches, as fracture behaviours are known with the well-defined composite's properties. Calibration of the macro-properties of matrix material and inclusions (aggregates), were followed with the overall mechanical material responses calibration by adjusting the interfacial properties. The discrete element model predicted similar fracture propagation features and path as that of the real sample material. The path of the fractures and matrix-inclusion interaction was compared using computed tomography images. Initiation and fracture formation in the model and real material were compared using Acoustic Emission data. Analysing the temporal and spatial evolution of AE events, collected during the sample testing, in relation to the CT images allows the precise reconstruction of the failure sequence. Our proposed modelling approach illustrates realistic fracture formation and growth predictions at different loading conditions.

Rock and stone weathering at Citadel fortifications, Gozo (Malta): benefits from terrestrial laser scanning combined with conventional investigations

NASA Astrophysics Data System (ADS)

Tapete, D.; Gigli, G.; Mugnai, F.; Vannocci, P.; Pecchioni, E.; Morelli, S.; Fanti, R.; Casagli, N.

2012-04-01

Military architecture heritage is frequently built on rock masses affected by slope instability and weathering processes, which progressively undermine the foundations and cause collapses and toppling of the masonries. The latter can be also weakened by alteration of the stone surfaces, as a consequence of the interactions with the local environmental conditions. These conservation issues are emphasized for those sites, whose susceptibility to structural damages is also due to the similarity between the lithotypes constituting the geologic substratum and the construction materials. Effective solutions for the protection from such a type of phenomena can be achieved if the whole "rock mass - built heritage system" is analyzed. In this perspective, we propose a new approach for the study of the weathering processes affecting historic hilltop sites, taking benefits from the combination of terrestrial laser scanning (TLS) and conventional investigations, the latter including geotechnical and minero-petrographic analyses. In particular, the results here presented were obtained from specific tests on the fortifications of Citadel, Gozo (Malta), performed in co-operation with the Restoration Unit, Works Division, Maltese Ministry for Resources and Rural Affairs and the private company Politecnica Ingegneria e Architettura. The Citadel fortifications are built at the top of a relatively stiff and brittle limestone plate, formed by Upper Coralline Limestone (UCL) and overlying a thick Blue Clay (BC) layer. Differential weathering creates extensively fractured ledges on the cap and erosion niches in the strata beneath, thereby favouring block detachment, even rockfall events, such as the last one occurred in 2001. The locally quarried Globigerina Limestone (GL), historically employed in restoration masonries, is also exposed to alveolization and powdering, and several collapses damaged the underwalling interventions. Since the erosion pattern distribution suggested a correlation with the structural setting of the rock mass and the mineralogical properties of the limestones, an overall weathering study was carried out, by combining surface surveys with analyses of the inner structure. A holistic TLS point cloud of Citadel, produced by Consorzio Ferrara Ricerche of the University of Ferrara and made available by the Restoration Unit, was exploited to perform a 3D quantitative kinematic analysis of the entire rock mass. Each sector was classified in relation to the probability of occurrence of instability mechanisms, among which plane failure, block toppling and wedge failure. The latter was found associated with the highest index measured (30%), followed by the flexural toppling mechanism (17%), providing a confirmation to the field survey and the results of geotechnical analyses. The integration with geologic and diagnostic investigations (e.g., boreholes, thin section observations) highlighted the intrinsic weaknesses of the rocks and stones to weathering, with a quite unexpected higher susceptibility to erosion and disaggregation characterizing the inner layers. Hence, the textural appearance of the erosion surfaces, the rock/stone structural properties and the TLS-based classification of the cliff sectors were mutually correlated, and the most unstable areas were mapped. As main implication for the conservation, on site monitoring system (i.e., biaxial inclinometers and crack gauges) was installed and targeted restorations have been properly designed.

Rock Burst Monitoring by Integrated Microseismic and Electromagnetic Radiation Methods

NASA Astrophysics Data System (ADS)

Li, Xuelong; Wang, Enyuan; Li, Zhonghui; Liu, Zhentang; Song, Dazhao; Qiu, Liming

2016-11-01

For this study, microseismic (MS) and electromagnetic radiation (EMR) monitoring systems were installed in a coal mine to monitor rock bursts. The MS system monitors coal or rock mass ruptures in the whole mine, whereas the EMR equipment monitors the coal or rock stress in a small area. By analysing the MS energy, number of MS events, and EMR intensity with respect to rock bursts, it has been shown that the energy and number of MS events present a "quiet period" 1-3 days before the rock burst. The data also show that the EMR intensity reaches a peak before the rock burst and this EMR intensity peak generally corresponds to the MS "quiet period". There is a positive correlation between stress and EMR intensity. Buckling failure of coal or rock depends on the rheological properties and occurs after the peak stress in the high-stress concentration areas in deep mines. The MS "quiet period" before the rock burst is caused by the heterogeneity of the coal and rock structures, the transfer of high stress into internal areas, locked patches, and self-organized criticality near the stress peak. This study increases our understanding of coal and rock instability in deep mines. Combining MS and EMR to monitor rock burst could improve prediction accuracy.

Experimental investigation and constitutive model for lime mudstone.

PubMed

Wang, Junbao; Liu, Xinrong; Zhao, Baoyun; Song, Zhanping; Lai, Jinxing

2016-01-01

In order to investigate the mechanical properties of lime mudstone, conventional triaxial compression tests under different confining pressures (0, 5, 15 and 20 MPa) are performed on lime mudstone samples. The test results show that, from the overall perspective of variation law, the axial peak stress, axial peak strain and elastic modulus of lime mudstone tend to gradually increase with increasing confining pressure. In the range of tested confining pressure, the variations in axial peak stress and elastic modulus with confining pressure can be described with linear functions; while the variation in axial peak strain with confining pressure can be reflected with a power function. To describe the axial stress-strain behavior in failure process of lime mudstone, a new constitutive model is proposed, with the model characteristics analyzed and the parameter determination method put forward. Compared with Wang' model, only one parameter n is added to the new model. The comparison of predicted curves from the model and test data indicates that the new model can preferably simulate the strain softening property of lime mudstone and the axial stress-strain response in rock failure process.

Load-Unload Response Ratio (LURR), Accelerating Moment/Energy Release (AM/ER) and State Vector Saltation as Precursors to Failure of Rock Specimens

NASA Astrophysics Data System (ADS)

Yin, Xiang-Chu; Yu, Huai-Zhong; Kukshenko, Victor; Xu, Zhao-Yong; Wu, Zhishen; Li, Min; Peng, Keyin; Elizarov, Surgey; Li, Qi

2004-12-01

In order to verify some precursors such as LURR (Load/Unload Response Ratio) and AER (Accelerating Energy Release) before large earthquakes or macro-fracture in heterogeneous brittle media, four acoustic emission experiments involving large rock specimens under tri-axial stress, have been conducted. The specimens were loaded in two ways: monotonous or cycling. The experimental results confirm that LURR and AER are precursors of macro-fracture in brittle media. A new measure called the state vector has been proposed to describe the damage evolution of loaded rock specimens.

The Remote Detection of Incipient Catastrophic Failure in Large Landslides

NASA Astrophysics Data System (ADS)

Petley, D.; Bulmer, M. H.; Murphy, W.; Mantovani, F.

2001-12-01

Landslide movement is commonly associated with brittle failure and ductile deformation. Kilburn and Petley (2001) proposed that cracking in landslides occurs due to downslope stress acting on the deforming horizon. If the assumption that a given crack event breaks a fixed distance of unbroken rock or soil the rate of cracking becomes equivalent to the number of crack events per unit time. Where crack growth (not nucleation) is occurring, the inverse rate of displacement changes linearly with time. Failure can be assumed to be the time at which displacement rates become infinitely large. Thus, for a slope heading towards catastrophic failure due to the development of a failure plane, this relationship would be linear, with the point at which failure will occur being the time when the line intercepts the x-axis. Increasing rates of deformation associated with ductile processes of crack nucleation would yield a curve with a negative gradient asymptopic to the x-axis. This hypothesis is being examined. In the 1960 movement of the Vaiont slide, Italy, although the rate of movement was accelerating, the plot of 1/deformation against time shows that it was increasing towards a steady state deformation. This movement has been associated with a low accumulated strain ductile phase of movement. In the 1963 movement event, the trend is linear. This was associated with a brittle phase of movement. A plot of 1/deformation against time for movement of the debris flow portion of the Tessina landslide (1998) shows a curve with a negative gradient asymptopic to the x-axis. This indicates that the debris flow moved as a result of ductile deformation processes. Plots of movement data for the Black Ven landslide over 1999 and 2001 also show curves that correlate with known deformation and catastrophic phases. The model results suggest there is a definable deformation pattern that is diagnostic of landslides approaching catastrophic failure. This pattern can be differentiated from landslides that are undergoing ductile deformation and those that are suffering crack nucleation.

Rock gabion, rip-rap, and culvert treatments: Successes and failures in post-fire erosion mitigation, Schultz Fire 2010

Treesearch

Daniel G. Neary; Karen A. Koestner

2011-01-01

Following the Schultz Fire in June of 2010, several erosion mitigation efforts were undertaken to reduce the impacts of post-fire flooding expected during the 2010 monsoon. One treatment consisted of the placement of large rock rip-rap on targeted fill slopes of a high elevation forest road that contains a buried pipeline supplying water to the city of Flagstaff....

Computational upscaling of Drucker-Prager plasticity from micro-CT images of synthetic porous rock

NASA Astrophysics Data System (ADS)

Liu, Jie; Sarout, Joel; Zhang, Minchao; Dautriat, Jeremie; Veveakis, Emmanouil; Regenauer-Lieb, Klaus

2018-01-01

Quantifying rock physical properties is essential for the mining and petroleum industry. Microtomography provides a new way to quantify the relationship between the microstructure and the mechanical and transport properties of a rock. Studies reporting the use microtomographic images to derive permeability and elastic moduli of rocks are common; only rare studies were devoted to yield and failure parameters using this technique. In this study, we simulate the macroscale plastic properties of a synthetic sandstone sample made of calcite-cemented quartz grains using the microscale information obtained from microtomography. The computations rely on the concept of representative volume elements (RVEs). The mechanical RVE is determined using the upper and lower bounds of finite-element computations for elasticity. We present computational upscaling methods from microphysical processes to extract the plasticity parameters of the RVE and compare results to experimental data. The yield stress, cohesion and internal friction angle of the matrix (solid part) of the rock were obtained with reasonable accuracy. Computations of plasticity of a series of models of different volume-sizes showed almost overlapping stress-strain curves, suggesting that the mechanical RVE determined by elastic computations is also valid for plastic yielding. Furthermore, a series of models were created by self-similarly inflating/deflating the porous models, that is keeping a similar structure while achieving different porosity values. The analysis of these models showed that yield stress, cohesion and internal friction angle linearly decrease with increasing porosity in the porosity range between 8 and 28 per cent. The internal friction angle decreases the most significantly, while cohesion remains stable.

Macro-mesoscopic Fracture and Strength Character of Pre-cracked Granite Under Stress Relaxation Condition

NASA Astrophysics Data System (ADS)

Liu, Junfeng; Yang, Haiqing; Xiao, Yang; Zhou, Xiaoping

2018-05-01

The fracture characters are important index to study the strength and deformation behavior of rock mass in rock engineering. In order to investigate the influencing mechanism of loading conditions on the strength and macro-mesoscopic fracture character of rock material, pre-cracked granite specimens are prepared to conduct a series of uniaxial compression experiments. For parts of the experiments, stress relaxation tests of different durations are also conducted during the uniaxial loading process. Furthermore, the stereomicroscope is adopted to observe the microstructure of the crack surfaces of the specimens. The experimental results indicate that the crack surfaces show several typical fracture characters in accordance with loading conditions. In detail, some cleavage fracture can be observed under conventional uniaxial compression and the fractured surface is relatively rough, whereas as stress relaxation tests are attached, relative slip trace appears between the crack faces and some shear fracture starts to come into being. Besides, the crack faces tend to become smoother and typical terrace structures can be observed in local areas. Combining the macroscopic failure pattern of the specimens, it can be deduced that the duration time for the stress relaxation test contributes to the improvement of the elastic-plastic strain range as well as the axial peak strength for the studied material. Moreover, the derived conclusion is also consistent with the experimental and analytical solution for the pre-peak stage of the rock material. The present work may provide some primary understanding about the strength character and fracture mechanism of hard rock under different engineering environments.

Numerical Investigation of the Effect of the Location of Critical Rock Block Fracture on Crack Evolution in a Gob-side Filling Wall

NASA Astrophysics Data System (ADS)

Li, Xuehua; Ju, Minghe; Yao, Qiangling; Zhou, Jian; Chong, Zhaohui

2016-03-01

Generation, propagation, and coalescence of the shear and tensile cracks in the gob-side filling wall are significantly affected by the location of the fracture of the critical rock block. The Universal Discrete Element Code software was used to investigate crack evolution characteristics in a gob-side filling wall and the parameter calibration process for various strata and the filling wall was clearly illustrated. The cracks in both the filling wall and the coal wall propagate inward in a V-shape pattern with dominant shear cracks generated initially. As the distance between the fracture and the filling wall decreases, the number of cracks in the filling wall decreases, and the stability of the filling wall gradually improves; thus, by splitting the roof rock at the optimal location, the filling wall can be maintained in a stable state. Additionally, we conducted a sensitivity analysis that demonstrated that the higher the coal seam strength, the fewer cracks occur in both the filling wall and the coal wall, and the less failure they experience. With the main roof fracturing into a cantilever structure, the higher the immediate roof strength, the fewer cracks are in the filling wall. With the critical rock block fracturing above the roadway, an optimal strength of the immediate roof can be found that will stabilize the filling wall. This study presents a theoretical investigation into stabilization of the filling wall, demonstrating the significance of pre-splitting the roof rock at a desirable location.

The influence of pore textures on the permeability of volcanic rocks

NASA Astrophysics Data System (ADS)

Mueller, S.; Spieler, O.; Scheu, B.; Dingwell, D.

2006-12-01

The permeability of a porous medium is strongly dependent on its porosity, as a higher proportion of pore volume is generally expected to lead to a greater probability of pore interconnectedness and the formation of a fluid-flow providing pathway. However, the relationship between permeability and porosity is not a unique one, as many other textural parameters may play an important role and substantially affect gas flow properties. Among these parameters are (a) the connection geometry (i.e. intergranular pore spaces in clastic sediments vs. bubble interconnections), (b) the pore sizes, (c) pore shape and (d) pore size distribution. The gas permeability of volcanic rocks may influence various eruptive processes. The transition from a quiescent degassing dome to rock failure (fragmentation) may, for example, be controlled by the rock's permeability, in as much as it affects the speed by which a gas overpressure in vesicles is reduced in response to decompression. It is therefore essential to understand and quantify influences of different pore textures on the degassing properties of volcanic rocks, as well as investigate the effects of permeability on eruptive processes. Using a modified shock-tube-based fragmentation apparatus, we have measured unsteady-state permeability at a high initial pressure differential. Following sudden decompression above the rock cylinder, pressurized gas flows through the sample in a steel autoclave. A transient 1D filtration code has been developed to calculate permeability using the experimental pressure decay curve within a defined volume below the sample. An external furnace around the autoclave and the use of compressed salt as sealant allows also measurements at high temperatures up to 800 °C. Over 130 permeability measurements have been performed on samples of different volcanic settings, covering a wide range of porosity. The results show a general positive relationship between porosity and permeability with a high data scatter. Analysis of the samples eruptive origin as well as the pore sizes, shapes and size distribution allow an estimation of the contribution of various textural effects to the overall permeability.

A new design concept of fully grouted rock bolts in underground construction

NASA Astrophysics Data System (ADS)

Phich Nguyen, Quang; Nguyen, Van Manh; Tuong Nguyen, Ke

2018-04-01

The main problem after excavating an underground excavation is to maintain the stability of the excavation for a certain period of time. Failure in meeting this demand is a threat to safety of men and equipment. Support and reinforcement are different instruments with different mechanisms. Among the common support systems in tunnelling and mining, rock bolts have been widely used to reinforce rock mass and also to reduce geological hazards. Furthermore rock bolts can be applied under varying different geological conditions with cost-effectiveness. Although different methods are developed for grouted rock bolts design until now, the interaction mechanism of the rock bolts and rock mass is still very complicated issue. The paper addresses an analytical model for the analysis and design of fully grouted rock bolts based on the reinforcement principle. According to this concept the jointed rock mass reinforced by grouted rock bolts is considered as composite material which includes rock mass, the grout material and the bolt shank. The mechanical properties of this composite material depend on the ratio of the components. The closed-form solution was developed based on the assumption that the rock mass arround a circular tunnel remained elastic after installing fully grouted rock bolts. The main parameters of the rock-bolt system (the diameter and length of bolt shank, the space between the bolts) are then easily estimated from the obtained solution.

The Sasso Pizzuto landslide dam and seismically induced rockfalls along the Nera River gorge (Central Italy).

NASA Astrophysics Data System (ADS)

Romeo, Saverio; Di Matteo, Lucio; Melelli, Laura; Cencetti, Corrado; Dragoni, Walter; Fredduzzi, Andrea; De Rosa, Pierluigi

2017-04-01

The seismically induced landslides are among the most destructive and dangerous effects of an earthquake. In the Italian contest, this is also documented by a national catalogue that collects data related to earthquake-induced ground failures in the last millennium (CEDIT database). In particular, Central Italy has been affected by several historical landslides triggered by significant earthquakes, the last of which occurred in August-October 2016, representing the Italian strongest event after the 1980 Irpinia earthquake (Mw 6.9). The study presents the effects of recent seismically induced rockfalls occurred within the Central Italy seismic sequence (October 30, 2016) along the Nera River gorge between Umbria and Marche. The study area is completely included in the Monti Sibillini National Park, where the highest mountain chain in the Umbrian-Marchean Apennine is located. Most of rockfalls have affected the "Maiolica" formation, a stratified and fractured pelagic limestone dating to the Early Cretaceous. The seismic sequence produced diffuse instabilities along the SP 209 road within the Nera River gorge: boulders, debris accumulations and diffuse rockfalls have been mapped. Most of boulders have size ranging from 0.3 to 2.0 m in diameter. Although several strong quakes (Mw > 5) occurred during the August-October sequence, only the main quake triggered the Sasso Pizzuto rockfall producing a landslide dam along the Nera River. The landslide appears to have originated as a wedge failure, which evolved to free fall when the rock block lost the contact with the stable rock mass. In other words, the quake produced the "explosion" of the rock wall allowing the rockfall process. Once the rock mass reached the toe of the slope, it was broken triggering a rock avalanche that obstructed both the Nera River and SP 209 road. With the aim to estimate the total volume of involved rock, a field survey was carried out by using a laser rangefinder. Remote measures were acquired taking into account the inclination, horizontal, vertical and slope distance. Through topographical calculations and GIS analysis, it has been possible to reconstruct the size and shape of debris accumulation estimating a volume of about 70000 m3 (±8000 m3 due to measurements accuracy). This agrees with qualitative measures independently performed. The maximum distance between the debris accumulation and rockfall source area is about 200 m; the altitude difference is 270 m. The landslide debris partially dammed the Nera River, generating a lake upstream: currently the stream is flowing on the road among debris.

Rockfall monitoring by Terrestrial Laser Scanning - case study of the basaltic rock face at Castellfollit de la Roca (Catalonia, Spain)

NASA Astrophysics Data System (ADS)

Abellán, A.; Vilaplana, J. M.; Calvet, J.; García-Sellés, D.; Asensio, E.

2011-03-01

This case study deals with a rock face monitoring in urban areas using a Terrestrial Laser Scanner. The pilot study area is an almost vertical, fifty meter high cliff, on top of which the village of Castellfollit de la Roca is located. Rockfall activity is currently causing a retreat of the rock face, which may endanger the houses located at its edge. TLS datasets consist of high density 3-D point clouds acquired from five stations, nine times in a time span of 22 months (from March 2006 to January 2008). The change detection, i.e. rockfalls, was performed through a sequential comparison of datasets. Two types of mass movement were detected in the monitoring period: (a) detachment of single basaltic columns, with magnitudes below 1.5 m3 and (b) detachment of groups of columns, with magnitudes of 1.5 to 150 m3. Furthermore, the historical record revealed (c) the occurrence of slab failures with magnitudes higher than 150 m3. Displacements of a likely slab failure were measured, suggesting an apparent stationary stage. Even failures are clearly episodic, our results, together with the study of the historical record, enabled us to estimate a mean detachment of material from 46 to 91.5 m3 year-1. The application of TLS considerably improved our understanding of rockfall phenomena in the study area.

The Effect of Experimental Weathering on the Multiscale Pore Structure of Granites: A (U)SANS, Imaging Analysis

NASA Astrophysics Data System (ADS)

Anovitz, L. M.; Sheets, J.; Gu, X.; Brantley, S.; Cole, D. R.; Ilton, E. S.; Mildner, D. F. R.; Littrell, K. C.; Gagnon, C.

2017-12-01

The microstructure and evolution of pore space is a critically important factor controlling fluid flow properties in geological formations, including the migration and retention of water, gas and hydrocarbons, sequestration of wastes, the formation of ore deposits, and the evolution of metamorphic terranes. As noted by Navarre-Sitchler et al. (2013), pristine igneous bedrock does not usually contain significant water. However, infiltration of meteoric water causes the rock to begin to disaggregate, increasing the porosity and surface area. In many igneous rocks this process is enhanced by oxidation. However, the mechanisms of porosity formation during weathering are poorly understood, and we cannot accurately extrapolate laboratory reaction rates to the field in predictive numerical models. While there are many methods for interrogating pore structure, it is difficult to satisfactorily describe textural and porosity changes in rock samples using direct imaging techniques because of the wide variation in length scales involved. A combination of SANS, USANS and imaging is, however, well suited to this task. The weathering process in granite is especially complex. While more mafic rocks tend to alter diffusively, forming altered rims, stresses caused by oxidation of ferromagnesian minerals—particularly biotites—tend to cause granites to spall. In order to better understand the effects of oxidation on the weathering process we have performed a series of experiments on granite cores approximately 5/8" in diameter by 5/8" long. These have been reacted in a solution of Se6+ at 200°C for periods of 1, 2, 4, 8, 16, 32, 64, 256 and 438 days. The reaction of Se6+ to Se4+ is very oxidizing relative to that of the Fe2+ in the granite, the solution contained enough to buffer twice the ferrous iron expected in the rock sample, and no secondary phases are expected to form. Because of the geometry these are expected to form oxidized rims that grow with time prior to failure, and the reactive porosity and micro-stress-fractures are easily discernable and quantifiable by (U)SANS. Annular Cd masks were used to isolate core and rim processes during the (U)SANS analyses. These were supplemented by SEM analyses. Results suggest that reactive stresses play a significant role in the evolution of porosity during weathering.

Columnar jointing - the mechanics of thermal contraction in cooling lavas

NASA Astrophysics Data System (ADS)

Lavallée, Y.; Iddon, F.; Hornby, A. J.; Kendrick, J. E.; von Aulock, F. W.; Wadsworth, F. B.

2014-12-01

Columnar joints are spectacular features of volcanic rocks, which form by cracking during cooling-induced contraction of lava. The process, and resultant geometry, manifests a complex interplay between heat dissipation, contraction and tensile strength, yet the formation temperature of such joints remains elusive. Here, we present results from a combination of field survey, thermo-analytical characterisation and mechanical investigation to constrain conditions favourable for columnar jointing. Columnar joints at Seljavellir, a basaltic lava flow at the base of Eyjafjallajökull volcano (Iceland) produce quadratic to heptagonal cross sectional patterns with column widths ranging from 20 to 70 cm in size. The fracture surfaces are characterised by striae with spacing (between 1 to 6 cm) that shares a positive linear relationship to the joint spacing. The striae exhibit both a rough and smooth portion, interpreted to express a change in deformation regime from a ductile response as stress builds up to a fully brittle, mode-I fracture propagation at high stress accumulation. To test the thermo-mechanics of columnar joints we developed an experimental setup to investigate the stress, strain-to-failure and temperature at which basalts undergo tensile failure during cooling from the solidus temperature of 980 °C. We find that fractures initiate at ~800 °C, revealed by a change in stress accumulation (i.e., Young modulus), and complete failure completes after some 0.4% strain at ~670 °C. We interpret the two-stage fracture dynamics as the cause for the change in fracture surface roughness observed in nature. We coupled this dataset with Brazil tensile tests at 30, 400, 600, 800 and 1000 °C. We note that the strain to failure decrease from 1% (>800 °C) to 0.4% (<800 °C). Complementary dilatometric measurements (at 3mN of normal stress and a rate of 2 C/min) constrain the expansion coefficient to be linear and equal to 10-5/°C below the solid temperature. Simple ratio between strain-to-failure and expansion coefficient suggests that 400 °C of cooling (from the solidus) is require to achieve tensile failure by thermal contraction, supporting the first suite of experiments. We conclude that columnar jointing is not a phenomenon that takes place in molten lava, but rather occurs well within the solid state of volcanic rocks.

True 3D kinematic analysis for slope instability assessment in the Siq of Petra (Jordan), from high resolution TLS

NASA Astrophysics Data System (ADS)

Gigli, Giovanni; Margottini, Claudio; Spizzichino, Daniele; Ruther, Heinz; Casagli, Nicola

2016-04-01

Most classifications of mass movements in rock slopes use relatively simple, idealized geometries for the basal sliding surface, like planar sliding, wedge sliding, toppling or columnar failures. For small volumes, the real sliding surface can be often well described by such simple geometries. Extended and complex rock surfaces, however, can exhibit a large number of mass movements, also showing various kind of kinematisms. As a consequence, the real situation in large rock surfaces with a complicate geometry is generally very complex and a site depending analysis, such as fieldwork and compass, cannot be comprehensive of the real situation. Since the outstanding development of terrestrial laser scanner (TLS) in recent years, rock slopes can now be investigated and mapped through high resolution point clouds, reaching the resolution of few mm's and accuracy less than a cm in most advanced instruments, even from remote surveying. The availability of slope surface digital data can offer a unique chance to determine potential kinematisms in a wide distributed area for all the investigated geomorphological processes. More in detail the proposed method is based on the definition of least squares fitting planes on clusters of points extracted by moving a sampling cube on the point cloud. If the associated standard deviation is below a defined threshold, the cluster is considered valid. By applying geometric criteria it is possible to join all the clusters lying on the same surface; in this way discontinuity planes can be reconstructed, rock mass geometrical properties are calculated and, finally, potential kinematisms established. The Siq of Petra (Jordan), is a 1.2 km naturally formed gorge, with an irregular horizontal shape and a complex vertical slope, that represents the main entrance to Nabatean archaeological site. In the Siq, discontinuities of various type (bedding, joints, faults), mainly related to geomorphological evolution of the slope, lateral stress released, stratigraphic setting and tectonic activity can be recognized. As a consequence, rock-falls have been occurring, even recently, with unstable rock mass volumes ranging from 0.1 m3 up to over some hundreds m3. Slope instability, acceleration of crack deformation and consequent increasing of rock-fall hazard conditions, could threaten the safety of tourist as well as the integrity of the heritage. 3D surface model coming from Terrestrial Laser Scanner acquisitions was developed almost all over the site of Petra, including the Siq. Comprehensively, a point cloud of five billion points was generated making the site of Petra likely the largest scanned archaeological site in the word. As far as the Siq, the scanner was positioned on the path floor at intervals of not more than 10 meters from each station. The total number of scans in the Siq was 220 with an average point cloud interval of approximately 3 cm. Subsequently, for the definition of the main rockfall source areas, a spatial kinematic analysis for the whole Siq has been performed, by using discontinuity orientation data extracted from the point cloud by means of the software Diana. Orientation, number of sets, spacing/frequency, persistence, block size and scale dependent roughness was obtained combining fieldwork and automatic analysis. This kind of analysis is able to establish where a particular instability mechanism is kinematically feasible, given the geometry of the slope, the orientation of discontinuities and shear strength of the rock. The final outcome of this project was a detail landslide kinematic index map, reporting main potential instability mechanisms for a given area. The kinematic index was finally calibrated for each instability mechanism (plane failure; wedge failure; block toppling; flexural toppling) surveyed in the site. The latter is including the collapse occurred in May 2015, likely not producing any victim, in a sector clearly identified by the susceptibility maps produced by the analysis.

Rock Mass Classification of Karstic Terrain in the Reservoir Slopes of Tekeze Hydropower Project

NASA Astrophysics Data System (ADS)

Hailemariam Gugsa, Trufat; Schneider, Jean Friedrich

2010-05-01

Hydropower reservoirs in deep gorges usually experience slope failures and mass movements. History also showed that some of these projects suffered severe landslides, which left lots of victims and enormous economic loss. Thus, it became vital to make substantial slope stability studies in such reservoirs to ensure safe project development. This study also presents a regional scale instability assessment of the Tekeze Hydropower reservoir slopes. Tekeze hydropower project is a newly constructed double arch dam that completed in August 2009. It is developed on Tekeze River, tributary of Blue Nile River that runs across the northern highlands of Ethiopia. It cuts a savage gorge 2000m deep, the deepest canyon in Africa. The dam is the highest dam in Ethiopia at 188m, 10 m higher than China's Three Gorges Dam. It is being developed by Chinese company at a cost of US350M. The reservoir is designed at 1140 m elevation, as retention level to store more than 9000 million m3 volume of water that covers an area of 150 km2, mainly in channel filling form. In this study, generation of digital elevation model from ASTER satellite imagery and surface field investigation is initially considered for further image processing and terrain parameters' analyses. Digitally processed multi spectral ASTER ortho-images drape over the DEM are used to have different three dimensional perspective views in interpreting lithological, structural and geomorphological features, which are later verified by field mapping. Terrain slopes are also delineated from the relief scene. A GIS database is ultimately developed to facilitate the delineation of geotechnical units for slope rock mass classification. Accordingly, 83 geotechnical units are delineated and, within them, 240 measurement points are established to quantify in-situ geotechnical parameters. Due to geotechnical uncertainties, four classification systems; namely geomorphic rock mass strength classification (RMS), slope mass rating (SMR), rock slope stability probability classification (SSPC) and geological strength index (GSI) are employed to classify the rock mass. The results are further compared with one another to delineate the instability conditions and produce an instability map of the reservoir slopes. Instability of the reservoir slopes is found to be mainly associated with daylighting discontinuities, thinly bedded/foliated slates, and karstified limestone. It is also noted that these features are mostly located in the regional gliding plane and shear zone, which are related with old slides scars. In general, the instabilities are found relatively far from the dam axis, in relatively less elevated and less steep slopes, which are going to be nearly covered by the impoundment; thus, they are normally expected to have less hazard in relation to the reservoir setting. Some minor failures will be generally expected during the reservoir filling.

Deep geothermal: The ‘Moon Landing’ mission in the unconventional energy and minerals space

DOE PAGES

Regenauer-Lieb, Klaus; Bunger, Andrew; Chua, Hui Tong; ...

2015-01-30

Deep geothermal from the hot crystalline basement has remained an unsolved frontier for the geothermal industry for the past 30 years. This poses the challenge for developing a new unconventional geomechanics approach to stimulate such reservoirs. While a number of new unconventional brittle techniques are still available to improve stimulation on short time scales, the astonishing richness of failure modes of longer time scales in hot rocks has so far been overlooked. These failure modes represent a series of microscopic processes: brittle microfracturing prevails at low temperatures and fairly high deviatoric stresses, while upon increasing temperature and decreasing applied stressmore » or longer time scales, the failure modes switch to transgranular and intergranular creep fractures. Accordingly, fluids play an active role and create their own pathways through facilitating shear localization by a process of time-dependent dissolution and precipitation creep, rather than being a passive constituent by simply following brittle fractures that are generated inside a shear zone caused by other localization mechanisms. We lay out a new paradigm for reservoir stimulation by reactivating pre-existing faults at reservoir scale in a reservoir scale aseismic, ductile manner. A side effect of the new “soft” stimulation method is that owing to the design specification of a macroscopic ductile response, the proposed method offers the potential of a safer control over the stimulation process compared to conventional stimulation protocols such as currently employed in shale gas reservoirs.« less

Diminishing friction of joint surfaces as initiating factor for destabilising permafrost rocks?

NASA Astrophysics Data System (ADS)

Funk, Daniel; Krautblatter, Michael

2010-05-01

Degrading alpine permafrost due to changing climate conditions causes instabilities in steep rock slopes. Due to a lack in process understanding, the hazard is still difficult to asses in terms of its timing, location, magnitude and frequency. Current research is focused on ice within joints which is considered to be the key-factor. Monitoring of permafrost-induced rock failure comprises monitoring of temperature and moisture in rock-joints. The effect of low temperatures on the strength of intact rock and its mechanical relevance for shear strength has not been considered yet. But this effect is signifcant since compressive and tensile strength is reduced by up to 50% and more when rock thaws (Mellor, 1973). We hypotheisze, that the thawing of permafrost in rocks reduces the shear strength of joints by facilitating the shearing/damaging of asperities due to the drop of the compressive/tensile strength of rock. We think, that decreasing surface friction, a neglected factor in stability analysis, is crucial for the onset of destabilisation of permafrost rocks. A potential rock slide within the permafrost zone in the Wetterstein Mountains (Zugspitze, Germany) is the basis for the data we use for the empirical joint model of Barton (1973) to estimate the peak shear strength of the shear plane. Parameters are the JRC (joint roughness coefficient), the JCS (joint compressive strength) and the residual friction angle (φr). The surface roughness is measured in the field with a profile gauge to create 2D-profiles of joint surfaces. Samples of rock were taken to the laboratory to measure compressive strength using a high-impact Schmidt-Hammer under air-dry, saturated and frozen conditions on weathered and unweathered surfaces. Plugs where cut out of the rock and sand blasted for shear tests under frozen and unfrozen conditions. Peak shear strength of frozen and unfrozen rocks will be calculated using Barton's model. First results show a mean decrease of compressive strength of around 40% when frozen water-saturated rock is exposed to thawing. The friction of sand-blasted rock-plugs decreases by a mean value of 32% considering degradation of rocks by freeze-thaw cycles. Surface roughness could be measured succesfully with the profile gauge and the results show a significant difference between untouched and sheared joint surfaces in the field. Here we show, that shear resistance of rock joints will be diminshed just by the thawing of intact rock. This study will help to establish a sound concept for the destabilization of rocks in permafrost and provide the data for first stability modelling. This will be crucial for predict rock instability in permafrost regions. References: Barton, N. (1973): Review of new shear strength criterion for rock jonts. Engineering Geology 7: 287-332 Mellor, M. (1973): Mechanical Properties of Rocks at Low Temperatures. 2nd International Conference on Permafrost, Yakutsk, Siberia, 334-343.

Seismic performance evaluation of an infilled rocking wall frame structure through quasi-static cyclic testing

NASA Astrophysics Data System (ADS)

Pan, Peng; Wu, Shoujun; Wang, Haishen; Nie, Xin

2018-04-01

Earthquake investigations have illustrated that even code-compliant reinforced concrete frames may suffer from soft-story mechanism. This damage mode results in poor ductility and limited energy dissipation. Continuous components offer alternatives that may avoid such failures. A novel infilled rocking wall frame system is proposed that takes advantage of continuous component and rocking characteristics. Previous studies have investigated similar systems that combine a reinforced concrete frame and a wall with rocking behavior used. However, a large-scale experimental study of a reinforced concrete frame combined with a rocking wall has not been reported. In this study, a seismic performance evaluation of the newly proposed infilled rocking wall frame structure was conducted through quasi-static cyclic testing. Critical joints were designed and verified. Numerical models were established and calibrated to estimate frame shear forces. The results evaluation demonstrate that an infilled rocking wall frame can effectively avoid soft-story mechanisms. Capacity and initial stiffness are greatly improved and self-centering behavior is achieved with the help of the infilled rocking wall. Drift distribution becomes more uniform with height. Concrete cracks and damage occurs in desired areas. The infilled rocking wall frame offers a promising approach to achieving seismic resilience.

Assessment of Mudrock Brittleness with Micro-scratch Testing

NASA Astrophysics Data System (ADS)

Hernandez-Uribe, Luis Alberto; Aman, Michael; Espinoza, D. Nicolas

2017-11-01

Mechanical properties are essential for understanding natural and induced deformational behavior of geological formations. Brittleness characterizes energy dissipation rate and strain localization at failure. Brittleness has been investigated in hydrocarbon-bearing mudrocks in order to quantify the impact of hydraulic fracturing on the creation of complex fracture networks and surface area for reservoir drainage. Typical well logging correlations associate brittleness with carbonate content or dynamic elastic properties. However, an index of rock brittleness should involve actual rock failure and have a consistent method to quantify it. Here, we present a systematic method to quantify mudrock brittleness based on micro-mechanical measurements from the scratch test. Brittleness is formulated as the ratio of energy associated with brittle failure to the total energy required to perform a scratch. Soda lime glass and polycarbonate are used for comparison to identify failure in brittle and ductile mode and validate the developed method. Scratch testing results on mudrocks indicate that it is possible to use the recorded transverse force to estimate brittleness. Results show that tested samples rank as follows in increasing degree of brittleness: Woodford, Eagle Ford, Marcellus, Mancos, and Vaca Muerta. Eagle Ford samples show mixed ductile/brittle failure characteristics. There appears to be no definite correlation between micro-scratch brittleness and quartz or total carbonate content. Dolomite content shows a stronger correlation with brittleness than any other major mineral group. The scratch brittleness index correlates positively with increasing Young's modulus and decreasing Poisson's ratio, but shows deviations in rocks with distinct porosity and with stress-sensitive brittle/ductile behavior (Eagle Ford). The results of our study demonstrate that the micro-scratch test method can be used to investigate mudrock brittleness. The method is particularly useful for reservoir characterization methods that take advantage of drill cuttings or whenever large samples for triaxial testing or fracture mechanics testing cannot be recovered.

Seismic response of rock slopes: Numerical investigations on the role of internal structure

NASA Astrophysics Data System (ADS)

Arnold, L.; Applegate, K.; Gibson, M.; Wartman, J.; Adams, S.; Maclaughlin, M.; Smith, S.; Keefer, D. K.

2013-12-01

The stability of rock slopes is significantly influenced and often controlled by the internal structure of the slope created by such discontinuities as joints, shear zones, and faults. Under seismic conditions, these discontinuities influence both the resistance of a slope to failure and its response to dynamic loading. The dynamic response, which can be characterized by the slope's natural frequency and amplification of ground motion, governs the loading experienced by the slope in a seismic event and, therefore, influences the slope's stability. In support of the Network for Earthquake Engineering Simulation (NEES) project Seismically-Induced Rock Slope Failure: Mechanisms and Prediction (NEESROCK), we conducted a 2D numerical investigation using the discrete element method (DEM) coupled with simple discrete fracture networks (DFNs). The intact rock mass is simulated with a bonded assembly of discrete particles, commonly referred to as the bonded-particle model (BPM) for rock. Discontinuities in the BPM are formed by the insertion of smooth, unbonded contacts along specified planes. The influence of discontinuity spacing, orientation, and stiffness on slope natural frequency and amplification was investigated with the commercially available Particle Flow Code (PFC2D). Numerical results indicate that increased discontinuity spacing has a non-linear effect in decreasing the amplification and increasing the natural frequency of the slope. As discontinuity dip changes from sub-horizontal to sub-vertical, the slope's level of amplification increases while the natural frequency of the slope decreases. Increased joint stiffness decreases amplification and increases natural frequency. The results reveal that internal structure has a strong influence on rock slope dynamics that can significantly change the system's dynamic response and stability during seismic loading. Financial support for this research was provided by the United States National Science Foundation (NSF) under grant CMMI-1156413.

Challenges of constructing salt cavern gas storage in China

NASA Astrophysics Data System (ADS)

Xia, Yan; Yuan, Guangjie; Ban, Fansheng; Zhuang, Xiaoqian; Li, Jingcui

2017-11-01

After more than ten years of research and engineering practice in salt cavern gas storage, the engineering technology of geology, drilling, leaching, completion, operation and monitoring system has been established. With the rapid growth of domestic consumption of natural gas, the requirement of underground gas storage is increasing. Because high-quality rock salt resources about 1000m depth are relatively scarce, the salt cavern gas storages will be built in deep rock salt. According to the current domestic conventional construction technical scheme, construction in deep salt formations will face many problems such as circulating pressure increasing, tubing blockage, deformation failure, higher completion risk and so on, caused by depth and the complex geological conditions. Considering these difficulties, the differences between current technical scheme and the construction scheme of twin well and big hole are analyzed, and the results show that the technical scheme of twin well and big hole have obvious advantages in reducing the circulating pressure loss, tubing blockage and failure risk, and they can be the alternative schemes to solve the technical difficulties of constructing salt cavern gas storages in the deep rock salt.

Rockfall hazard assessment of nearly vertical rhyolite tuff cliff faces by using terrestrial laser scanner, UAV and FEM analyses

NASA Astrophysics Data System (ADS)

Török, Ákos; Barsi, Árpád; Görög, Péter; Lovas, Tamás; Bögöly, Gyula; Czinder, Balázs; Vásárhelyi, Balázs; Molnár, Bence; József Somogyi, Árpád

2017-04-01

Nearly vertical rhyolite tuff cliff faces are located in NE-Hungary representing rock fall hazard in the touristic region of Sirok. Larger blocks of the cliff have fallen in recent years menacing tourists and human lives. The rhyolite tuff, that forms the Castle Hill was formed during Miocene volcanism and comprises of brecciated lapilli tuffs and tuffs with intercalating ignimbritic horizons. The paper focuses on the 3D mapping of cliff faces and modeling of rock fall hazard. The topography and 3D model of the cliff was obtained by using GNSS supported terrestrial laser scanner and UAV. With imaging techniques of UAV a Triangulated Irregular Network (TIN) model was developed that contained triangles with 5-10 cm side lengths. GNSS supported terrestrial laser scanning allowed the observation with a resolution 1-5 cm of point spacing. The point clouds were further processed and with the combination of laser scanner and UAV data a 3D model of the studied cliff faces were obtained. Geological parameters for rock fall analyses included both field observations and laboratory tests. The lithotypes were identified on the field and were sampled for rock mechanical laboratory analyses. Joint- and fault system was mapped and visualized by using Rocscience Dip. EN test methods were used to obtain the density properties of various lithotypes of rhyolite tuff. Other standardized EN tests included ultrasonic pulse velocity, water absorption, indirect tensile strength (Brasilian), uniaxial compressive strength and modulus of elasticity of air dry and of water saturated samples. GSI values were denoted based on filed observations and rock mass properties. The stability analyses of cliff faces were made by using 2D FEM software (Phase 2). Cross sections were evaluated and global factor of safety was also calculated. The modeled displacements were in the order of few centimeters; however several locations were pinpointed where wedge failure and planar slip surfaces were identified as major cliff stability hazards. These were associated with the major joint systems dissecting cliff faces. This research have proved that the combined methods of field surveying, imaging techniques, data processing and FEM modelling with rock mechanical laboratory analyses allowed the identification of major rock fall hazards even at areas which are difficult to access.

GRAIN-SCALE FAILURE IN THERMAL SPALLATION DRILLING

DOE Office of Scientific and Technical Information (OSTI.GOV)

Walsh, S C; Lomov, I; Roberts, J J

2012-01-19

Geothermal power promises clean, renewable, reliable and potentially widely-available energy, but is limited by high initial capital costs. New drilling technologies are required to make geothermal power financially competitive with other energy sources. One potential solution is offered by Thermal Spallation Drilling (TSD) - a novel drilling technique in which small particles (spalls) are released from the rock surface by rapid heating. While TSD has the potential to improve drilling rates of brittle granitic rocks, the coupled thermomechanical processes involved in TSD are poorly described, making system control and optimization difficult for this drilling technology. In this paper, we discussmore » results from a new modeling effort investigating thermal spallation drilling. In particular, we describe an explicit model that simulates the grain-scale mechanics of thermal spallation and use this model to examine existing theories concerning spalling mechanisms. We will report how borehole conditions influence spall production, and discuss implications for macro-scale models of drilling systems.« less

Stratovolcano stability assessment methods and results from Citlaltepetl, Mexico

USGS Publications Warehouse

Zimbelman, D.R.; Watters, R.J.; Firth, I.R.; Breit, G.N.; Carrasco-Nunez, Gerardo

2004-01-01

Citlaltépetl volcano is the easternmost stratovolcano in the Trans-Mexican Volcanic Belt. Situated within 110 km of Veracruz, it has experienced two major collapse events and, subsequent to its last collapse, rebuilt a massive, symmetrical summit cone. To enhance hazard mitigation efforts we assess the stability of Citlaltépetl's summit cone, the area thought most likely to fail during a potential massive collapse event. Through geologic mapping, alteration mineralogy, geotechnical studies, and stability modeling we provide important constraints on the likelihood, location, and size of a potential collapse event. The volcano's summit cone is young, highly fractured, and hydrothermally altered. Fractures are most abundant within 5–20-m wide zones defined by multiple parallel to subparallel fractures. Alteration is most pervasive within the fracture systems and includes acid sulfate, advanced argillic, argillic, and silicification ranks. Fractured and altered rocks both have significantly reduced rock strengths, representing likely bounding surfaces for future collapse events. The fracture systems and altered rock masses occur non-uniformly, as an orthogonal set with N–S and E–W trends. Because these surfaces occur non-uniformly, hazards associated with collapse are unevenly distributed about the volcano. Depending on uncertainties in bounding surfaces, but constrained by detailed field studies, potential failure volumes are estimated to range between 0.04–0.5 km3. Stability modeling was used to assess potential edifice failure events. Modeled failure of the outer portion of the cone initially occurs as an "intact block" bounded by steeply dipping joints and outwardly dipping flow contacts. As collapse progresses, more of the inner cone fails and the outer "intact" block transforms into a collection of smaller blocks. Eventually, a steep face develops in the uppermost and central portion of the cone. This modeled failure morphology mimics collapse amphitheaters

A combined field/remote sensing approach for characterizing landslide risk in coastal areas

NASA Astrophysics Data System (ADS)

Francioni, Mirko; Coggan, John; Eyre, Matthew; Stead, Doug

2018-05-01

Understanding the key factors controlling slope failure mechanisms in coastal areas is the first and most important step for analyzing, reconstructing and predicting the scale, location and extent of future instability in rocky coastlines. Different failure mechanisms may be possible depending on the influence of the engineering properties of the rock mass (including the fracture network), the persistence and type of discontinuity and the relative aspect or orientation of the coastline. Using a section of the North Coast of Cornwall, UK, as an example we present a multi-disciplinary approach for characterizing landslide risk associated with coastal instabilities in a blocky rock mass. Remotely captured terrestrial and aerial LiDAR and photogrammetric data were interrogated using Geographic Information System (GIS) techniques to provide a framework for subsequent analysis, interpretation and validation. The remote sensing mapping data was used to define the rock mass discontinuity network of the area and to differentiate between major and minor geological structures controlling the evolution of the North Coast of Cornwall. Kinematic instability maps generated from aerial LiDAR data using GIS techniques and results from structural and engineering geological surveys are presented. With this method, it was possible to highlight the types of kinematic failure mechanism that may generate coastal landslides and highlight areas that are more susceptible to instability or increased risk of future instability. Multi-temporal aerial LiDAR data and orthophotos were also studied using GIS techniques to locate recent landslide failures, validate the results obtained from the kinematic instability maps through site observations and provide improved understanding of the factors controlling the coastal geomorphology. The approach adopted is not only useful for academic research, but also for local authorities and consultancy's when assessing the likely risks of coastal instability.

Geological constraints on the mechanism of tectonic tremor

NASA Astrophysics Data System (ADS)

Kirkpatrick, J. D.

2016-12-01

Observations of tectonic tremor in a wide variety of tectonic settings suggest that transitional behavior involving contemporaneous shear fracture and aseismic creep transients occurs in many major faults. Seismological and geophysical data indicate shear failure on critically stressed faults, likely under low effective stress conditions, are consistent characteristics, even though rock types and grain scale deformation mechanisms vary at these different locations. Geological observations could add additional insight into the specific failure mechanisms if the structures that form during tremor episodes can be identified. Exhumed shear zones often contain folded, boudinaged and/or dynamically recrystallized veins that record cyclical fracture and viscous deformation representing mixed bulk rheology. Examples from a Cretaceous transpressional continental shear zone in the Sierra Nevada, CA, include quartz-filled veins meters to tens of meters long with millimeters to centimeters of shear offset that preferentially developed along foliation planes in a high strain zone. Ambient temperatures during deformation were 400-600°C, and opening mode vein orientations and abundance suggest fluid pressure was near lithostatic at times. The orientation and spatial distribution of the veins indicate they formed under differential stress large enough for shear failure with pore pressures sufficiently high for the rocks to be critically stressed along mechanically weak foliation planes. Bulk deformation of the surrounding rock was accommodated viscously by crystal plastic deformation mechanisms. The mode of fracturing and overall behavior of the system was controlled by the local competition between the rates of stress recovery following fracture and stress drop, and pore pressure build up. The inferred mixed rheology recorded by the veins is phenomenologically similar to tremor. These shear fractures, and the conditions of failure they record, could be comparable to the mechanism that produces tectonic tremor.

Slope Stability Problems and Back Analysis in Heavily Jointed Rock Mass: A Case Study from Manisa, Turkey

NASA Astrophysics Data System (ADS)

Akin, Mutluhan

2013-03-01

This paper presents a case study regarding slope stability problems and the remedial slope stabilization work executed during the construction of two reinforced concrete water storage tanks on a steep hill in Manisa, Turkey. Water storage tanks of different capacities were planned to be constructed, one under the other, on closely jointed and deformed shale and sandstone units. The tank on the upper elevation was constructed first and an approximately 20-m cut slope with two benches was excavated in front of this upper tank before the construction of the lower tank. The cut slope failed after a week and the failure threatened the stability of the upper water tank. In addition to re-sloping, a 15.6-m deep contiguous retaining pile wall without anchoring was built to support both the cut slope and the upper tank. Despite the construction of a retaining pile wall, a maximum of 10 mm of displacement was observed by inclinometer measurements due to the re-failure of the slope on the existing slip surface. Permanent stability was achieved after the placement of a granular fill buttress on the slope. Back analysis based on the non-linear (Hoek-Brown) failure criterion indicated that the geological strength index (GSI) value of the slope-forming material is around 21 and is compatible with the in situ-determined GSI value (24). The calculated normal-shear stress plots are also consistent with the Hoek-Brown failure envelope of the rock mass, indicating that the location of the sliding surface, GSI value estimated by back analysis, and the rock mass parameters are well defined. The long-term stability analysis illustrates a safe slope design after the placement of a permanent toe buttress.

Monitoring and Early Warning of the 2012 Preonzo Catastrophic Rockslope Failure

NASA Astrophysics Data System (ADS)

Loew, Simon; Gschwind, Sophie; Keller-Signer, Alexandra; Valenti, Giorgio

2015-04-01

In this contribution we describe the accelerated creep stage and early warning system of a 210'000 m3 rock slope failure that occurred in May 2012 above the village of Preonzo (Swiss Alps). The very rapid failure occurred from a larger and retrogressive instability in high-grade metamorphic ortho-gneisses and amphibolites with a total volume of about 350'000 m3 located at an alpine meadow called Alpe di Roscioro. This instability showed clearly visible signs of movements since 1989 and accelerated creep with significant hydro-mechanical forcing since about 1999. Because the instability at Preonzo threatened a large industrial facility and important transport routes a cost-effective early warning system was installed in 2010. The alarm thresholds for pre-alarm, general public alarm and evacuation were derived from 10 years of continuous displacement monitoring with crack extensometers and an automated total station. These thresholds were successfully applied to evacuate the industrial facility and close important roads a few days before the catastrophic slope failure of May 15th, 2012. The rock slope failure occurred in two events, exposing a planar rupture plane dipping 42° and generating deposits in the mid-slope portion with a travel angle of 38°. Two hours after the second rockslide, the fresh colluvial deposits became reactivated in a devastating de-bris avalanche reaching the foot of the slope.

Eclogite-facies metamorphic reactions under stress and faulting in granulites from the Bergen Arcs, Norway: an experimental investigation

NASA Astrophysics Data System (ADS)

Incel, Sarah; Hilairet, Nadège; Labrousse, Loïc; Andersen, Torgeir B.; Wang, Yanbin; Schubnel, Alexandre

2017-04-01

Field observations from the Bergen Arcs, Norway, demonstrate a network of pseudotachylites quenched under eclogite-facies conditions in mafic granulites. In these nominally anhydrous high-pressure high-temperature (HP/HT) rocks the formation of pseudotachylites, believed to represent fossilized earthquakes, cannot be explained by processes akin to dehydration embrittlement. On the contrary, the transition to eclogite is expected to involve hydration of the initial rock. To experimentally investigate the underlying mechanisms leading to brittle failure in HP/HT rocks, we performed deformation experiments on natural granulite samples from the Bergen Arcs. The experiments were conducted under eclogite-facies conditions (2-3 GPa, 990-1220 K) to trigger the breakdown of plagioclase - the main constituent of granulite. For these experiments, both a D-DIA and a Griggs apparatus were used. The D-DIA press is mounted on a synchrotron beamline, enabling us to monitor strain, stress, and phase changes in-situ while contemporaneously recording acoustic emissions. The Griggs experiments were performed on a new device installed at ENS Paris, in which only stress-strain were recorded, and post-mortem microstructures investigated. The initial material consisted of a fine grain size granulite powder (< 38 µm) composed of mainly plagioclase and minor amount of pyroxene. Hydrous phases are phlogopite and epidote group minerals that make up less than 1 vol. % of the total bulk rock powder plus the adhesion water on grain surfaces. Mechanical data together with XRD observations and the record of acoustic emissions demonstrate a correlation between stress drops, the growth of plagioclase breakdown products and the onset of acoustic emissions during deformation of our specimen within the eclogitic field. Microstructural analysis show remarkable similarities with that of the natural ecoligitic pseudotachylites of the Bergen arcs. The plagioclase decomposition products form narrow conjugated shear bands, along which dissected and displaced crystals are found in the samples. The lack of microstructural evidence for macroscopic brittle failure in our microstructures could be due to plastic overprinting of early brittle structures. Nevertheless, our preliminary experimental results show a strong correlation between strain localization, dynamic fracture propagation (rapid enough to produce AEs) and the eclogitization of granulite.

Law on the Rocks: International Law and China’s Maritime Disputes

DTIC Science & Technology

2014-12-01

value .”258 Interpreting a rock as an island can entitle a coastal state to an additional 125,000 square nautical miles of exclusive economic zone...five patrol boats and an additional $18 million in assistance. Additionally , Vietnamese Defense Minister Gen. Phùng Quang Thanh extended an open...territory. Failure to defend what China perceives as national territory inspires maritime claimants to take more territory. Additionally , separatists in

Strain-dependent permeability of volcanic rocks.

NASA Astrophysics Data System (ADS)

Farquharson, Jamie; Heap, Michael; Baud, Patrick

2016-04-01

We explore permeability evolution during deformation of volcanic materials using a suite of rocks with varying compositions and physical properties (such as porosity ϕ). 40 mm × 20 mm cylindrical samples were made from a range of extrusive rocks, including andesites from Colima, Mexico (ϕ˜0.08; 0.18; 0.21), Kumamoto, Japan (ϕ˜0.13), and Ruapehu, New Zealand (ϕ˜0.15), and basalt from Mt Etna, Italy (ϕ˜0.04). Gas permeability of each sample was measured before and after triaxial deformation using a steady-state benchtop permeameter. To study the strain-dependence of permeability in volcanic rocks, we deformed samples to 2, 3, 4, 6, and 12 % axial strain at a constant strain rate of 10-5 s-1. Further, the influence of failure mode - dilatant or compactant - on permeability was assessed by repeating experiments at different confining pressures. During triaxial deformation, porosity change of the samples was monitored by a servo-controlled pore fluid pump. Below an initial porosity of ˜0.18, and at low confining pressures (≤ 20 MPa), we observe a dilatant failure mode (shear fracture formation). With increasing axial strain, stress is accommodated by fault sliding and the generation of ash-sized gouge between the fracture planes. In higher-porosity samples, or at relatively higher confining pressures (≥ 60 MPa), we observe compactant deformation characterised by a monotonous decrease in porosity with increasing axial strain. The relative permeability k' is given by the change in permeability divided by the initial reference state. When behaviour is dilatant, k' tends to be positive: permeability increases with progressive deformation. However, results suggest that after a threshold amount of strain, k' can decrease. k' always is negative (permeability decreases during deformation) when compaction is the dominant behaviour. Our results show that - in the absence of a sealing or healing process - the efficiency of a fault to transmit fluids is correlated to the degree of strain to which is subjected. Volcanic processes such as dome extrusion, which involve progressive strain on complex fault systems, have been seen to cause fault sliding and the prolific generation of fault gouge. Our results indicate that the permeability of these faults will tend to remain constant or increase during continued extrusion, allowing magmatic gases to readily outgas through permeable fault architectures despite the generation and accumulation of gouge. On the other hand, deeper regions of the edifice that will typically be compacting due to the relatively higher confining pressures, will exhibit a continuous decrease in permeability. The interplay between permeability-increasing and permeability-decreasing processes within the edifice is likely to influence outgassing and eruptive cycles at active volcanoes.

Global Assessment of Volcanic Debris Hazards from Space

NASA Technical Reports Server (NTRS)

Watters, Robert J.

2003-01-01

Hazard (slope stability) assessment for different sectors of volcano edifices was successfully obtained from volcanoes in North and South America. The assessment entailed Hyperion images to locate portions of the volcano that were hydrothermally altered to clay rich rocks with zones that were also rich in alunite and other minerals. The identified altered rock zones were field checked and sampled. The rock strength of these zones was calculated from the field and laboratory measurements. Volcano modeling utilizing the distinct element method and limit equilibrium technique, with the calculated strength data was used to assess stability and deformation of the edifice. Modeling results give indications of possible failure volumes, velocities and direction. The models show the crucial role hydrothermally weak rock plays in reducing the strength o the volcano edifice and the rapid identification of weak rock through remote sensing techniques. Volcanoes were assessed in the Cascade Range (USA), Mexico, and Chile (ongoing).

Rock Fracture Toughness Study Under Mixed Mode I/III Loading

NASA Astrophysics Data System (ADS)

Aliha, M. R. M.; Bahmani, A.

2017-07-01

Fracture growth in underground rock structures occurs under complex stress states, which typically include the in- and out-of-plane sliding deformation of jointed rock masses before catastrophic failure. However, the lack of a comprehensive theoretical and experimental fracture toughness study for rocks under contributions of out-of plane deformations (i.e. mode III) is one of the shortcomings of this field. Therefore, in this research the mixed mode I/III fracture toughness of a typical rock material is investigated experimentally by means of a novel cracked disc specimen subjected to bend loading. It was shown that the specimen can provide full combinations of modes I and III and consequently a complete set of mixed mode I/III fracture toughness data were determined for the tested marble rock. By moving from pure mode I towards pure mode III, fracture load was increased; however, the corresponding fracture toughness value became smaller. The obtained experimental fracture toughness results were finally predicted using theoretical and empirical fracture models.

Practical example of the infrastructure protection against rock fall

NASA Astrophysics Data System (ADS)

Jirásko, Daniel; Vaníček, Ivan

2017-09-01

The protection of transport infrastructures against rock falls represents for the Czech Republic one of the sensitive questions. Rock falls, similarly as other typical geo-hazards for the Czech Republic, as landslides and floods, can have negative impact on safety and security of these infrastructures. One practical example how to reduce risk of rock fall is described in the paper. Great care is devoted to the visual inspection enabling to indicate places with high potential to failure. With the help of numerical modelling the range of rock fall negative impact is estimated. Protection measures are dealing with two basic ways. The first one utilize the results of numerical modelling for the optimal design of protection measures and the second one is focused on the monitoring of the rock blocks with high potential of instability together with wire-less transfer of measured results. After quick evaluation, e.g. comparison with warning values, some protection measures, mostly connected with closure of the potential sector, can be recommended.

Study of deformation evolution during failure of rock specimens using laser-based vibration measurements

NASA Astrophysics Data System (ADS)

Smolin, I. Yu.; Kulkov, A. S.; Makarov, P. V.; Tunda, V. A.; Krasnoveikin, V. A.; Eremin, M. O.; Bakeev, R. A.

2017-12-01

The aim of the paper is to analyze experimental data on the dynamic response of the marble specimen in uniaxial compression. To make it we use the methods of mathematical statistics. The lateral surface velocity evolution obtained by the laser Doppler vibrometer represents the data for analysis. The registered data were regarded as a time series that reflects deformation evolution of the specimen loaded up to failure. The revealed changes in statistical parameters were considered as precursors of failure. It is shown that before failure the deformation response is autocorrelated and reflects the states of dynamic chaos and self-organized criticality.

Deeply subducted continental fragments - Part 1: Fracturing, dissolution-precipitation, and diffusion processes recorded by garnet textures of the central Sesia Zone (western Italian Alps)

NASA Astrophysics Data System (ADS)

Giuntoli, Francesco; Lanari, Pierre; Engi, Martin

2018-02-01

Contiguous continental high-pressure terranes in orogens offer insight into deep recycling and transformation processes that occur in subduction zones. These remain poorly understood, and currently debated ideas need testing. The approach we chose is to investigate, in detail, the record in suitable rock samples that preserve textures and robust mineral assemblages that withstood overprinting during exhumation. We document complex garnet zoning in eclogitic mica schists from the Sesia Zone (western Italian Alps). These retain evidence of two orogenic cycles and provide detailed insight into resorption, growth, and diffusion processes induced by fluid pulses in high-pressure conditions. We analysed local textures and garnet compositional patterns, which turned out remarkably complex. By combining these with thermodynamic modelling, we could unravel and quantify repeated fluid-rock interaction processes. Garnet shows low-Ca porphyroclastic cores that were stable under (Permian) granulite facies conditions. The series of rims that surround these cores provide insight into the subsequent evolution: the first garnet rim that surrounds the pre-Alpine granulite facies core in one sample indicates that pre-Alpine amphibolite facies metamorphism followed the granulite facies event. In all samples documented, cores show lobate edges and preserve inner fractures, which are sealed by high-Ca garnet that reflects high-pressure Alpine conditions. These observations suggest that during early stages of subduction, before hydration of the granulites, brittle failure of garnet occurred, indicating high strain rates that may be due to seismic failure. Several Alpine rims show conspicuous textures indicative of interaction with hydrous fluid: (a) resorption-dominated textures produced lobate edges, at the expense of the outer part of the granulite core; (b) peninsulas and atoll garnet are the result of replacement reactions; and (c) spatially limited resorption and enhanced transport of elements due to the fluid phase are evident along brittle fractures and in their immediate proximity. Thermodynamic modelling shows that all of these Alpine rims formed under eclogite facies conditions. Structurally controlled samples allow these fluid-garnet interaction phenomena to be traced across a portion of the Sesia Zone, with a general decrease in fluid-garnet interaction observed towards the external, structurally lower parts of the terrane. Replacement of the Permian HT assemblages by hydrate-rich Alpine assemblages can reach nearly 100 % of the rock volume. Since we found no clear relationship between discrete deformation structures (e.g. shear zones) observed in the field and the fluid pulses that triggered the transformation to eclogite facies assemblages, we conclude that disperse fluid flow was responsible for the hydration.

Time-Dependent Damage Investigation of Rock Mass in an In Situ Experimental Tunnel

PubMed Central

Jiang, Quan; Cui, Jie; Chen, Jing

2012-01-01

In underground tunnels or caverns, time-dependent deformation or failure of rock mass, such as extending cracks, gradual rock falls, etc., are a costly irritant and a major safety concern if the time-dependent damage of surrounding rock is serious. To understand the damage evolution of rock mass in underground engineering, an in situ experimental testing was carried out in a large belowground tunnel with a scale of 28.5 m in width, 21 m in height and 352 m in length. The time-dependent damage of rock mass was detected in succession by an ultrasonic wave test after excavation. The testing results showed that the time-dependent damage of rock mass could last a long time, i.e., nearly 30 days. Regression analysis of damage factors defined by wave velocity, resulted in the time-dependent evolutional damage equation of rock mass, which corresponded with logarithmic format. A damage viscoelastic-plastic model was developed to describe the exposed time-dependent deterioration of rock mass by field test, such as convergence of time-dependent damage, deterioration of elastic modules and logarithmic format of damage factor. Furthermore, the remedial measures for damaged surrounding rock were discussed based on the measured results and the conception of damage compensation, which provides new clues for underground engineering design.

Rust and schreibersite in Apollo 16 highland rocks - Manifestations of volatile-element mobility

NASA Technical Reports Server (NTRS)

Hunter, R. H.; Taylor, L. A.

1982-01-01

Rust is a manifestation of halogen and volatile-metal mobility in the lunar environment. Schreibersite is stable as the primary phosphorus-bearing phase in the highland rocks, a consequence of the inherently low oxygen fugacity within impact-generated melts. Apatite and whitlockite are subordinate in these rocks. The partitioning of P into phosphide in impact-generated melts, and the failure of phosphate to crystallize, effects a decoupling of the halogens and phosphorus. Of the Apollo 16 rocks, 63% contain rust, 70% contain schreibersite, and 52% contain both phases, thereby establishing the pervasiveness of volatile-elements throughout the highland rocks. The major portion of these volatile-bearing phases occur in impact melt-rocks or in breccia matrices. Rhabdites of schreibersite in some of the FeNi grains indicate that there is a meteoritic contribution to the phosphorus in these rocks. Cl/P2O5 ratios in lunar highland rocks are a function of secondary effects, with any apparent Cl-P correlations being coincidential. The present observations preclude the validity of models based on such elemental ratios in these rocks. The presence of rust in the clast laden matrices of pristine rocks indicates fugitive element localization. Pristine clasts may have been contaminated. The basis for a pristine volatile chemistry is questioned.

Relating triggering processes in lab experiments with earthquakes.

NASA Astrophysics Data System (ADS)

Baro Urbea, J.; Davidsen, J.; Kwiatek, G.; Charalampidou, E. M.; Goebel, T.; Stanchits, S. A.; Vives, E.; Dresen, G.

2016-12-01

Statistical relations such as Gutenberg-Richter's, Omori-Utsu's and the productivity of aftershocks were first observed in seismology, but are also common to other physical phenomena exhibiting avalanche dynamics such as solar flares, rock fracture, structural phase transitions and even stock market transactions. All these examples exhibit spatio-temporal correlations that can be explained as triggering processes: Instead of being activated as a response to external driving or fluctuations, some events are consequence of previous activity. Although different plausible explanations have been suggested in each system, the ubiquity of such statistical laws remains unknown. However, the case of rock fracture may exhibit a physical connection with seismology. It has been suggested that some features of seismology have a microscopic origin and are reproducible over a vast range of scales. This hypothesis has motivated mechanical experiments to generate artificial catalogues of earthquakes at a laboratory scale -so called labquakes- and under controlled conditions. Microscopic fractures in lab tests release elastic waves that are recorded as ultrasonic (kHz-MHz) acoustic emission (AE) events by means of piezoelectric transducers. Here, we analyse the statistics of labquakes recorded during the failure of small samples of natural rocks and artificial porous materials under different controlled compression regimes. Temporal and spatio-temporal correlations are identified in certain cases. Specifically, we distinguish between the background and triggered events, revealing some differences in the statistical properties. We fit the data to statistical models of seismicity. As a particular case, we explore the branching process approach simplified in the Epidemic Type Aftershock Sequence (ETAS) model. We evaluate the empirical spatio-temporal kernel of the model and investigate the physical origins of triggering. Our analysis of the focal mechanisms implies that the occurrence of the empirical laws extends well beyond purely frictional sliding events, in contrast to what is often assumed.

Numerical Analyses of the Influence of Blast-Induced Damaged Rock Around Shallow Tunnels in Brittle Rock

NASA Astrophysics Data System (ADS)

Saiang, David; Nordlund, Erling

2009-06-01

Most of the railway tunnels in Sweden are shallow-seated (<20 m of rock cover) and are located in hard brittle rock masses. The majority of these tunnels are excavated by drilling and blasting, which, consequently, result in the development of a blast-induced damaged zone around the tunnel boundary. Theoretically, the presence of this zone, with its reduced strength and stiffness, will affect the overall performance of the tunnel, as well as its construction and maintenance. The Swedish Railroad Administration, therefore, uses a set of guidelines based on peak particle velocity models and perimeter blasting to regulate the extent of damage due to blasting. However, the real effects of the damage caused by blasting around a shallow tunnel and their criticality to the overall performance of the tunnel are yet to be quantified and, therefore, remain the subject of research and investigation. This paper presents a numerical parametric study of blast-induced damage in rock. By varying the strength and stiffness of the blast-induced damaged zone and other relevant parameters, the near-field rock mass response was evaluated in terms of the effects on induced boundary stresses and ground deformation. The continuum method of numerical analysis was used. The input parameters, particularly those relating to strength and stiffness, were estimated using a systematic approach related to the fact that, at shallow depths, the stress and geologic conditions may be highly anisotropic. Due to the lack of data on the post-failure characteristics of the rock mass, the traditional Mohr-Coulomb yield criterion was assumed and used. The results clearly indicate that, as expected, the presence of the blast-induced damage zone does affect the behaviour of the boundary stresses and ground deformation. Potential failure types occurring around the tunnel boundary and their mechanisms have also been identified.

Characterization of Unstable Rock Slopes Through Passive Seismic Measurements

NASA Astrophysics Data System (ADS)

Kleinbrod, Ulrike; Burjánek, Jan; Fäh, Donat

2014-05-01

Catastrophic rock slope failures have high social impact, causing significant damage to infrastructure and many casualties throughout the world each year. Both detection and characterization of rock instabilities are therefore of key importance. Analysing unstable rock slopes by means of ambient vibrations might be a new alternative to the already existing methods as for example geotechnical displacement measurements. A systematic measurement campaign has been initiated recently in Switzerland in order to study the seismic response of potential rockslides concerning a broad class of slope failure mechanisms and material conditions. First results are presented in this contribution. Small aperture seismic arrays were deployed at sites of interest for a short period of time (several hours) in order to record ambient vibrations. During each measurement a reference station was installed on a stable part close to the instability. The total number of stations used varies from 16 down to 2, depending on the site scope and resource availability. Instable rock slopes show a highly directional ground motion which is significantly amplified with respect to stable areas. These effects are strongest at certain frequencies which are identified as eigenfrequencies of the unstable rock mass. The eigenfrequencies and predominant directions have been estimated by frequency dependent polarization analysis. Site-to-reference spectral ratios have been calculated as well in order to estimate the relative amplification of ground motion at unstable parts. The retrieved results were compared with independent in-situ observations and other available data. The directions of maximum amplification are in most cases perpendicular to open cracks mapped on the surface and in good agreement with the deformation directions obtained by geodetic measurements. The interpretation of the observed wave field is done through numerical modelling of seismic wave propagation in fractured media with complex topography. For example, a potential relation between eigenfrequencies and unstable rock mass volume is investigated.

Hayward Fault rocks: porosity, density, and strength measurements

USGS Publications Warehouse

Morrow, C.A.; Lockner, D.A.

2001-01-01

Porosity, density and strength measurements were conducted on rock samples collected from the Hayward Fault region in Northern California as part of the Hayward Fault Working Group’s efforts to create a working model of the Hayward Fault. The rocks included in this study were both fine and coarse grained gabbros, altered keratophyre, basalt, sandstone, and serpentinite from various rock formations adjacent to the Hayward Fault. Densities ranged from a low of 2.25 gm/cc (altered keratophyre) to 3.05 gm/cc (fine gabbro), with an average of 2.6 gm/cc, typical of many other rocks. Porosities were generally around 1% or less, with the exception of the sandstone (7.6%) and altered keratophyre (13.5%). Failure and frictional sliding tests were conducted on intact rock cylinders at room temperature under effective pressure conditions of up to 192 MPa, simulating depths of burial to 12 km. Axial shortening of the samples progressed at a rate of 0.1 µm/sec (fine samples) or 0.2 µm/sec (porous samples) for 6 mm of displacement. Velocity stepping tests were then conducted for an additional 2 mm of displacement, for a total of 8 mm. Both peak strength (usually failure strength) and frictional strength, determined at 8 mm of displacement, increased systematically with effective pressure. Coefficients of friction, based on the observed fracture angles, ranged from 0.6 to 0.85, consistent with Byerlee’s Law. Possible secondary influences on the strength of the Hayward rock samples may be surface weathering, or a larger number of pre-existing fractures due to the proximity to the Hayward Fault. All samples showed velocity strengthening, so that the average a-b values were all strongly positive. There was no systematic relation between a-b values and effective pressure. Velocity strengthening behavior is associated with stable sliding (creep), as observed in the shallow portions of the Hayward Fault.

Data Validation Package September 2016 Groundwater and Surface Water Sampling at the Slick Rock, Colorado, Processing Sites January 2017

DOE Office of Scientific and Technical Information (OSTI.GOV)

Traub, David; Nguyen, Jason

The Slick Rock, Colorado, Processing Sites are referred to as the Slick Rock West Processing Site (SRK05) and the Slick Rock East Processing Site (SRK06). This annual event involved sampling both sites for a total of 16 monitoring wells and 6 surface water locations as required by the 2006 Draft Final Ground Water Compliance Action Plan for the Slick Rock, Colorado, Processing Sites (GCAP). A domestic well was also sampled at a property adjacent to the Slick Rock East site at the request of the landowner.

Large-scale mechanical buckle fold development and the initiation of tensile fractures

NASA Astrophysics Data System (ADS)

Eckert, Andreas; Connolly, Peter; Liu, Xiaolong

2014-11-01

failure associated with buckle folding is commonly associated to the distribution of outer arc extension but has also been observed on fold limbs. This study investigates whether tensile stresses and associated failure can be explained by the process of buckling under realistic in situ stress conditions. A 2-D plane strain finite element modeling approach is used to study single-layer buckle folds with a Maxwell viscoelastic rheology. A variety of material parameters are considered and their influence on the initiation of tensile stresses during the various stages of deformation is analyzed. It is concluded that the buckling process determines the strain distribution within the fold layer but is not solely responsible for the initiation of tensile stresses. The modeling results show that tensile stresses are most dependent on the permeability, viscosity, and overburden thickness. Low permeability (<10-19 m2), high viscosity (≥1021 Pa s), and low overburden pressure can explain tensile failure at the fold hinge. Tensile stresses in the limb of the fold cannot (in general) be explained by buckling. Rather, it develops due to a combination of compression and erosional unloading. The modeling results show that erosion of high permeability rocks can explain the generation of tensile stresses at significant depths (˜2 km) both at the hinge of the fold and throughout the limb of the fold. This study shows that tensile stresses and associated failure within buckle folds is directly dependent on the distribution of material parameters but moreover to the strain history of the geologic system.

Earthquake and failure forecasting in real-time: A Forecasting Model Testing Centre

NASA Astrophysics Data System (ADS)

Filgueira, Rosa; Atkinson, Malcolm; Bell, Andrew; Main, Ian; Boon, Steven; Meredith, Philip

2013-04-01

Across Europe there are a large number of rock deformation laboratories, each of which runs many experiments. Similarly there are a large number of theoretical rock physicists who develop constitutive and computational models both for rock deformation and changes in geophysical properties. Here we consider how to open up opportunities for sharing experimental data in a way that is integrated with multiple hypothesis testing. We present a prototype for a new forecasting model testing centre based on e-infrastructures for capturing and sharing data and models to accelerate the Rock Physicist (RP) research. This proposal is triggered by our work on data assimilation in the NERC EFFORT (Earthquake and Failure Forecasting in Real Time) project, using data provided by the NERC CREEP 2 experimental project as a test case. EFFORT is a multi-disciplinary collaboration between Geoscientists, Rock Physicists and Computer Scientist. Brittle failure of the crust is likely to play a key role in controlling the timing of a range of geophysical hazards, such as volcanic eruptions, yet the predictability of brittle failure is unknown. Our aim is to provide a facility for developing and testing models to forecast brittle failure in experimental and natural data. Model testing is performed in real-time, verifiably prospective mode, in order to avoid selection biases that are possible in retrospective analyses. The project will ultimately quantify the predictability of brittle failure, and how this predictability scales from simple, controlled laboratory conditions to the complex, uncontrolled real world. Experimental data are collected from controlled laboratory experiments which includes data from the UCL Laboratory and from Creep2 project which will undertake experiments in a deep-sea laboratory. We illustrate the properties of the prototype testing centre by streaming and analysing realistically noisy synthetic data, as an aid to generating and improving testing methodologies in imperfect conditions. The forecasting model testing centre uses a repository to hold all the data and models and a catalogue to hold all the corresponding metadata. It allows to: Data transfer: Upload experimental data: We have developed FAST (Flexible Automated Streaming Transfer) tool to upload data from RP laboratories to the repository. FAST sets up data transfer requirements and selects automatically the transfer protocol. Metadata are automatically created and stored. Web data access: Create synthetic data: Users can choose a generator and supply parameters. Synthetic data are automatically stored with corresponding metadata. Select data and models: Search the metadata using criteria design for RP. The metadata of each data (synthetic or from laboratory) and models are well-described through their respective catalogues accessible by the web portal. Upload models: Upload and store a model with associated metadata. This provide an opportunity to share models. The web portal solicits and creates metadata describing each model. Run model and visualise results: Selected data and a model to be submitted to a High Performance Computational resource hiding technical details. Results are displayed in accelerated time and stored allowing retrieval, inspection and aggregation. The forecasting model testing centre proposed could be integrated into EPOS. Its expected benefits are: Improved the understanding of brittle failure prediction and its scalability to natural phenomena. Accelerated and extensive testing and rapid sharing of insights. Increased impact and visibility of RP and GeoScience research. Resources for education and training. A key challenge is to agree the framework for sharing RP data and models. Our work is provocative first step.

Rock riprap design for protection of stream channels near highway structures; Volume 2, Evaluation of Riprap design procedures

USGS Publications Warehouse

Blodgett, J.C.; McConaughy, C.E.

1986-01-01

In volume 2, seven procedures now being used for design of rock riprap installations were evaluated using data from 26 field sites. Four basic types of riprap failures were identified: Particle erosion, translational slide, modified slump, and slump. Factors associated with riprap failure include stone size , bank side slope, size gradation, thickness, insufficient toe or endwall, failure of the bank material, overtopping during floods, and geomorphic changes in the channel. A review of field data and the design procedures suggests that estimates of hydraulic forces acting on the boundary based on flow velocity rather than shear stress are more reliable. Several adjustments for local conditions, such as channel curvature, superelevation, or boundary roughness, may be unwarranted in view of the difficulty in estimating critical hydraulic forces for which the riprap is to be designed. Success of the riprap is related not only to the appropriate procedure for selecting stone size, but also to the reliability of estimated hydraulic and channel factors applicable to the site. (See also W89-04910) (Author 's abstract)

Dynamic tensile-failure-induced velocity deficits in rock

NASA Technical Reports Server (NTRS)

Rubin, Allan M.; Ahrens, Thomas J.

1991-01-01

Planar impact experiments were employed to induce dynamic tensile failure in Bedford limestone. Rock disks were impacted with aluminum and polymethyl methacralate (PMMA) flyer plates at velocities of 10 to 25 m/s. Tensile stress magnitudes and duration were chosen so as to induce a range of microcrack growth insufficient to cause complete spalling of the samples. Ultrasonic P- and S-wave velocities of recovered targets were compared to the velocities prior to impact. Velocity reduction, and by inference microcrack production, occurred in samples subjected to stresses above 35 MPa in the 1.3 microsec PMMA experiments and 60 MPa in the 0.5 microsec aluminum experiments. Using a simple model for the time-dependent stress-intensity factor at the tips of existing flaws, apparent fracture toughnesses of 2.4 and 2.5 MPa sq rt m are computed for the 1.3 and 0.5 microsec experiments. These are a factor of about 2 to 3 greater than quasi-static values. The greater dynamic fracture toughness observed may result from microcrack interaction during tensile failure. Data for water-saturated and dry targets are indistinguishable.

Analysis of EDZ Development of Columnar Jointed Rock Mass in the Baihetan Diversion Tunnel

NASA Astrophysics Data System (ADS)

Hao, Xian-Jie; Feng, Xia-Ting; Yang, Cheng-Xiang; Jiang, Quan; Li, Shao-Jun

2016-04-01

Due to the time dependency of the crack propagation, columnar jointed rock masses exhibit marked time-dependent behaviour. In this study, in situ measurements, scanning electron microscope (SEM), back-analysis method and numerical simulations are presented to study the time-dependent development of the excavation damaged zone (EDZ) around underground diversion tunnels in a columnar jointed rock mass. Through in situ measurements of crack propagation and EDZ development, their extent is seen to have increased over time, despite the fact that the advancing face has passed. Similar to creep behaviour, the time-dependent EDZ development curve also consists of three stages: a deceleration stage, a stabilization stage, and an acceleration stage. A corresponding constitutive model of columnar jointed rock mass considering time-dependent behaviour is proposed. The time-dependent degradation coefficient of the roughness coefficient and residual friction angle in the Barton-Bandis strength criterion are taken into account. An intelligent back-analysis method is adopted to obtain the unknown time-dependent degradation coefficients for the proposed constitutive model. The numerical modelling results are in good agreement with the measured EDZ. Not only that, the failure pattern simulated by this time-dependent constitutive model is consistent with that observed in the scanning electron microscope (SEM) and in situ observation, indicating that this model could accurately simulate the failure pattern and time-dependent EDZ development of columnar joints. Moreover, the effects of the support system provided and the in situ stress on the time-dependent coefficients are studied. Finally, the long-term stability analysis of diversion tunnels excavated in columnar jointed rock masses is performed.

Himalayan Sackung and Associations to Regional Structure

NASA Astrophysics Data System (ADS)

Shroder, J. F.; Bishop, M. P.; Olsenholler, J.

2003-12-01

Recognition of sackung slope failure or deep-seated, rock-slope deformation in the Himalaya has been rather limited, in part because: (1) many geoscientists do not recognize its characteristics; (2) large-scale aerial photographs and topographic maps used to identify the characteristic surficial, topographic manifestations of the failure type are commonly low-level state secrets in that region; and (3) no systematic survey for sackung has ever been made in the Himalaya. In the Pakistani-controlled, western Himalaya, some unconventional access to aerial photographs in the Kaghan and Nanga Parbat areas allowed first recognition of several characteristic ridge-top grabens and anti-slope scarps. Later release of declassified, stereo imagery from the CORONA and KEYHOLE satellite series enabled discovery of other examples in the K2 region. Comparison of mapped sackung failures with geologic base maps has demonstrated some coincidence of sackung with various structural trends, including synformal structures in upper thrust plates or along the traces of high-angle faults. In all probability these structural trends have provided plentiful ancillary planes of weakness along which gravitationally driven sackung is facilitated. Sackung failure in the Himalaya appears to be a spatially scale-dependent manifestation of a gravitational-collapse continuum of the brittle, upper crust, mainly involving mountain ridges. In contrast, gravitational collapse of the whole range may involve some similar failures but also include listric faulting, as well as subsidence movement into zones of ductility at depth. Temporal scale dependence of sackung may also be threshold dominated, wherein initial long-continued, slow failure ultimately leads to the commonly catastrophic rock-slope collapses recently recognized throughout the western Himalaya and now differentiated from their original mismapping as glacial moraines. Such sackung in Himalayan terrain undergoing active deglaciation from global warming may increase catastrophic slope-failure hazard.

Standardization of mapping practices in the British Geological Survey

NASA Astrophysics Data System (ADS)

Allen, Peter M.

1997-07-01

Because the British Geological Survey (BGS) has had, since its foundation in 1835, a mandate to produce geological maps for the whole of Great Britain, there is a long history of introducing standard practices in the way rocks and rock units have been named, classified and illustrated on maps. The reasons for the failure of some of these practices are examined and assessed in relation to the needs of computerized systems for holding and disseminating geological information.

The furnace in the basement: Part 1, The early days of the Hot Dry Rock Geothermal Energy Program, 1970--1973

DOE Office of Scientific and Technical Information (OSTI.GOV)

Smith, M.C.

1995-09-01

This report presents the descriptions of the background information and formation of the Los Alamos Scientific Laboratory Geothermal Energy Group. It discusses the organizational, financial, political, public-relations,geologic, hydrologic, physical, and mechanical problems encountered by the group during the period 1970--1973. It reports the failures as well as the successes of this essential first stage in the development of hot dry rock geothermal energy systems.

Deformation modes in an Icelandic basalt: From brittle failure to localized deformation bands

NASA Astrophysics Data System (ADS)

Adelinet, M.; Fortin, J.; Schubnel, A.; Guéguen, Y.

2013-04-01

According to the stress state, deformation mode observed in rocks may be very different. Even in the brittle part of the crust a differential stress can induce shear failure but also localized compacting deformation, such as compaction bands in porous sedimentary rocks. The mode of deformation controls many hydrodynamic factors, such as permeability and porosity. We investigate in this paper two different modes of deformation in an Icelandic basalt by using laboratory seismological tools (elastic waves and acoustic emissions) and microstructural observations. First of all, we show that at low effective confining pressure (Peff = 5 MPa) an axial loading induces a shear failure in the basalt with an angle of about 30° with respect to the main stress direction. On the contrary, at high effective confining pressure (Peff ≥ 75 MPa and more) an increase of the axial stress induces a localization of the deformation in the form of subhorizontal bands again with respect to the main stress direction. In this second regime, focal mechanisms of the acoustic emissions reveal an important number of compression events suggesting pore collapse mechanisms. Microstructural observations confirm this assumption. Similar compaction structures are usually obtained for porous sedimentary rocks (20-25%). However, the investigated basalt has an initial total porosity of only about 10% so that compaction structures were not expected. The pore size and the ratio of pore to grain size are likely to be key factors for the particular observed mechanical behavior.

Increasing rock-avalanche frequency correlates with increasing seismic moment release in New Zealand's Southern Alps

NASA Astrophysics Data System (ADS)

McSaveney, Mauri; Cox, Simon; Hancox, Graham

2015-04-01

The occurrence rate of large, spontaneous rock avalanches in New Zealand's Southern Alps has increasing over the last 50 years. The rate has been about 20 events per decade for the last 10 years, whereas for the period 1976-1999, it was 4 per decade. Allen et al. 2011 and Allen and Huggel, 2013 link the increase to alpine permafrost decay due to anthropogenic global warming, similar to the increased occurrence rate in the European Alps which is attributed to this cause. We however suggest a different primary cause, linking the increase to tectonic strain, which has been shown to also affect valley-bottom hot springs in the region. The altitudes from which these landslides have fallen are coincident with the region's topographically protruding slopes which favour stress concentration and failure, and many, but not all, failures have been from already highly fractured rock masses, for which an explanation of the fracturing is called for. Also, the earliest documented spontaneous rock avalanche in the Southern Alps occurred in 1873 and fell from a similar altitude on the same face of the same mountain as the most recent event in 2014. Cox et al. (2014) shows that valley-bottom hot springs in the Southern Alps respond to distant strong earthquakes in a manner suggesting weak local ground deformation and increased bedrock permeability. We suggest that the surrounding slopes respond to the same stimuli. We find that the observed occurrence-rate increase has occurred simultaneously with a seismic-moment-release increase in New Zealand, which follows the trend of global seismic moment release. It may also be associated with the accumulating slope deformations since about 1717 AD, when a great earthquake triggered much slope collapse in the region. In support of this link, Barff (1873) which reports the 1873 landslide from Aoraki/Mount Cook, also reports a seemingly associated but unexplained shift of hot springs in the area. The timing of both coincides with a distant series of moderate earthquakes west of North Island, New Zealand, which was felt widely in North Island. The New Zealand seismological record is complete enough since 1969 for earthquake magnitudes ≥4.0 to enable determination of seismic moment release. We applied an exponential distance attenuation to the accumulating moment release with an empirical decay constant of 2093 km to obtain closely matching trends between our two data sets. Such a relatively slow decay with distance may imply that ong-wavelength surface waves are affecting the slopes. On the other hand, the increasing landslide frequency sometimes leads the increasing seismic moment, suggesting that the two may be driven by a third process such as accumulating regional crustal strain in the South Pacific. An earthquake of M>8.0 occurred over 290 years ago (ca. 1717 AD) on the Alpine fault with no major release of regional crustal strain there since that time. This earthquake is expected to have triggered widespread landsliding in the central Southern Alps. Since that regional release of elastic crustal strain, the underlying rock mass of the S. Alps has been accumulating elastic strain beneath a relatively thin skin of semi-detached, brittle and closely jointed rock. The estimated mean recurrence time of ruptures on the Alpine fault is about 330 years, and so, the expected misfits between the deforming intact rock and the overlying dilated granular masses of potential landslides can be expected to be approaching average levels not present since before 1717 AD. Perhaps this is the reason why more of the semi-detached masses are completing the detachment process and falling off. We do not discount an additional link with permafrost decay, which is a mechanism with potential to lower the cohesion in granular rock masses in the permafrost zone of the higher Southern Alps. But permafrost decay does not create granular rock masses.

High Resolution Rapid Revisits Insar Monitoring of Surface Deformation

NASA Astrophysics Data System (ADS)

Singhroy, V.; Li, J.; Charbonneau, F.

2014-12-01

Monitoring surface deformation on strategic energy and transportation corridors requires high resolution spatial and temporal InSAR images for mitigation and safety purposes. High resolution air photos, lidar and other satellite images are very useful in areas where the landslides can be fatal. Recently, radar interferometry (InSAR) techniques using more rapid revisit images from several radar satellites are increasingly being used in active deformation monitoring. The Canadian RADARSAT Constellation (RCM) is a three-satellite mission that will provide rapid revisits of four days interferometric (InSAR) capabilities that will be very useful for complex deformation monitoring. For instance, the monitoring of surface deformation due to permafrost activity, complex rock slide motion and steam assisted oil extraction will benefit from this new rapid revisit capability. This paper provide examples of how the high resolution (1-3 m) rapid revisit InSAR capabilities will improve our monitoring of surface deformation and provide insights in understanding triggering mechanisms. We analysed over a hundred high resolution InSAR images over a two year period on three geologically different sites with various configurations of topography, geomorphology, and geology conditions. We show from our analysis that the more frequent InSAR acquisitions are providing more information in understanding the rates of movement and failure process of permafrost triggered retrogressive thaw flows; the complex motion of an asymmetrical wedge failure of an active rock slide and the identification of over pressure zones related to oil extraction using steam injection. Keywords: High resolution, InSAR, rapid revisits, triggering mechanisms, oil extraction.

Rockfall hazard assessment integrating probabilistic physically based rockfall source detection (Norddal municipality, Norway).

NASA Astrophysics Data System (ADS)

Yugsi Molina, F. X.; Oppikofer, T.; Fischer, L.; Hermanns, R. L.; Taurisano, A.

2012-04-01

Traditional techniques to assess rockfall hazard are partially based on probabilistic analysis. Stochastic methods has been used for run-out analysis of rock blocks to estimate the trajectories that a detached block will follow during its fall until it stops due to kinetic energy loss. However, the selection of rockfall source areas is usually defined either by multivariate analysis or by field observations. For either case, a physically based approach is not used for the source area detection. We present an example of rockfall hazard assessment that integrates a probabilistic rockfall run-out analysis with a stochastic assessment of the rockfall source areas using kinematic stability analysis in a GIS environment. The method has been tested for a steep more than 200 m high rock wall, located in the municipality of Norddal (Møre og Romsdal county, Norway), where a large number of people are either exposed to snow avalanches, rockfalls, or debris flows. The area was selected following the recently published hazard mapping plan of Norway. The cliff is formed by medium to coarse-grained quartz-dioritic to granitic gneisses of Proterozoic age. Scree deposits product of recent rockfall activity are found at the bottom of the rock wall. Large blocks can be found several tens of meters away from the cliff in Sylte, the main locality in the Norddal municipality. Structural characterization of the rock wall was done using terrestrial laser scanning (TLS) point clouds in the software Coltop3D (www.terranum.ch), and results were validated with field data. Orientation data sets from the structural characterization were analyzed separately to assess best-fit probability density functions (PDF) for both dip angle and dip direction angle of each discontinuity set. A GIS-based stochastic kinematic analysis was then carried out using the discontinuity set orientations and the friction angle as random variables. An airborne laser scanning digital elevation model (ALS-DEM) with 1 m resolution was used for the analysis. Three failure mechanisms were analyzed: planar and wedge sliding, as well as toppling. Based on this kinematic analysis, areas where failure is feasible were used as source areas for run out analysis using Rockyfor3D v. 4.1 (www.ecorisq.org). The software calculates trajectories of single falling blocks in three dimensions using physically based algorithms developed under a stochastic approach. The ALS-DEM was down-scaled to 5 m resolution to optimize processing time. Results were compared with run-out simulations using Rockyfor3D with the whole rock wall as source area, and with maps of deposits generated from field observations and aerial photo interpretation. The results product of our implementation show a better correlation with field observations, and help to produce more accurate rock fall hazard assessment maps by a better definition of the source areas. It reduces the time processing for the analysis as well. The findings presented in this contribution are part of an effort to produce guidelines for natural hazard mapping in Norway. Guidelines will be used in upcoming years for hazard mapping in areas where larger groups of population are exposed to mass movements from steep slopes.

Self-Ordering and Complexity in Epizonal Mineral Deposits

NASA Astrophysics Data System (ADS)

Henley, Richard W.; Berger, Byron R.

Epizonal base and precious metal deposits makeup a range of familiar deposit styles including porphyry copper-gold, epithermal veins and stockworks, carbonate-replacement deposits, and polymetallic volcanic rock-hosted (VHMS) deposits. They occur along convergent plate margins and are invariably associated directly with active faults and volcanism. They are complex in form, variable in their characteristics at all scales, and highly localized in the earth's crust. More than a century of detailed research has provided an extensive base of observational data characterizing these deposits, from their regional setting to the fluid and isotope chemistry of mineral deposition. This has led to a broad understanding of the large-scale hydrothermal systems within which they form. Low salinity vapor, released by magma crystallization and dispersed into vigorously convecting groundwater systems, is recognized as a principal source of metals and the gases that control redox conditions within systems. The temperature and pressure of the ambient fluid anywhere within these systems is close to its vapor-liquid phase boundary, and mineral deposition is a consequence of short timescale perturbations generated by localized release of crustal stress. However, a review of occurrence data raises questions about ore formation that are not addressed by traditional genetic models. For example, what are the origins of banding in epithermal veins, and what controls the frequency of oscillatory lamination? What controls where the phenomenon of mineralization occurs, and why are some porphyry deposits, for example, so much larger than others? The distinctive, self-organized characteristics of epizonal deposits are shown to be the result of repetitive coupling of fracture dilation consequent on brittle failure, phase separation ("boiling"), and heat transfer between fluid and host rock. Process coupling substantially increases solute concentrations and triggers fast, far-from-equilibrium depositional processes. Since these coupled processes lead to localized transient changes in fluid characteristics, paragenetic, isotope, and fluid inclusion data relate to conditions at the site of deposition and only indirectly to the characteristics of the larger-scale hydrothermal system and its longer-term behavior. The metal concentrations (i.e. grade) of deposits and their internal variation is directly related to the geometry of the fracture array at the deposit scale, whereas finer-scale oscillatory fabrics in ores may be a result of molecular scale processes. Giant deposits are relatively rare and develop where efficient metal deposition is spatially focused by repetitive brittle failure in active fault arrays. Some brief case histories are provided for epithermal, replacement, and porphyry mineralization. These highlight how rock competency contrasts and feedback between processes, rather than any single component of a hydrothermal system, govern the size of individual deposits. In turn, the recognition of the probabilistic nature of mineralization provides a firmer foundation through which exploration investment and risk management decisions can be made.

Effects of Gas Pressure on the Failure Characteristics of Coal

NASA Astrophysics Data System (ADS)

Xie, Guangxiang; Yin, Zhiqiang; Wang, Lei; Hu, Zuxiang; Zhu, Chuanqi

2017-07-01

Several experiments were conducted using self-developed equipment for visual gas-solid coupling mechanics. The raw coal specimens were stored in a container filled with gas (99% CH4) under different initial gas pressure conditions (0.0, 0.5, 1.0, and 1.5 MPa) for 24 h prior to testing. Then, the specimens were tested in a rock-testing machine, and the mechanical properties, surface deformation and failure modes were recorded using strain gauges, an acoustic emission (AE) system and a camera. An analysis of the fractals of fragments and dissipated energy was performed to understand the changes observed in the stress-strain and crack propagation behaviour of the gas-containing coal specimens. The results demonstrate that increased gas pressure leads to a reduction in the uniaxial compression strength (UCS) of gas-containing coal and the critical dilatancy stress. The AE, surface deformation and fractal analysis results show that the failure mode changes during the gas state. Interestingly, a higher initial gas pressure will cause the damaged cracks and failure of the gas-containing coal samples to become severe. The dissipated energy characteristic in the failure process of a gas-containing coal sample is analysed using a combination of fractal theory and energy principles. Using the theory of fracture mechanics, based on theoretical analyses and calculations, the stress intensity factor of crack tips increases as the gas pressure increases, which is the main cause of the reduction in the UCS and critical dilatancy stress and explains the influence of gas in coal failure. More serious failure is created in gas-containing coal under a high gas pressure and low exterior load.

Estimation of Confined Peak Strength of Crack-Damaged Rocks

NASA Astrophysics Data System (ADS)

Bahrani, Navid; Kaiser, Peter K.

2017-02-01

It is known that the unconfined compressive strength of rock decreases with increasing density of geological features such as micro-cracks, fractures, and veins both at the laboratory specimen and rock block scales. This article deals with the confined peak strength of laboratory-scale rock specimens containing grain-scale strength dominating features such as micro-cracks. A grain-based distinct element model, whereby the rock is simulated with grains that are allowed to deform and break, is used to investigate the influence of the density of cracks on the rock strength under unconfined and confined conditions. A grain-based specimen calibrated to the unconfined and confined strengths of intact and heat-treated Wombeyan marble is used to simulate rock specimens with varying crack densities. It is demonstrated how such cracks affect the peak strength, stress-strain curve and failure mode with increasing confinement. The results of numerical simulations in terms of unconfined and confined peak strengths are used to develop semi-empirical relations that relate the difference in strength between the intact and crack-damaged rocks to the confining pressure. It is shown how these relations can be used to estimate the confined peak strength of a rock with micro-cracks when the unconfined and confined strengths of the intact rock and the unconfined strength of the crack-damaged rock are known. This approach for estimating the confined strength of crack-damaged rock specimens, called strength degradation approach, is then verified by application to published laboratory triaxial test data.

Assessing rockfall susceptibility in steep and overhanging slopes using three-dimensional analysis of failure mechanisms

USGS Publications Warehouse

Matasci, Battista; Stock, Greg M.; Jaboyedoff, Michael; Carrea, Dario; Collins, Brian D.; Guérin, Antoine; Matasci, G.; Ravanel, L.

2018-01-01

Rockfalls strongly influence the evolution of steep rocky landscapes and represent a significant hazard in mountainous areas. Defining the most probable future rockfall source areas is of primary importance for both geomorphological investigations and hazard assessment. Thus, a need exists to understand which areas of a steep cliff are more likely to be affected by a rockfall. An important analytical gap exists between regional rockfall susceptibility studies and block-specific geomechanical calculations. Here we present methods for quantifying rockfall susceptibility at the cliff scale, which is suitable for sub-regional hazard assessment (hundreds to thousands of square meters). Our methods use three-dimensional point clouds acquired by terrestrial laser scanning to quantify the fracture patterns and compute failure mechanisms for planar, wedge, and toppling failures on vertical and overhanging rock walls. As a part of this work, we developed a rockfall susceptibility index for each type of failure mechanism according to the interaction between the discontinuities and the local cliff orientation. The susceptibility for slope parallel exfoliation-type failures, which are generally hard to identify, is partly captured by planar and toppling susceptibility indexes. We tested the methods for detecting the most susceptible rockfall source areas on two famously steep landscapes, Yosemite Valley (California, USA) and the Drus in the Mont-Blanc massif (France). Our rockfall susceptibility models show good correspondence with active rockfall sources. The methods offer new tools for investigating rockfall hazard and improving our understanding of rockfall processes.

Seismological evidence for monsoon induced micro to moderate earthquake sequence beneath the 2011 Talala, Saurashtra earthquake, Gujarat, India

NASA Astrophysics Data System (ADS)

Singh, A. P.; Mishra, O. P.

2015-10-01

In order to understand the processes involved in the genesis of monsoon induced micro to moderate earthquakes after heavy rainfall during the Indian summer monsoon period beneath the 2011 Talala, Saurashtra earthquake (Mw 5.1) source zone, we assimilated 3-D microstructures of the sub-surface rock materials using a data set recorded by the Seismic Network of Gujarat (SeisNetG), India. Crack attributes in terms of crack density (ε), the saturation rate (ξ) and porosity parameter (ψ) were determined from the estimated 3-D sub-surface velocities (Vp, Vs) and Poisson's ratio (σ) structures of the area at varying depths. We distinctly imaged high-ε, high-ξ and low-ψ anomalies at shallow depths, extending up to 9-15 km. We infer that the existence of sub-surface fractured rock matrix connected to the surface from the source zone may have contributed to the changes in differential strain deep down to the crust due to the infiltration of rainwater, which in turn induced micro to moderate earthquake sequence beneath Talala source zone. Infiltration of rainwater during the Indian summer monsoon might have hastened the failure of the rock by perturbing the crustal volume strain of the causative source rock matrix associated with the changes in the seismic moment release beneath the surface. Analyses of crack attributes suggest that the fractured volume of the rock matrix with high porosity and lowered seismic strength beneath the source zone might have considerable influence on the style of fault displacements due to seismo-hydraulic fluid flows. Localized zone of micro-cracks diagnosed within the causative rock matrix connected to the water table and their association with shallow crustal faults might have acted as a conduit for infiltrating the precipitation down to the shallow crustal layers following the fault suction mechanism of pore pressure diffusion, triggering the monsoon induced earthquake sequence beneath the source zone.

Physical properties of two core samples from Well 34-9RD2 at the Coso geothermal field, California

USGS Publications Warehouse

Morrow, C.A.; Lockner, D.A.

2006-01-01

The Coso geothermal field, located along the Eastern California Shear Zone, is composed of fractured granitic rocks above a shallow heat source. Temperatures exceed 640 ?F (~338 ?C) at a depth of less than 10000 feet (3 km). Permeability varies throughout the geothermal field due to the competing processes of alteration and mineral precipitation, acting to reduce the interconnectivity of faults and fractures, and the generation of new fractures through faulting and brecciation. Currently, several hot regions display very low permeability, not conducive to the efficient extraction of heat. Because high rates of seismicity in the field indicate that the area is highly stressed, enhanced permeability can be stimulated by increasing the fluid pressure at depth to induce faulting along the existing network of fractures. Such an Enhanced Geothermal System (EGS), planned for well 46A-19RD, would greatly facilitate the extraction of geothermal fluids from depth by increasing the extent and depth of the fracture network. In order to prepare for and interpret data from such a stimulation experiment, the physical properties and failure behavior of the target rocks must be fully understood. Various diorites and granodiorites are the predominant rock types in the target area of the well, which will be pressurized from 10000 feet measured depth (MD) (3048m MD) to the bottom of the well at 13,000 feet MD (3962 m MD). Because there are no core rocks currently available from well 46A-19RD, we report here on the results of compressive strength, frictional sliding behavior, and elastic measurements of a granodiorite and diorite from another well, 34-9RD2, at the Coso site. Rocks cored from well 34-9RD2 are the deepest samples to date available for testing, and are representative of rocks from the field in general.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cook, J.M.; Sheppard, M.C.; Houwen, O.H.

Previous work on shale mechanical properties has focused on the slow deformation rates appropriate to wellbore deformation. Deformation of shale under a drill bit occurs at a very high rate, and the failure properties of the rock under these conditions are crucial in determining bit performance and in extracting lithology and pore-pressure information from drilling parameters. Triaxial tests were performed on two nonswelling shales under a wide range of strain rates and confining and pore pressures. At low strain rates, when fluid is relatively free to move within the shale, shale deformation and failure are governed by effective stress ormore » pressure (i.e., total confining pressure minus pore pressure), as is the case for ordinary rock. If the pore pressure in the shale is high, increasing the strain rate beyond about 0.1%/sec causes large increases in the strength and ductility of the shale. Total pressure begins to influence the strength. At high stain rates, the influence of effective pressure decreases, except when it is very low (i.e., when pore pressure is very high); ductility then rises rapidly. This behavior is opposite that expected in ordinary rocks. This paper briefly discusses the reasons for these phenomena and their impact on wellbore and drilling problems.« less

Evolution of wear and friction along experimental faults

USGS Publications Warehouse

Boneh, Yeval; Chang, Jefferson C.; Lockner, David A.; Reches, Zeev

2014-01-01

We investigate the evolution of wear and friction along experimental faults composed of solid rock blocks. This evolution is analyzed through shear experiments along five rock types, and the experiments were conducted in a rotary apparatus at slip velocities of 0.002–0.97 m/s, slip distances from a few millimeters to tens of meters, and normal stress of 0.25–6.9 MPa. The wear and friction measurements and fault surface observations revealed three evolution phases: A) An initial stage (slip distances <50 mm) of wear by failure of isolated asperities associated with roughening of the fault surface; B) a running-in stage of slip distances of 1–3 m with intense wear-rate, failure of many asperities, and simultaneous reduction of the friction coefficient and wear-rate; and C) a steady-state stage that initiates when the fault surface is covered by a gouge layer, and during which both wear-rate and friction coefficient maintain quasi-constant, low levels. While these evolution stages are clearly recognizable for experimental faults made from bare rock blocks, our analysis suggests that natural faults “bypass” the first two stages and slip at gouge-controlled steady-state conditions.

1963 Vajont rock slide: a comparison between 3D DEM and 3D FEM

NASA Astrophysics Data System (ADS)

Crosta, Giovanni; Utili, Stefano; Castellanza, Riccardo; Agliardi, Federico; Bistacchi, Andrea; Weng Boon, Chia

2013-04-01

Data on the exact location of the failure surface of the landslide have been used as the starting point for the modelling of the landslide. 3 dimensional numerical analyses were run employing both the discrete element method (DEM) and a Finite Element Method (FEM) code. In this work the focus is on the prediction of the movement of the landlside during its initial phase of detachment from Mount Toc. The results obtained by the two methods are compared and conjectures on the observed discrepancies of the predictions between the two methods are formulated. In the DEM simulations the internal interaction of the sliding blocks and the expansion of the debris is obtained as a result of the kinematic interaction among the rock blocks resulting from the jointing of the rock mass involved in the slide. In the FEM analyses, the c-phi reduction technique was employed along the predefine failure surface until the onset of the landslide occurred. In particular, two major blocks of the landslide were identified and the stress, strain and displacement fields at the interface between the two blocks were analysed in detail.

Rock Testing Handbook (Test Standards 1993)

DTIC Science & Technology

1993-01-01

surface. ergy lost due to nonuniformity of mediums. progressive failure-formation and development of localized refusal-in grouting, when the rate of...the components of mixed grout, resulting in nonuniform across which it acts. (ISRM) proportions in the mass. shear plane-a plane along which failure of...responr, le techndcal commttee, which you may attend if you teel mt your comments have not received a lair heating you should make your views known to the

Breaking rocks made easy: subcritical processes and tectonic predesign

NASA Astrophysics Data System (ADS)

Voigtlaender, Anne; Krautblatter, Michael

2017-04-01

In geomorphic studies, to change in landforms, e.g. by rock slope failure, fluvial or glacial erosion, a threshold is commonly assumed, which is crossed either by an increase in external driving or a decrease of internal resisting forces, respectively. If the threshold is crossed, bedrock breaks and slope fails, rivers incise and glaciers plug and sew their bed. Here we put forward a focus on the decrease of the resisting forces, as an increase in the driving forces, to match the strength of bedrock, is not that likely. We suggest that the degradation of resisting forces of bedrock can be better explained by subcritical processes like creep, fatigue and stress corrosion interplaying with tectonic predesign. Both concepts, subcritical processes and tectonic predesign have been issued in the last century, but have not been widely accepted nor have their assumptions been explicitly stressed in recent case studies. Moreover both concepts profit especially on scale issues if merged. Subcritical crack growth, includes different mechanisms promoting fractures well below the ultimate strength. Single infinitesimal but irreversible damage and deformations are induced in the material over time. They interact with inherent microstructural flaws and low applied stresses, limiting local strength and macroscopic behavior of bedrock. This reissues the concept of tectonic predesigned, as proposed by A.E. Scheidegger, which not only encompasses structural features that determine the routing of drainage patterns and shear planes, e.g. joints, faults and foliations, but also the (neo)tectonic stress-field and the (in-situ) strain state of bedrocks and mountains. Combining subcritical processes and tectonic predesign we can better explain, why and where we see a dissected, eroded and geomorphic divers' landscape. In this conceptual framework actual magnitudes of the driving forces are accounted for and so is the nature of the bedrock material, to better understand the trajectories of the forms we study, and break rocks easily.

A 3D geological and geomechanical model of the 1963 Vajont landslide

NASA Astrophysics Data System (ADS)

Bistacchi, Andrea; Massironi, Matteo; Francese, Roberto; Giorgi, Massimo; Chistolini, Filippo; Battista Crosta, Giovanni; Castellanza, Riccardo; Frattini, Paolo; Agliardi, Federico; Frigerio, Gabriele

2014-05-01

The Vajont rockslide has been the object of several studies because of its catastrophic consequences and particular evolution. Several qualitative or quantitative models have been presented in the last 50 years, but a complete explanation of all relevant geological and mechanical processes remains elusive. In order to better understand the mechanics and dynamics of the 1963 event, we have reconstructed the first 3D geological model of the rockslide, which allowed us to accurately investigate the rockslide structure and kinematics. The input data for the model consisted in: pre- and post-rockslide geological maps, pre- and post-rockslide orthophotos, pre- and post-rockslide digital elevation models, structural data, boreholes, and geophysical data (2D and 3D seismics and resistivity). All these data have been integrated in a 3D geological model implemented in Gocad®, using the implicit surface modelling method. Results of the 3D geological model include the depth and geometry of the sliding surface, the volume of the two lobes of the rockslide accumulation, kinematics of the rockslide in terms of the vector field of finite displacement, and high quality meshes useful for mechanical and hydrogeological simulations. The latter can include information about the stratigraphy and internal structure of the rock masses and allow tracing the displacement of different material points in the rockslide from the pre-1963-failure to the post-rockslide state. As a general geological conclusion, we may say that the 3D model allowed us to recognize very effectively a sliding surface, whose non-planar geometry is affected by the interference pattern of two regional-scale fold systems. The rockslide is partitioned into two distinct and internally continuous rock masses with a distinct kinematics, which were characterised by a very limited internal deformation during the slide. The continuity of these two large blocks points to a very localized deformation, occurring along a thin, continuous and weak cataclastic horizon. The chosen modelling strategy, based on both traditional "explicit" and implicit techniques, was found to be very effective for reconstructing complex folded and faulted geological structures, and could be applied also to other geological environments. Finally 3D FEM analyses using the code MidasGTS have been performed adopting the 3D geological model. A c-phi reduction procedure was employed along the pre-defined failure surface until the onset of the landslide occurred. The initiation of the rock mass movements is properly described by considering the evolution of plastic shear strain in the failure surface. The stress, strain and displacement fields of the rock mass were analysed in detail and compared with the monitored data.

Detecting Slow Deformation Signals Preceding Dynamic Failure: A New Strategy For The Mitigation Of Natural Hazards (SAFER)

NASA Astrophysics Data System (ADS)

Vinciguerra, S.; Colombero, C.; Comina, C.; Umili, G.

2015-12-01

Rock slope monitoring is a major aim in territorial risk assessment and mitigation. The use of "site specific" microseismic monitoring systems can allow to detect pre-failure signals in unstable sectors within the rock mass and to predict the possible acceleration to the failure. To this aim multi-scale geophysical methods can provide a unique tool for an high-resolution imaging of the internal structure of the rock mass and constraints on the physical state of the medium. We present here a cross-hole seismic tomography survey coupled with laboratory ultrasonic velocity measurements and determination of physical properties on rock samples to characterize the damaged and potentially unstable granitic cliff of Madonna del Sasso (NW, Italy). Results allowed to achieve two main advances, in terms of obtaining: i) a lithological interpretation of the velocity field obtained at the site, ii) a systematic correlation of the measured velocities with physical properties (density and porosity) and macroscopic features of the granite (weathering and anisotropy) of the cliff. A microseismic monitoring system developed by the University of Turin/Compagnia San Paolo, consisting of a network of 4 triaxial geophones (4.5 Hz) connected to a 12-channel data logger, has been deployed on the unstable granitic cliff. More than 2000 events with different waveforms, duration and frequency content were recorded between November 2013 and July 2014. By inspecting the acquired events we identified the key parameters for a reliable distinction among the nature of each signal, i.e. the signal shape (in terms of amplitude, duration, kurtosis) and the frequency content (maximum frequency content and frequency distribution). Four main classes of recorded signals can be recognised: microseismic events, regional earthquakes, electrical noises and calibration signals, and unclassified events (probably grouping rockfalls, quarry blasts, other anthropic and natural sources of seismic noise).

Experimental acidification of Little Rock Lake (Wisconsin): fish research approach and early responses.

PubMed

Swenson, W A; McCormick, J H; Simonson, T D; Jensen, K M; Eaton, J G

1989-01-01

One goal of research at Little Rock Lake, Wisconsin, is to enhance understanding of lake acidification effects on warm- and cool-water fishery resources. The Little Rock Lake fish assemblage is characteristic of many acid sensitive waters in North America and is dominated by yellow perch (Percidae) and sunfishes (Centrarchidae). Analyses of reproduction, early survival and growth rates in the field were designed around the differing reproductive modes of these taxa. Complementary laboratory research on early life stages was conducted to assist in isolating direct effect mechanisms and to determine the reliability of laboratory results in predicting field response. Preliminary findings suggest that lake acidification to pH 5.6 has not influenced reproductive activity of the four most abundant fish species. However, the field results suggest that year-class failure of rock bass (Ambloplites rupestris) may be occurring due to reduced survival of early life stages. Reduced growth and food conversion efficiency of Age 0 largemouth bass (Micropterus salmoides) is also suggested. The laboratory bioassays indicate rock bass is the most acid-sensitive Little Rock Lake species tested. However, rock bass fry survival was not significantly affected until pH was reduced from 5.6 to 5.0.

On the seismic response of instable rock slopes based on ambient vibration recordings

NASA Astrophysics Data System (ADS)

Kleinbrod, Ulrike; Burjánek, Jan; Fäh, Donat

2017-09-01

Rock slope failures can lead to huge human and economic loss depending on their size and exact location. Reasonable hazard mitigation requires thorough understanding of the underlying slope driving mechanisms and its rock mass properties. Measurements of seismic ambient vibrations could improve the characterization and detection of rock instabilities since there is a link between seismic response and internal structure of the unstable rock mass. An unstable slope near the village Gondo has been investigated. The unstable part shows strongly amplified ground motion with respect to the stable part of the rock slope. The amplification values reach maximum factors of 70. The seismic response on the instable part is highly directional and polarized. Re-measurements have been taken 1 year later showing exactly the same results as the original measurements. Neither the amplified frequencies nor the amplification values have changed. Therefore, ambient vibration measurements are repeatable and stay the same, if the rock mass has not undergone any significant change in structure or volume, respectively. Additionally, four new points have been measured during the re-measuring campaign in order to better map the border of the instability.[Figure not available: see fulltext.

Shear heating and metamorphism in subduction zones, 2. The seismic-aseismic transition at c. 50 km depth.

NASA Astrophysics Data System (ADS)

Castro, A. E.; Spear, F. S.; Kohn, M. J.

2017-12-01

Recent work demonstrates that shear heating, which is required for explaining fore-arc heat flow, reconciles thermal models with pressure-temperature (P-T) conditions determined from exhumed metamorphic rocks, i.e. exhumed rocks are representative of normal subduction. However, the range of subduction conditions on Earth (age, angle and rate of subducting plate, character of overriding plate, coefficient of friction, etc.) implies a ≥250 °C range of corresponding temperatures at the depth of the seismic-aseismic transition (SAT), which is consistently observed at 40-60 km in subduction zones worldwide. Here we show that the predicted rheologies and mineral stabilities for 3 common rock types fail to explain the global consistency of the SAT depth, and we propose that mechanical removal of the weakest rocks is required. Using either realistic thermal models, or P-T conditions recorded by exhumed metamorphic rocks, a substantial subset of depths corresponding with any single petrologic or rheological process falls outside the relatively restricted 40-60 km depth of the SAT. For example, a thermal weakening mechanism (the brittle-ductile transition) implies a wide range of depths, regardless of proposed T (e.g. 20-30 km (300 °C), 25-60 km (400 °C), 35 to >85 km (500 °C), etc). Similarly, individual dehydration reactions span a larger range of depths than observed for the SAT; for example, chlorite-out (metapelites: 35 to >85 km; metabasalts: 40 to >85 km), brucite-out (35-75 km) and serpentine/talc-out (50 to >80 km). The failure of a single petrologic and rheological trigger for these characteristic rocks to produce a consistent SAT depth implies that these rocks do not control the SAT, and consequently must not be abundant at depths below the SAT. That is, these hydrated, weak, and buoyant rocks must be squeezed out of the subduction system, although subduction of discontinuous blobs or lenses to greater depth, e.g. to feed arc volcanoes, may occur. The SAT instead may represent progressive strengthening of the subduction interface through mechanical exclusion of weak rocks and formation of stiffer minerals with increasing temperature and depth. Ultimately, as the strengths of the slab and mantle wedge converge at c. 80 km depth, mechanical coupling occurs, driving mantle wedge convection.

Seismic performance of arch dams on non-homogeneous and discontinuous foundations (a case study: Karun 4 Dam)

NASA Astrophysics Data System (ADS)

Ferdousi, A.

2017-06-01

The present study set out to investigate the nonlinear seismic response of the dam-reservoir-rock foundation system, taking into consideration the effects of change in the material properties of discontinuous foundation. To this end, it is important to provide the proper modeling of truncated boundary conditions at the far-end of rock foundation and reservoir fluid domain and to correctly apply the in situ stresses for rock foundation. The nonlinear seismic response of an arch dam mainly depends on the opening and sliding of the dam body's contraction joints and foundation discontinuities, failure of the jointed rock and concrete materials, etc. In this paper, a time domain dynamic analysis of the 3D dam-reservoir-foundation interaction problem was performed by developing a nonlinear Finite Element program. The results of the analysis of Karun-4 Dam revealed the essential role of modeling discontinuities and boundary conditions of rock foundation under seismic excitation.

Effect of Anisotropy on the Long-Term Strength of Granite

NASA Astrophysics Data System (ADS)

Nara, Yoshitaka

2015-05-01

Granite rock mass is used for various rock engineering purposes. To ensure long-term stability, information about the subcritical crack growth (SCG) and an estimate of the long-term strength (LTS) of the rock are necessary. The influence of the anisotropy of granite on its LTS has not yet been clarified. In this study, the anisotropy of the long-term rock strength was investigated for two types of granite rocks, Oshima granite and Inada granite. Specifically, the effect of the anisotropy in crack propagation on the LTS was examined. The results showed that the LTS of granite is anisotropic, as are the fracture toughness and Brazilian tensile strength measured in this study. The LTS was lowest when crack propagation occurred parallel to the rift plane, where most of the microcracks occur. For Inada granite, which has an anisotropic SCG index, the degree of anisotropy of the LTS increased as the time-to-failure increased. This suggests that the LTS of granite is anisotropic.

An accelerating precursor to predict "time-to-failure" in creep and volcanic eruptions

NASA Astrophysics Data System (ADS)

Hao, Shengwang; Yang, Hang; Elsworth, Derek

2017-09-01

Real-time prediction by monitoring of the evolution of response variables is a central goal in predicting rock failure. A linear relation Ω˙Ω¨-1 = C(tf - t) has been developed to describe the time to failure, where Ω represents a response quantity, C is a constant and tf represents the failure time. Observations from laboratory creep failure experiments and precursors to volcanic eruptions are used to test the validity of the approach. Both cumulative and simple moving window techniques are developed to perform predictions and to illustrate the effects of data selection on the results. Laboratory creep failure experiments on granites show that the linear relation works well during the final approach to failure. For blind prediction, the simple moving window technique is preferred because it always uses the most recent data and excludes effects of early data deviating significantly from the predicted trend. When the predicted results show only small fluctuations, failure is imminent.

Investigation of the Quasi-Brittle Failure of Alashan Granite Viewed from Laboratory Experiments and Grain-Based Discrete Element Modeling

PubMed Central

Zhang, Luqing; Yang, Duoxing; Braun, Anika; Han, Zhenhua

2017-01-01

Granite is a typical crystalline material, often used as a building material, but also a candidate host rock for the repository of high-level radioactive waste. The petrographic texture—including mineral constituents, grain shape, size, and distribution—controls the fracture initiation, propagation, and coalescence within granitic rocks. In this paper, experimental laboratory tests and numerical simulations of a grain-based approach in two-dimensional Particle Flow Code (PFC2D) were conducted on the mechanical strength and failure behavior of Alashan granite, in which the grain-like structure of granitic rock was considered. The microparameters for simulating Alashan granite were calibrated based on real laboratory strength values and strain-stress curves. The unconfined uniaxial compressive test and Brazilian indirect tensile test were performed using a grain-based approach to examine and discuss the influence of mineral grain size and distribution on the strength and patterns of microcracks in granitic rocks. The results show it is possible to reproduce the uniaxial compressive strength (UCS) and uniaxial tensile strength (UTS) of Alashan granite using the grain-based approach in PFC2D, and the average mineral size has a positive relationship with the UCS and UTS. During the modeling, most of the generated microcracks were tensile cracks. Moreover, the ratio of the different types of generated microcracks is related to the average grain size. When the average grain size in numerical models is increased, the ratio of the number of intragrain tensile cracks to the number of intergrain tensile cracks increases, and the UCS of rock samples also increases with this ratio. However, the variation in grain size distribution does not have a significant influence on the likelihood of generated microcracks. PMID:28773201

Investigation of the Quasi-Brittle Failure of Alashan Granite Viewed from Laboratory Experiments and Grain-Based Discrete Element Modeling.

PubMed

Zhou, Jian; Zhang, Luqing; Yang, Duoxing; Braun, Anika; Han, Zhenhua

2017-07-21

Granite is a typical crystalline material, often used as a building material, but also a candidate host rock for the repository of high-level radioactive waste. The petrographic texture-including mineral constituents, grain shape, size, and distribution-controls the fracture initiation, propagation, and coalescence within granitic rocks. In this paper, experimental laboratory tests and numerical simulations of a grain-based approach in two-dimensional Particle Flow Code (PFC2D) were conducted on the mechanical strength and failure behavior of Alashan granite, in which the grain-like structure of granitic rock was considered. The microparameters for simulating Alashan granite were calibrated based on real laboratory strength values and strain-stress curves. The unconfined uniaxial compressive test and Brazilian indirect tensile test were performed using a grain-based approach to examine and discuss the influence of mineral grain size and distribution on the strength and patterns of microcracks in granitic rocks. The results show it is possible to reproduce the uniaxial compressive strength (UCS) and uniaxial tensile strength (UTS) of Alashan granite using the grain-based approach in PFC2D, and the average mineral size has a positive relationship with the UCS and UTS. During the modeling, most of the generated microcracks were tensile cracks. Moreover, the ratio of the different types of generated microcracks is related to the average grain size. When the average grain size in numerical models is increased, the ratio of the number of intragrain tensile cracks to the number of intergrain tensile cracks increases, and the UCS of rock samples also increases with this ratio. However, the variation in grain size distribution does not have a significant influence on the likelihood of generated microcracks.

Climate change impacts on mass movements--case studies from the European Alps.

PubMed

Stoffel, M; Tiranti, D; Huggel, C

2014-09-15

This paper addresses the current knowledge on climate change impacts on mass movement activity in mountain environments by illustrating characteristic cases of debris flows, rock slope failures and landslides from the French, Italian, and Swiss Alps. It is expected that events are likely to occur less frequently during summer, whereas the anticipated increase of rainfall in spring and fall could likely alter debris-flow activity during the shoulder seasons (March, April, November, and December). The magnitude of debris flows could become larger due to larger amounts of sediment delivered to the channels and as a result of the predicted increase in heavy precipitation events. At the same time, however, debris-flow volumes in high-mountain areas will depend chiefly on the stability and/or movement rates of permafrost bodies, and destabilized rock glaciers could lead to debris flows without historic precedents in the future. The frequency of rock slope failures is likely to increase, as excessively warm air temperatures, glacier shrinkage, as well as permafrost warming and thawing will affect and reduce rock slope stability in the direction that adversely affects rock slope stability. Changes in landslide activity in the French and Western Italian Alps will likely depend on differences in elevation. Above 1500 m asl, the projected decrease in snow season duration in future winters and springs will likely affect the frequency, number and seasonality of landslide reactivations. In Piemonte, for instance, 21st century landslides have been demonstrated to occur more frequently in early spring and to be triggered by moderate rainfalls, but also to occur in smaller numbers. On the contrary, and in line with recent observations, events in autumn, characterized by a large spatial density of landslide occurrences might become more scarce in the Piemonte region. Copyright © 2014 Elsevier B.V. All rights reserved.

Constitutive Modeling of the Thermomechanical Behavior of Rock Salt

NASA Astrophysics Data System (ADS)

Hampel, A.

2016-12-01

For the safe disposal of heat-generating high-level radioactive waste in rock salt formations, highly reliable numerical simulations of the thermomechanical and hydraulic behavior of the host rock have to be performed. Today, the huge progress in computer technology has enabled experts to calculate large and detailed computer models of underground repositories. However, the big ad­van­ces in computer technology are only beneficial when the applied material models and modeling procedures also meet very high demands. They result from the fact that the evaluation of the long-term integrity of the geological barrier requires an extra­polation of a highly nonlinear deforma­tion behavior to up to 1 million years, while the underlying experimental investigations in the laboratory or in situ have a duration of only days, weeks or at most some years. Several advanced constitutive models were developed and continuously improved to describe the dependences of various deformation phenomena in rock salt on in-situ relevant boundary conditions: transient and steady-state creep, evolution of damage and dilatancy in the DRZ, failure, post-failure behavior, residual strength, damage and dilatancy reduction, and healing. In a joint project series between 2004 and 2016, fundamental features of the advanced models were investigated and compared in detail with benchmark calculations. The study included procedures for the determination of characteristic salt-type-specific model parameter values and for the performance of numerical calculations of underground structures. Based on the results of this work and on specific laboratory investigations, the rock mechanical modeling is currently developed further in a common research project of experts from Germany and the United States. In this presentation, an overview about the work and results of the project series is given and the current joint research project WEIMOS is introduced.

Behavioural and neural modulation of win-stay but not lose-shift strategies as a function of outcome value in Rock, Paper, Scissors.

PubMed

Forder, Lewis; Dyson, Benjamin James

2016-09-23

Competitive environments in which individuals compete for mutually-exclusive outcomes require rational decision making in order to maximize gains but often result in poor quality heuristics. Reasons for the greater reliance on lose-shift relative to win-stay behaviour shown in previous studies were explored using the game of Rock, Paper, Scissors and by manipulating the value of winning and losing. Decision-making following a loss was characterized as relatively fast and relatively inflexible both in terms of the failure to modulate the magnitude of lose-shift strategy and the lack of significant neural modulation. In contrast, decision-making following a win was characterized as relatively slow and relatively flexible both in terms of a behavioural increase in the magnitude of win-stay strategy and a neural modulation of feedback-related negativity (FRN) and stimulus-preceding negativity (SPN) following outcome value modulation. The win-stay/lose-shift heuristic appears not to be a unified mechanism, with the former relying on System 2 processes and the latter relying on System 1 processes. Our ability to play rationally appears more likely when the outcome is positive and when the value of wins are low, highlighting how vulnerable we can be when trying to succeed during competition.

Numerical Borehole Breakdown Investigations using XFEM

NASA Astrophysics Data System (ADS)

Beckhuis, Sven; Leonhart, Dirk; Meschke, Günther

2016-04-01

During pressurization of a wellbore a typical downhole pressure record shows the following regimes: first the applied wellbore pressure balances the reservoir pressure, then after the compressive circumferential hole stresses are overcome, tensile stresses are induced on the inside surface of the hole. When the magnitude of these stresses reach the tensile failure stress of the surrounding rock medium, a fracture is initiated and propagates into the reservoir. [1] In standard theories this pressure, the so called breakdown pressure, is the peak pressure in the down-hole pressure record. However experimental investigations [2] show that the breakdown did not occur even if a fracture was initiated at the borehole wall. Drilling muds had the tendency to seal and stabilize fractures and prevent fracture propagation. Also fracture mechanics analysis of breakdown process in mini-frac or leak off tests [3] show that the breakdown pressure could be either equal or larger than the fracture initiation pressure. In order to gain a deeper understanding of the breakdown process in reservoir rock, numerical investigations using the extended finite element method (XFEM) for hydraulic fracturing of porous materials [4] are discussed. The reservoir rock is assumed to be pre-fractured. During pressurization of the borehole, the injection pressure, the pressure distribution and the position of the highest flux along the fracture for different fracturing fluid viscosities are recorded and the influence of the aforementioned values on the stability of fracture propagation is discussed. [1] YEW, C. H. (1997), "Mechanics of Hydraulic Fracturing", Gulf Publishing Company [2] MORITA, N.; BLACK, A. D.; FUH, G.-F. (1996), "Borehole Breakdown Pressure with Drilling Fluids". International Journal of Rock Mechanics and Mining Sciences 33, pp. 39-51 [3] DETOURNAY, E.; CARBONELL, R. (1996), "Fracture Mechanics Analysis of the Breakdown Process in Minifrac or Leakoff Test", Society of Petroleum Engineers, Inc. [4] MESCHKE, G.; Leonhart, D. (2015), "A generalized finite element method for hydro-mechanically coupled analysis of hydraulic fracturing problems using space-time variant enrichment functions." Computer Methods in Applied Mechanics and Engineering, 290:438 - 465

On the Dynamics of Rocking Motion of the Hard-Disk Drive Spindle Motor System

NASA Astrophysics Data System (ADS)

Wang, Joseph

Excessive rocking motion of the spindle motor system can cause track misregistration resulting in poor throughput or even drive failure. The chance of excessive disk stack rocking increases as a result of decreasing torsional stiffness of spindle motor bearing system due to the market demand for low profile hard drives. As the track density increases and the vibration specification becomes increasingly stringent, rocking motion of a spindle motor system deserves even more attention and has become a primary challenge for a spindle motor system designer. Lack of understanding of the rocking phenomenon combined with misleading paradox has presented a great difficulty in the effort of avoiding the rocking motion in the hard-disk drive industry. This paper aims to provide fundamental understanding of the rocking phenomenon of a rotating spindle motor system, to clarify the paradox in disk-drive industry and to provide a design guide to an optimized spindle system. This paper, theoretically and experimentally, covers a few important areas of industrial interest including the prediction of rocking natural frequencies and mode shape of a rotating spindle, free vibration, and frequency response under common forcing functions such as rotating and fixed-plane forcing functions. The theory presented here meets with agreeable experimental observation.

Modelling Geomechanical Heterogeneity of Rock Masses Using Direct and Indirect Geostatistical Conditional Simulation Methods

NASA Astrophysics Data System (ADS)

Eivazy, Hesameddin; Esmaieli, Kamran; Jean, Raynald

2017-12-01

An accurate characterization and modelling of rock mass geomechanical heterogeneity can lead to more efficient mine planning and design. Using deterministic approaches and random field methods for modelling rock mass heterogeneity is known to be limited in simulating the spatial variation and spatial pattern of the geomechanical properties. Although the applications of geostatistical techniques have demonstrated improvements in modelling the heterogeneity of geomechanical properties, geostatistical estimation methods such as Kriging result in estimates of geomechanical variables that are not fully representative of field observations. This paper reports on the development of 3D models for spatial variability of rock mass geomechanical properties using geostatistical conditional simulation method based on sequential Gaussian simulation. A methodology to simulate the heterogeneity of rock mass quality based on the rock mass rating is proposed and applied to a large open-pit mine in Canada. Using geomechanical core logging data collected from the mine site, a direct and an indirect approach were used to model the spatial variability of rock mass quality. The results of the two modelling approaches were validated against collected field data. The study aims to quantify the risks of pit slope failure and provides a measure of uncertainties in spatial variability of rock mass properties in different areas of the pit.

Experimental research on the electromagnetic radiation (EMR) characteristics of cracked rock.

PubMed

Song, Xiaoyan; Li, Xuelong; Li, Zhonghui; Cheng, Fuqi; Zhang, Zhibo; Niu, Yue

2018-03-01

Coal rock would emit the electromagnetic radiation (EMR) while deformation and fracture, and there exists structural body in the coal rock because of mining and geological structure. In this paper, we conducted an experimental test the EMR characteristics of cracked rock under loading. Results show that crack appears firstly in the prefabricated crack tip then grows stably parallel to the maximum principal stress, and the coal rock buckling failure is caused by the wing crack tension. Besides, the compressive strength significantly decreases because of the precrack, and the compressive strength increases with the crack angle. Intact rock EMR increases with the loading, and the cracked rock EMR shows stage and fluctuant characteristics. The bigger the angle, the more obvious the stage and fluctuant characteristics, that is EMR becomes richer. While the cracked angle is little, EMR is mainly caused by the electric charge rapid separates because of friction sliding. While the cracked angle is big, there is another significant contribution to EMR, which is caused by the electric dipole transient of crack expansion. Through this, we can know more clear about the crack extends route and the corresponding influence on the EMR characteristic and mechanism, which has important theoretical and practical significance to monitor the coal rock dynamical disasters.

Comprehensive Understanding of the Zipingpu Reservoir to the Ms8.0 Wenchuan Earthquake

NASA Astrophysics Data System (ADS)

Cheng, H.; Pang, Y. J.; Zhang, H.; Shi, Y.

2014-12-01

After the Wenchuan earthquake occurred, whether the big earthquake triggered by the storage of the Zipingpu Reservoir has attracted wide attention in international academic community. In addition to the qualitative discussion, many scholars also adopted the quantitative analysis methods to calculate the stress changes, but due to the different results, they draw very different conclusions. Here, we take the dispute of different teams in the quantitative calculation of Zipingpu reservoir as a starting point. In order to find out the key influence factors of quantitative calculation and know about the existing uncertainty elements during the numerical simulation, we analyze factors which may cause the differences. The preliminary results show that the calculation methods (analytical method or numerical method), dimension of models (2-D or 3-D), diffusion model, diffusion coefficient and focal mechanism are the main factors resulted in the differences, especially the diffusion coefficient of the fractured rock mass. The change of coulomb failure stress of the epicenter of Wenchuan earthquake attained from 2-D model is about 3 times of that of 3-D model. And it is not reasonable that only considering the fault permeability (assuming the permeability of rock mass as infinity) or only considering homogeneous isotropic rock mass permeability (ignoring the fault permeability). The different focal mechanisms also could dramatically affect the change of coulomb failure stress of the epicenter of Wenchuan earthquake, and the differences can research 2-7 times. And the differences the change of coulomb failure stress can reach several hundreds times, when selecting different diffusion coefficients. According to existing research that the magnitude of coulomb failure stress change is about several kPa, we could not rule out the possibility that the Zipingpu Reservoir may trigger the 2008 Wenchuan earthquake. However, for the background stress is not clear and coulomb failure stress change is too little, we also not sure there must be a connection between reservoir and earthquake. In future work, we should target on the basis of field survey and indoor experiment, improve the model and develop high performance simulation.

The Effect of Hydrous Supercritical Carbon Dioxide on the Mohr Coulomb Failure Envelope in Boise Sandstone

NASA Astrophysics Data System (ADS)

Choens, R. C., II; Dewers, T. A.; Ilgen, A.; Espinoza, N.; Aman, M.

2016-12-01

Experimental rock deformation was used to quantify the relationship between supercritical carbon dioxide (scCO2), water vapor, and failure strength in an analog for Tertiary sandstone saline formation reservoirs. Storing large volumes of carbon dioxide in depleted petroleum reservoirs and deep saline aquifers over geologic time is an important tool in mitigating effects of climate change. Carbon dioxide is injected as a supercritical phase, where it forms a buoyant plume. At brine-plume interfaces, scCO2 dissolves over time into the brine, lowering pH and perturbing the local chemical environment. Previous work has shown that the resulting geochemical changes at mineral-fluid interfaces can alter rock mechanical properties, generally causing a decrease in strength. Additionally, water from the native brine can dissolve into the scCO2 plume where it is present as humidity. This study investigates the effect of hydrous scCO2 and CO2-saturated brine on shear failure of Boise sandstone. Samples are held in a hydrostatic pressure vessel at 2250 PSI confining pressure (PC) and 70 C, and scCO2 at specific humidity is circulated through the core for 24 hours at 2000 PSI and 70 C. Experiments are conducted at relative humidity levels of 0, 14, 28, 42, 56, 70, 84, 98, and 100% relative humidity. After the scCO2 core flood is finished, triaxial compression experiments are conducted on the samples at room temperature and an axial strain rate of 10-5 sec-1. Experiments are conducted at 500, 1000, and 1500 PSI PC. The results demonstrate that water present as humidity in scCO2 can reduce failure strength and lower slopes of the Mohr-Coulomb failure envelope. These effects increase with increasing humidity, as dry scCO2 does not affect rock strength, and may be influenced by capillary condensation of water films from humid scCO2. The reductions in failure strength seen in this study could be important in predicting reservoir response to injection, reservoir caprock integrity, and borehole stability of injection wells. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Security Administration under contract DE-AC04-94AL85000. SAND2016-7552A

Mid-Holocene cluster of large-scale landslides revealed in the Southwestern Alps by 36Cl dating. Insight on an Alpine-scale landslide activity

NASA Astrophysics Data System (ADS)

Zerathe, Swann; Lebourg, Thomas; Braucher, Régis; Bourlès, Didier

2014-04-01

Although it is generally assumed that the internal structure of a slope (e.g. lithology and rock mass properties, inherited faults and heterogeneities, etc.) is preponderant for the progressive development of large-scale landslides, the ability to identify triggering factors responsible for final slope failures such as glacial debuttressing, seismic activities or climatic changes, especially when considering landslide cluster at an orogen-scale, is still debated. Highlighting in this study the spatial and temporal concordant clustering of deep-seated slope failures in the external Southwestern Alps, we discuss and review the possible causes for such wide-spread slope instabilities at both local and larger (Alpine) scale. High resolution field mapping coupled with electrical resistivity tomography first allows establishing an inventory of large landslides in the Southwestern Alps, determining their structural model, precising their depth limit (100-200 m) as well as the involved rock volumes (>107 m3). We show that they developed in the same geostructural context of thick mudstone layers overlain by faulted limestone and followed a block-spread model of deformation that could evolve in rock-collapse events. Cosmic ray exposure dating (CRE), using both 36Cl and 10Be in coexisting limestone and chert, respectively, has been carried out from the main scarps of six Deep Seated Landslides (DSL) and leads to landslide-failure CRE ages ranging from 3.7 to 4.7 ka. They highlighted: (i) mainly single and fast ruptures and (ii) a possible concomitant initiation with a main peak of activity between 3.3 and 5.1 ka, centered at ca 4.2 ka. Because this region was not affected by historical glaciations events, landslide triggering by glacial unloading can be excluded. The presented data combined with field observations preferentially suggest that these failures were climatically driven and were most likely controlled by high pressure changes in the karstic medium. In effect, the chronicle of failure-ages is concomitant to a well-known climatic pulse, the “4.2 ka” climate event characterized by intense hydrological perturbations associated to the heaviest rainfall period of the entire Holocene. Despite requiring further investigations and discussions, the dating of numerous events across the entire Alps during the middle Holocene period suggests a potential synchronous triggering of several large-scale gravitational-failures induced by the mid-Holocene climatic transition.

An alternative hypothesis for sink development above salt cavities in the Detroit area

USGS Publications Warehouse

Stump, Daniel; Nieto, A.S.; Ege, J.R.

1982-01-01

Subsidence and sink formation resulting from brining operations in the Windsor-Detroit area include the 1954 sink at the Canadian Salt Company brine field near Windsor, Ontario, and the 1971 sinks at the BASF Wyandotte Corporation brine field at Grosse Ile, Mich. Earlier investigations into both occurrences concluded that the mechanism of sink development consisted of the gradual stoping of poorly supported brine-gallery roof rock to the near surface with subsequent surface collapse. A more recent study attempted to describe the mechanism of sink development in terms of the geometry of a cylindrical chimney formed by stoping of roof rock, the height of a cavity at depth, the depth of overlying rock, and the bulking ratio of the rubble formed during stoping. Persons with extensive experience in solution mining in the Windsor-Detroit area have expressed doubt that the stoping mechanism could fully explain the development of these sinks. Further, they have proposed that the relatively shallow (300-ft-deep) Sylvania Sandstone, in this case, may be responsible for the sinks by a secondary undermining mechanism to be examined in this paper. The mechanism involves downwarping of the beds overlying the salt cavity and development of a shallower cavity in the Sylvania Sandstone by downward migration of cohesionless sand grains from the Sylvania through openings in the disturbed rock to the lower cavity. This study indicates that under natural conditions the Sylvania will not migrate, even in the presence of large underground water flows because the sandstone possesses some cohesion throughout its depth. However, further investigation has formulated a mechanism that could allow the Sylvania Sandstone to loose its cohesion in response to high horizontal stresses. These stresses could be the result of deformation that accompanies general subsidence and (or) of past geologic processes. Included in this study were experimental and analytical investigations. As determined by uniaxial and triaxial testing, the Sylvania Sandstone in the Detroit area has been shown to have low compressive strength. In addition, it exhibits an explosive type failure whereby over 50 percent of the sample is reduced to loose granular sand. As a result of these characteristics, the Sylvania Sandstone can loose its cohesion when subjected to high horizontal stresses. Efforts at mechanically modeling the Sylvania were made to account for the measurements and observations. Linear arch theory was used for an elastic analysis. Linear arch theory predicts two modes of failure: (1) arch crushing, a compressive failure of the upper portion of the arch due to compressive stresses exceeding the compressive strength of the material, and (2) arch collapse, a sagging of the beds due to compressive strains which reduce the arch line to a length less than the original arch length. The arch crushing mode of failure would then yield the loose granular sand as observed in laboratory testing. Arch collapse would simply result in bed sagging without granulation of the sandstone. Arch collapse is favored by thin-bedded material while arch crushing is favored by thick-bedded material. Arch crushing seems to be a likely mode of failure for the Windsor-Detroit sinks. It is believed that after a crushing failure the sand-water slurry (specific gravity 1.2) which exceeds the density of the cavity brine will migrate downward through cracks and open joints eventually reaching the practically limitless open spaces of the rubble column and salt cavity. As the extent of the cavity within the Sylvania increases in depth and width because of sand migration, a critical span will be reached where the immediately overlying upper Sylvania and the overlying Detroit River Dolomite will fail. The collapse will allow a path for the approximately 100 ft of clay to collapse, resulting in a sink as the surface manifestation.

Finite element analysis of the failure mechanism of gentle slopes in weak disturbed clays

NASA Astrophysics Data System (ADS)

Lollino, Piernicola; Mezzina, Giuseppe; Cotecchia, Federica

2014-05-01

Italian south-eastern Apennines are affected by a large number of deep slow active landslide processes that interact with urban structures and infrastructures throughout the region, thus causing damages and economic losses. For most landslide processes in the region, the main predisposing factors for instability are represented by the piezometric regime and the extremely poor mechanical properties of the weak disturbed clays in the lower and central portions of the slopes that are overlaid in some cases by a stiffer cap layer, formed of rocky flysch, e.g. alternations of rock and soil strata. Based on phenomenological approaches, landslide processes are deemed to be triggered within the weaker clay layer and later on to develop upward to the stiffer cap, with the shear bands reaching also high depths. The paper presents the results of two-dimensional numerical analyses of the failure mechanisms developing in the unstable slopes of the region, carried out by means of the finite element method (Plaxis 2011) applied to slope conditions representative for the region. In particular, the effects of slope inclination, along with the thickness and the strength of the material forming the caprock at the top of the slope, on the depth of the sliding surface, the mobilised strengths, the evolution of the landslide process and the predisposing factors of landsliding have been explored by means of the finite element analysis of an ideal case study representative of the typical geomechanical context of the region. In particular, the increase of slope inclination is shown to raise the depth of the shear band as well as to extend landslide scarp upwards, in accordance with the field evidence. Moreover, the numerical results indicate how the increase of the caprock thickness tends to confine the development of the shear band to the underlying weaker clay layer, so that the depth of the shear band is also observed to reduce, and when the stiffer top stratum becomes involved in the retrogression of the failure process. The numerical results allow also for the investigation of the variation in seepage conditions that combine with the variations in litostratigraphy in determining the variations of the features of the failure mechanism.

Conduit Stability and Collapse in Explosive Volcanic Eruptions: Coupling Conduit Flow and Failure Models

NASA Astrophysics Data System (ADS)

Mullet, B.; Segall, P.

2017-12-01

Explosive volcanic eruptions can exhibit abrupt changes in physical behavior. In the most extreme cases, high rates of mass discharge are interspaced by dramatic drops in activity and periods of quiescence. Simple models predict exponential decay in magma chamber pressure, leading to a gradual tapering of eruptive flux. Abrupt changes in eruptive flux therefore indicate that relief of chamber pressure cannot be the only control of the evolution of such eruptions. We present a simplified physics-based model of conduit flow during an explosive volcanic eruption that attempts to predict stress-induced conduit collapse linked to co-eruptive pressure loss. The model couples a simple two phase (gas-melt) 1-D conduit solution of the continuity and momentum equations with a Mohr-Coulomb failure condition for the conduit wall rock. First order models of volatile exsolution (i.e. phase mass transfer) and fragmentation are incorporated. The interphase interaction force changes dramatically between flow regimes, so smoothing of this force is critical for realistic results. Reductions in the interphase force lead to significant relative phase velocities, highlighting the deficiency of homogenous flow models. Lateral gas loss through conduit walls is incorporated using a membrane-diffusion model with depth dependent wall rock permeability. Rapid eruptive flux results in a decrease of chamber and conduit pressure, which leads to a critical deviatoric stress condition at the conduit wall. Analogous stress distributions have been analyzed for wellbores, where much work has been directed at determining conditions that lead to wellbore failure using Mohr-Coulomb failure theory. We extend this framework to cylindrical volcanic conduits, where large deviatoric stresses can develop co-eruptively leading to multiple distinct failure regimes depending on principal stress orientations. These failure regimes are categorized and possible implications for conduit flow are discussed, including cessation of eruption.

Weathering process in Sør Rondane Mountains, East Antarctica

NASA Astrophysics Data System (ADS)

Kanamaru, T.; Suganuma, Y.; Oiwane, H.; Miura, M.; Okuno, J.; Hayakawa, H.

2016-12-01

Weathering process under the hyper-arid and hypothermal environment is a key to understand the geomorphogic process and landscape evolution in Antarctica and on Mars. A nunber of studies have focused on weathering process of basaltic rocks in Antarctica, however, the nature of the weathering process of plutonic type rock, a common rock type on the Earth, have been less focused and remain unclear. Here, we report the physical/chemical weathering process of the granitic rocks obtained from Dronning Maud Land in East Antarctica based on a multiplicity of petrological approaches. Loss on Ignition (LOI) and major element composition of the crust and core of the rock samples indicate that chemical weathering process in this area seems to be very limited. The microscopic observations and laser-Raman micro spectroscopy for thin sections from the crust and core indicate that goethite grains are formed mainly in the vein around the crust, which is consistent with the higher Fe3+/Fe2+ contrast from the core to crust. A negative correlation between the rock hardness and color strength index (CSI) values also indicate that crust of rock samples tend to less hard than core due to cracking of the rock samples and following goethite formation. On the other hand, EPMA analysis indicates that original Fe-Ti oxide grains in the core of rock samples are damaged by weathering, and altered to hematite, and to non-stoichiometric Fe-Ti compound associated with ilmenite grans in case of the higher relative height samples. These reveal that the weathering process of the plutonic rocks under the hyper-cold and hypothermal environment are mainly controlled by oxidation, including iron hydroxide formation in the veins formed by mechanical distraction, and Fe-Ti oxide alteration in rock interior.

Crack-jump mechanism of microvein formation and its implications for stress cyclicity during extension fracturing

NASA Astrophysics Data System (ADS)

Caputo, Riccardo; Hancock, Paul L.

1998-11-01

It is well accepted and documented that faulting is produced by the cyclic behaviour of a stress field. Some extension fractures, such as veins characterised by the crack-seal mechanism, have also been presumed to result from repeated stress cycles. In the present note, some commonly observed field phenomena and relationships such as hackle marks and vein and joint spacing, are employed to argue that a stress field can also display cyclic behaviour during extensional fracturing. Indeed, the requirement of critical stress conditions for the occurrence of extensional failure events does not accord with the presence of contemporaneously open nearby parallel fractures. Therefore, because after each fracture event there is stress release within the surrounding volume of rock, high density sets of parallel extensional fractures also strongly support the idea that rocks undergo stress cyclicity during jointing and veining. A comparison with seismological data from earthquakes with dipole mechanical solutions, confirms that this process presently occurs at depth in the Earth crust. Furthermore, in order to explain dense sets of hair-like closely spaced microveins, a crack-jump mechanism is introduced here as an alternative to the crack-seal mechanism. We also propose that as a consequence of medium-scale stress cyclicity during brittle deformation, the re-fracturing of a rock mass occurs in either one or the other of these two possible ways depending on the ratio between the elastic parameters of the sealing material and those of the host rock. The crack-jump mechanism occurs when the former is stronger.

Full-field Measurements of Strain Localisation in Sandstone by Neutron Tomography and 3D-Volumetric Digital Image Correlation

NASA Astrophysics Data System (ADS)

Tudisco, E.; Hall, S. A.; Charalampidou, E. M.; Kardjilov, N.; Hilger, A.; Sone, H.

Recent studies have demonstrated that the combination of x-ray tomography during triaxial tests (;in-situ; tests) and 3D- volumetric Digital Image Correlation (3D-DIC) can provide important insight into the mechanical behaviour and deformation processes of granular materials such as sand. The application of these tools to investigate the mechanisms of failure in rocks is also of obvious interest. However, the relevant applied confining pressures for triaxial testing on rocks are higher than those on sands and therefore stronger pressure containment vessels, i.e., made of thick metal walls, are required. This makes in-situ x-ray imaging of rock deformation during triaxial tests a challenge. One possible solution to overcome this problem is to use neutrons, which should better penetrate the metal-walls of the pressure vessels. In this perspective, this work assesses the capability of neutron tomography with 3D-DIC to measure deformation fields in rock samples. Results from pre- and post-deformation neutron tomography of a Bentheim sandstone sample deformed ex-situ at 40 MPa show that clear images of the internal structure can be achieved and utilised for 3D-DIC analysis to reveal the details of the 3D strain field. From these results the character of the localised deformation in the study sample can thus be described. Furthermore, comparison with analyses based on equivalent x-ray tomography imaging of the same sample confirms the effectiveness of the method in relation to the more established x-ray based approach.

Slope failures in Northern Vermont, USA

USGS Publications Warehouse

Lee, F.T.; Odum, J.K.; Lee, J.D.

1997-01-01

Rockfalls and debris avalanches from steep hillslopes in northern Vermont are a continuing hazard for motorists, mountain climbers, and hikers. Huge blocks of massive schist and gneiss can reach the valley floor intact, whereas others may trigger debris avalanches on their downward travel. Block movement is facilitated by major joints both parallel and perpendicular to the glacially over-steepened valley walls. The slope failures occur most frequently in early spring, accompanying freeze/thaw cycles, and in the summer, following heavy rains. The study reported here began in August 1986 and ended in June 1989. Manual and automated measurements of temperature and displacement were made at two locations on opposing valley walls. Both cyclic-reversible and permanent displacements occurred during the 13-month monitoring period. The measurements indicate that freeze/thaw mechanisms produce small irreversible incremental movements, averaging 0.53 mm/yr, that displace massive blocks and produce rockfalls. The initial freeze/thaw weakening of the rock mass also makes slopes more susceptible to attrition by water, and heavy rains have triggered rockfalls and consequent debris flows and avalanches. Temperature changes on the rock surface produced time-dependent cyclic displacements of the rock blocks that were not instantaneous but lagged behind the temperature changes. Statistical analyses of the data were used to produce models of cyclic time-dependent rock block behavior. Predictions based solely on temperature changes gave poor results. A model using time and temperature and incorporating the lag effect predicts block displacement more accurately.

Spine growth mechanisms: friction and seismicity at Mt. Unzen, Japan

NASA Astrophysics Data System (ADS)

Hornby, Adrian; Kendrick, Jackie; Hirose, Takehiro; Henton De Angelis, Sarah; De Angelis, Silvio; Umakoshi, Kodo; Miwa, Takahiro; Wadsworth, Fabian; Dingwell, Don; Lavallee, Yan

2014-05-01

The final episode of dome growth during the 1991-1995 eruption of Mt. Unzen was characterised by spine extrusion accompanied by repetitive seismicity. This type of cyclic activity has been observed at several dome-building volcanoes and recent work suggests a source mechanism of brittle failure of magma in the conduit. Spine growth may proceed by densification and closure of permeable pathways within the uppermost conduit magma, leading to sealing of the dome and inflation of the edifice. Amplified stresses on the wall rock and plug cause brittle failure near the conduit wall once static friction forces are overcome, and during spine growth these fractures may propagate to the dome surface. The preservation of these features is rare, and the conduit is typically inaccessible; therefore spines, the extruded manifestation of upper conduit material, provide the opportunity to study direct evidence of brittle processes in the conduit. At Mt. Unzen the spine retains evidence for brittle deformation and slip, however mechanical constraints on the formation of these features and their potential impact on eruption dynamics have not been well constrained. Here, we conduct an investigation into the process of episodic spine growth using high velocity friction apparatus at variable shear slip rate (0.4-1.5 m.s-1) and normal stress (0.4-3.5 MPa) on dome rock from Mt. Unzen, generating frictional melt at velocity >0.4 m.s-1 and normal stress >0.7 MPa. Our results show that the presence of frictional melt causes a deviation from Byerlee's frictional rule for rock friction. Melt generation is a disequilibrium process: initial amphibole breakdown leads to melt formation, followed by chemical homogenization of the melt layer. Ultimately, the experimentally generated frictional melts have a similar final chemistry, thickness and comminuted clast size distribution, thereby facilitating the extrapolation of a single viscoelastic model to describe melt-lubricated slip events at Mt. Unzen. To that end we apply state of the art 2-phase rheological models to estimate the dynamic apparent viscosities acting on the slip plane during a given slip event. Physical parameters of individual slip events in the conduit are constrained through calculation of seismic moments from earthquake swarms recorded during spine growth at Unzen. The combination of experimental data and viscosity modelling for frictional melt with seismic analysis provides a model for material response during slip in the upper conduit at Unzen. This model may have applicability to other eruption modes and volcanoes and further our understanding of cyclic eruptive activity during lava dome formation.

Changes in crack shape and saturation during water penetration into stressed rock

NASA Astrophysics Data System (ADS)

Masuda, K.; Nishizawa, O.

2012-12-01

Open cracks and cavities in rocks play important roles in fluid transport. Water penetration induced microcrack activities and caused the failure of rocks. Fluids in cracks affect earthquake generation mechanism through physical and physicochemical effects. Methods of characterizing crack shape and water saturation of rocks underground are needed for many scientific and industrial applications. It would be desirable to estimate the status of cracks using readily observable data such as elastic-wave velocities. We demonstrate a laboratory method for estimating crack status inside a cylindrical rock sample based on least-squares fitting of a cracked solid model to measured P- and S-wave velocities, and porosity derived from strain data. We used a cylinder (50 mm in diameter and 100 mm in length) of medium-grained granite. We applied a differential stress of 370 MPa, which corresponds to about 70% of fracture strength, to the rock sample under 30 MPa confining pressure and held it constant throughout the experiment. When the primary creep stage and acoustic emission (AE) caused by the initial loading had ceased, we injected distilled water into the bottom end of the sample at a constant pressure of 25 MPa until macroscopic fracture occurred. During water migration, we measured P waves and S waves (Sv and Sh), in five directions parallel to the top and bottom surfaces of the sample. We also measured strains of the sample surface and monitored AE. We created X-ray computer tomography (CT) images of the rock sample after the experiment in order to recognize the location and shape of fractured surfaces. We observed the different patterns of velocity changes in the upper and lower portions of the rock sample. Changes in P-wave velocities can be interpreted based on the crack density. S-waves showed the splitting with Vsv being faster than Vsh, corresponding to the second kind of anisotropy. We estimated two crack characteristics, crack shape and the degree of water saturation, and their changes during the loading and water migration into a granitic rock subjected to confining pressure and differential stress. We found that during injection of water to induce failure of a stressed rock sample, the aspect ratio of cracks increased and the degree of water saturation increased to about 70%. Laboratory derived method can be applicable for the well-planned observation in the field experiments. Monitoring in situ crack situations with seismic waves are useful for industrial and scientific applications such as sequestrations of carbon dioxide and waste, and measuring the regional stress field.

Pore Effect on the Occurrence and Formation of Gas Hydrate in Permafrost of Qilian Mountain, Qinghai-Tibet Plateau, China

NASA Astrophysics Data System (ADS)

Gao, H.; Lu, H.; Lu, Z.

2014-12-01

Gas hydrates were found in the permafrost of Qilian Mountain, Qinghai- Tibet Plateau, China in 2008. It has been found that gas hydrates occur in Jurassic sedimentary rocks, and the hydrated gases are mainly thermogenic. Different from the gas hydrates existing in loose sands in Mallik, Mackenzie Delta, Canada and North Slope, Alaska, USA, the gas hydrates in Qilian Mountain occurred in hard rocks. For understanding the occurrence and formation mechanism of gas hydrate in hard rcok, extensive experimental investigations have been conducted to study the pore features and hydrate formation in the rocks recovered from the hydrate layers in Qilian Mountain. The structures of sedimentary rock were observed by high-resolution X-ray CT, and pore size distribution of a rock specimen was measured with the mercury-injection method. Methane hydrate was synthesized in water-saturated rocks, and the saturations of hydrate in sedimentary rocks of various types were estimated from the amount of gas released from certain volume of rock. X-ray CT observation revealed that fractures were developed in the rocks associated with faults, while those away from faults were generally with massive structure. The mercury-injection analysis of pore features found that the porosities of the hydrate-existing rocks were generally less than 3%, and the pore sizes were generally smaller than 100 nm. The synthesizing experiments found that the saturation of methane hydrate were generally lower than 6% of pore space in rocks, but up to 16% when fractures developed. The low hydrate saturation in Qilian sedimentary rocks has been found mainly due to the small pore size of rock. The low hydrate saturation in the rocks might be the reason for the failure of regional seismic and logging detections of gas hydrates in Qilian Mountain.

Analysis of the evolution of the instability process of a coastal cavern

NASA Astrophysics Data System (ADS)

Lollino, P.; Reina, A.

2012-04-01

This work concerns the study performed for the interpretation of the potential failure mechanism of a large natural cavern, which is located along the rocky cliffs of Polignano a Mare town (Apulia, Southern Italy) under an intensely urbanised area. This cavern, which is located at the sea level, was formed due to an intense process of salt and wave erosion, mainly acting during sea storms, within a rock mass formed of a lower stratified limestone mass and an upper soft calcarenite mass. Therefore, the influence of the climatic factors and of the upward erosion process within the cavern has been specifically investigated. At present, the thickness of the cave roof, which has a dome shape, is less than 10 metres in the centre and several buildings are founded on the ground surface above. In 2006 a large calcarenite block, of about 1.5 m diameter, fell down from the roof of the cavern and afterwards field and laboratory investigations as well as both simple analytical methods and elasto-plastic numerical modelling were carried out in order to assess the current state of the roof and to interpret the effects of the potential evolution of the inner erosion and of the local failure processes of the cave. As such, a detailed geo-structural survey has firstly been carried out, together with laboratory and in-situ testing for the geomechanical characterisation of the rock materials and of the corresponding joints. An analysis of the sea storms occurred within the observation period has also been performed by considering daily rainfall and wind data. The rate of erosion has been measured by means of special nets installed at the sea level to collect the material falling down from the roof and the corresponding measurements, which lasted for about one year, indicate an erosion rate of at least 0.005 m3/month. A structural monitoring system, including extensometers and joint-meters, was also installed in several points of the cave in order to measure eventual block displacements within the cavern and the results show some correlations of the logged data with the occurrence of sea storms and in general with the weather factors. The results of both simplified analytical methods and numerical analysis show that the cave is at present stable. Also, numerical modelling was aimed at defining the conditions under which general failure of the cave might occur. In particular, sensitivity analyses have been carried out to assess the influence of specific factors, as the progressive reduction of the roof thickness due to erosion or the gradual reduction of the strength properties of the calcarenite due to weathering processes.

Investigation of subsidence along segment of Missouri Route 65, Springfield, Missouri.

DOT National Transportation Integrated Search

2010-02-01

Electrical Resistivity Tomography (ERT) data were acquired on the ground surface across an underground limestone mine access tunnel in an effort to characterize the roof rock. This investigation was conducted because simultaneous localized failure oc...

Integrating GIS-based geologic mapping, LiDAR-based lineament analysis and site specific rock slope data to delineate a zone of existing and potential rock slope instability located along the grandfather mountain window-Linville Falls shear zone contact, Southern Appalachian Mountains, Watauga County, North Carolina

USGS Publications Warehouse

Gillon, K.A.; Wooten, R.M.; Latham, R.L.; Witt, A.W.; Douglas, T.J.; Bauer, J.B.; Fuemmeler, S.J.

2009-01-01

Landslide hazard maps of Watauga County identify >2200 landslides, model debris flow susceptibility, and evaluate a 14km x 0.5km zone of existing and potential rock slope instability (ZEPRSI) near the Town of Boone. The ZEPRSI encompasses west-northwest trending (WNWT) topographic ridges where 14 active/past-active rock/weathered rock slides occur mainly in rocks of the Grandfather Mountain Window (GMW). The north side of this ridgeline is the GMW / Linville Falls Fault (LFF) contact. Sheared rocks of the Linville Falls Shear Zone (LFSZ) occur along the ridge and locally in the valley north of the contact. The valley is underlain principally by layered granitic gneiss comprising the Linville Falls/Beech Mountain/Stone Mountain Thrust Sheet. The integration of ArcGIS??? - format digital geologic and lineament mapping on a 6m LiDAR (Light Detecting and Ranging) digital elevation model (DEM) base, and kinematic analyses of site specific rock slope data (e.g., presence and degree of ductile and brittle deformation fabrics, rock type, rock weathering state) indicate: WNWT lineaments are expressions of a regionally extensive zone of fractures and faults; and ZEPRSI rock slope failures concentrate along excavated, north-facing LFF/LFSZ slopes where brittle fabrics overprint older metamorphic foliations, and other fractures create side and back release surfaces. Copyright 2009 ARMA, American Rock Mechanics Association.

Coulombic faulting from the grain scale to the geophysical scale: lessons from ice

NASA Astrophysics Data System (ADS)

Weiss, Jérôme; Schulson, Erland M.

2009-11-01

Coulombic faulting, a concept formulated more than two centuries ago, still remains pertinent in describing the brittle compressive failure of various materials, including rocks and ice. Many questions remain, however, about the physical processes underlying this macroscopic phenomenology. This paper reviews the progress made in these directions during the past few years through the study of ice and its mechanical behaviour in both the laboratory and the field. Fault triggering is associated with the formation of specific features called comb-cracks and involves frictional sliding at the micro(grain)-scale. Similar mechanisms are observed at geophysical scales within the sea ice cover. This scale-independent physics is expressed by the same Coulombic phenomenology from laboratory to geophysical scales, with a very similar internal friction coefficient (μ ≈ 0.8). On the other hand, the cohesion strongly decreases with increasing spatial scale, reflecting the role of stress concentrators on fault initiation. Strong similarities also exist between ice and other brittle materials such as rocks and minerals and between faulting of the sea ice cover and Earth's crust, arguing for the ubiquitous nature of the underlying physics.

High resolution digital mapping and geomorphological analysis of the 2010 Mount Meager rock-debris avalanche (BC, Canada).

NASA Astrophysics Data System (ADS)

Roberti, Gioachino; van Wyk de vries, Benjamin; Ward, Brent; Clague, John; Friele, Pierre; Perotti, Luigi; Giardino, Marco

2016-04-01

This study examines the large landslide that occurred at Mt. Meager, 200 km NNW of Vancouver, British Columbia, Canada, on August 6, 2010. We studied the source area and deposits to reconstruct the failure of the south flank of Mt. Meager from slow deformation to catastrophic collapse, the subsequent transformation into a debris avalanche, and the 11 km run-out. We use a Structure from Motion (SfM) photogrammetric approach and processed both historical British Columbia Provincial airphotos (1948, 1962, 1964-1965, 1973, 1981, 1990, and 2006) and digital images taken with a commercial camera during low-level helicopter traverses. The SfM products have been used to calculate volumes and the geometry of the south flank of Mt. Meager before and after the catastrophic failure, and to produce an orthophoto that we have used to map and describe the deposit. Oblique helicopter photos provide information on the scar geometry and rock units exposed by the failure. The SfM-derived orthophoto and ground observations allowed us to map deposit facies, lithologies, and structures, including thrust, normal, and strike-slip faults. We identified five sub-areas in the accumulation zone based on the association of facies and deformation structures. Based on our interpretation of the remotely sensed data and ground observations, we propose that the landslide had two main rheological phases: one richer in water and highly mobile, and another massive and water-poor. The water-rich phase spread quickly and superelevated high on valley walls as it moved down valley. It left a discontinuous veneer of debris, typically <1 m thick. The main, unsaturated mass moved more slowly and left a thicker (up to about 20 m) deposit with hummocks and brittle-ductile faults and shear zone in the distal part of the run-out zone.

3D Coda Attenuation Tomography of Acoustic Emission Data from Laboratory Samples as a tool for imaging pre-failure deformation mechanisms

NASA Astrophysics Data System (ADS)

Vinciguerra, S.; King, T. I.; Benson, P. M.; De Siena, L.

2017-12-01

In recent years, 3D and 4D seismic tomography have unraveled medium changes during the seismic cycle or before eruptive events. As our resolving power increases, however, complex structures increasingly affect images. Being able to interpret and understand these features requires a multi-discipline approach combining different methods, each sensitive to particular properties of the sub-surface. Rock deformation laboratory experiments can relate seismic properties to the evolving medium quantitatively. Here, an array of 1 MHz Piezo-Electric Transducers has recorded high-quality low-noise acoustic emission (AE) data during triaxial compressional experiments. Samples of Carrara Marble, Darley Dale Sandstone and Westerly Granite were deformed in saturated conditions representative of a depth of about 1 km until brittle failure. Using a time window around sample failure, AE data were filtered between 5 and 75 KHz and processed using a 3D P-coda attenuation-tomography method. Ratios of P-direct to P-coda energies calculated for each source-receiver path were inverted using the coda normalisation method for values of Q (P-wave quality factor). The results show Q-variation with respect to an average Q. Q is a combination of the effects of scattering attenuation (Qs) and intrinsic attenuation Q (Qi), which can be correlated to the sample structure. Qs primary controls energy dissipation in the presence at acoustic impedance (AI) surfaces and at fracture tips, independently of rock type, while pore fluid effects dissipate energy (Qi). Damaged zones appear as high-Q and low-Q anomalies in unsaturated and saturated samples, respectively. We have attributed frequency-dependent high-Q to resonance in the presence of AI surfaces. Low Q areas appear behind AI surfaces and are interpreted as energy shadows. These shadows can affect attenuation tomography imaging at field scale.

Tightness of Salt Rocks and Fluid Percolation

NASA Astrophysics Data System (ADS)

Lüdeling, C.; Minkley, W.; Brückner, D.

2016-12-01

Salt formations are used for storage of oil and gas and as waste repositiories because of their excellent barrier properties. We summarise the current knowledge regarding fluid tightness of saliferous rocks, in particular rock salt. Laboratory results, in-situ observations and natural analogues, as well as theoretical and numerical investigations, indicate that pressure-driven percolation is the most important mechanism for fluid transport: If the fluid pressure exceeds the percolation threshold, i.e. the minor principal stress, the fluid can open up grain boundaries, create connected flow paths and initiate directed migration in the direction of major principal stress. Hence, this mechanism provides the main failure mode for rock salt barriers, where integrity can be lost if the minor principal stress is lowered, e.g. due to excavations or thermomechanical uplift. We present new laboratory experiments showing that there is no fluid permeation below the percolation threshold also at high temperatures and pressures, contrary to recent claims in the literature.

Energy Dissipation-Based Method for Fatigue Life Prediction of Rock Salt

NASA Astrophysics Data System (ADS)

He, Mingming; Huang, Bingqian; Zhu, Caihui; Chen, Yunsheng; Li, Ning

2018-05-01

The fatigue test for rock salt is conducted under different stress amplitudes, loading frequencies, confining pressures and loading rates, from which the evaluation rule of the dissipated energy is revealed and analysed. The evolution of energy dissipation under fatigue loading is divided into three stages: the initial stage, the second stage and the acceleration stage. In the second stage, the energy dissipation per cycle remains stable and shows an exponential relation with the stress amplitude; the failure dissipated energy only depends on the mechanical behaviour of the rock salt and confining pressure, but it is immune to the loading conditions. The energy dissipation of fatigued rock salt is discussed, and a novel model for fatigue life prediction is proposed on the basis of energy dissipation. A simple model for evolution of the accumulative dissipated energy is established. Its prediction results are compared with the test results, and the proposed model is validated.

Using volcanic tremor for eruption forecasting at White Island volcano (Whakaari), New Zealand

NASA Astrophysics Data System (ADS)

Chardot, Lauriane; Jolly, Arthur D.; Kennedy, Ben M.; Fournier, Nicolas; Sherburn, Steven

2015-09-01

Eruption forecasting is a challenging task because of the inherent complexity of volcanic systems. Despite remarkable efforts to develop complex models in order to explain volcanic processes prior to eruptions, the material Failure Forecast Method (FFM) is one of the very few techniques that can provide a forecast time for an eruption. However, the method requires testing and automation before being used as a real-time eruption forecasting tool at a volcano. We developed an automatic algorithm to issue forecasts from volcanic tremor increase episodes recorded by Real-time Seismic Amplitude Measurement (RSAM) at one station and optimised this algorithm for the period August 2011-January 2014 which comprises the recent unrest period at White Island volcano (Whakaari), New Zealand. A detailed residual analysis was paramount to select the most appropriate model explaining the RSAM time evolutions. In a hindsight simulation, four out of the five small eruptions reported during this period occurred within a failure window forecast by our optimised algorithm and the probability of an eruption on a day within a failure window was 0.21, which is 37 times higher than the probability of having an eruption on any day during the same period (0.0057). Moreover, the forecasts were issued prior to the eruptions by a few hours which is important from an emergency management point of view. Whereas the RSAM time evolutions preceding these four eruptions have a similar goodness-of-fit with the FFM, their spectral characteristics are different. The duration-amplitude distributions of the precursory tremor episodes support the hypothesis that several processes were likely occurring prior to these eruptions. We propose that slow rock failure and fluid flow processes are plausible candidates for the tremor source of these episodes. This hindsight exercise can be useful for future real-time implementation of the FFM at White Island. A similar methodology could also be tested at other volcanoes even if only a limited network is available.

Using Seismic Signals to Forecast Volcanic Processes

NASA Astrophysics Data System (ADS)

Salvage, R.; Neuberg, J. W.

2012-04-01

Understanding seismic signals generated during volcanic unrest have the ability to allow scientists to more accurately predict and understand active volcanoes since they are intrinsically linked to rock failure at depth (Voight, 1988). In particular, low frequency long period signals (LP events) have been related to the movement of fluid and the brittle failure of magma at depth due to high strain rates (Hammer and Neuberg, 2009). This fundamentally relates to surface processes. However, there is currently no physical quantitative model for determining the likelihood of an eruption following precursory seismic signals, or the timing or type of eruption that will ensue (Benson et al., 2010). Since the beginning of its current eruptive phase, accelerating LP swarms (< 10 events per hour) have been a common feature at Soufriere Hills volcano, Montserrat prior to surface expressions such as dome collapse or eruptions (Miller et al., 1998). The dynamical behaviour of such swarms can be related to accelerated magma ascent rates since the seismicity is thought to be a consequence of magma deformation as it rises to the surface. In particular, acceleration rates can be successfully used in collaboration with the inverse material failure law; a linear relationship against time (Voight, 1988); in the accurate prediction of volcanic eruption timings. Currently, this has only been investigated for retrospective events (Hammer and Neuberg, 2009). The identification of LP swarms on Montserrat and analysis of their dynamical characteristics allows a better understanding of the nature of the seismic signals themselves, as well as their relationship to surface processes such as magma extrusion rates. Acceleration and deceleration rates of seismic swarms provide insights into the plumbing system of the volcano at depth. The application of the material failure law to multiple LP swarms of data allows a critical evaluation of the accuracy of the method which further refines current understanding of the relationship between seismic signals and volcanic eruptions. It is hoped that such analysis will assist the development of real time forecasting models.

Hydrogeochemical and isotopic studies of groundwater in the middle voltaian aquifers of the Gushegu district of the Northern region

NASA Astrophysics Data System (ADS)

Salifu, Musah; Yidana, Sandow Mark; Anim-Gyampo, Maxwell; Appenteng, Michael; Saka, David; Aidoo, Felix; Gampson, Enoch; Sarfo, Mark

2017-06-01

This work is to establish the hydrochemistry and origin of groundwater in some parts of the Gushegu district of the Northern Region of Ghana. Hydrochemical data from 19 groundwater and 7 rock samples have been used to evaluate water quality, water types, and sources of various ions as well as origin of the groundwater. The study results show that the quality of groundwater from the area is generally not good due to their fluoride (F-), bicarbonate (HCO3 -) and electrical conductivity (EC) concentrations. The F- contents of the groundwater have values as high as 1.97 mg/L, with 53 % of the groundwater having concentrations of F- exceeding the WHO recommended allowable limits. These high F- values have the potential of causing serious health problems such as kidney failure, dental and skeletal fluorosis, reproductive problem and reduction in intelligent quotient of consumers. A plot of Gibbs diagram reveals that rock weathering and precipitation are the major hydrogeochemical processes regulating the water chemistry of the study area. Petrographic thin-section analyses of rock samples identify minerals present to be muscovite, plagioclase feldspars, quartz, sericite and iron oxide. Stable isotope (18O and 2H) composition of the waters reveals that most of the groundwater is likely to be recharged from local precipitation, indicating their meteoric origin. Some samples, however, showed considerable evaporation.

Brittle deformation and slope failure at the North Menan Butte tuff cone, Eastern Snake River Plain, Idaho

USGS Publications Warehouse

Okubo, Chris H.

2014-01-01

The manifestation of brittle deformation within inactive slumps along the North Menan Butte, a basaltic tuff cone in the Eastern Snake River Plain, is investigated through field and laboratory studies. Microstructural observations indicate that brittle strain is localized along deformation bands, a class of structural discontinuity that is predominant within moderate to high-porosity, clastic sedimentary rocks. Various subtypes of deformation bands are recognized in the study area based on the sense of strain they accommodate. These include dilation bands (no shear displacement), dilational shear bands, compactional shear bands and simple shear bands (no volume change). Measurements of the host rock permeability between the deformation bands indicate that the amount of brittle strain distributed throughout this part of the rock is negligible, and thus deformation bands are the primary means by which brittle strain is manifest within this tuff. Structural discontinuities that are similar in appearance to deformation bands are observed in other basaltic tuffs. Therefore deformation bands may represent a common structural feature of basaltic tuffs that have been widely misclassified as fractures. Slumping and collapse along the flanks of active volcanoes strongly influence their eruptive behavior and structural evolution. Therefore characterizing the process of deformation band and fault growth within basaltic tuff is key to achieving a more complete understanding of the evolution of basaltic volcanoes and their associated hazards.

Numerical analysis of the performance of rock weirs: Effects of structure configuration on local hydraulics

USGS Publications Warehouse

Holmquist-Johnson, C. L.

2009-01-01

River spanning rock structures are being constructed for water delivery as well as to enable fish passage at barriers and provide or improve the aquatic habitat for endangered fish species. Current design methods are based upon anecdotal information applicable to a narrow range of channel conditions. The complex flow patterns and performance of rock weirs is not well understood. Without accurate understanding of their hydraulics, designers cannot address the failure mechanisms of these structures. Flow characteristics such as jets, near bed velocities, recirculation, eddies, and plunging flow govern scour pool development. These detailed flow patterns can be replicated using a 3D numerical model. Numerical studies inexpensively simulate a large number of cases resulting in an increased range of applicability in order to develop design tools and predictive capability for analysis and design. The analysis and results of the numerical modeling, laboratory modeling, and field data provide a process-based method for understanding how structure geometry affects flow characteristics, scour development, fish passage, water delivery, and overall structure stability. Results of the numerical modeling allow designers to utilize results of the analysis to determine the appropriate geometry for generating desirable flow parameters. The end product of this research will develop tools and guidelines for more robust structure design or retrofits based upon predictable engineering and hydraulic performance criteria. ?? 2009 ASCE.

Carbon-enhanced electrical conductivity during fracture of rocks

NASA Astrophysics Data System (ADS)

Roberts, J. J.; Duba, A. G.; Mathez, E. A.; Shankland, T. J.; Kinzler, R.

1999-01-01

Changes in electrical resistance during rock fracture in the presence of a carbonaceous atmosphere have been investigated using Nugget sandstone and Westerly granite. The experiments were performed in an internally heated, gas-pressure vessel with a load train that produced strain rates between 10-6 and 10-5 s-1. Samples were deformed at temperatures of 354° to 502°C and pressures of 100 to 170 MPa in atmospheres of Ar or mixtures of 95% CO2 with 5% CO or 5% CH4, compositions that are well within the field of graphite stability at the run conditions. In experiments using Nugget sandstone, resistance reached a minimum value when the maximum temperature was achieved and good electrode contact was made. The resistance then increased as the experiment continued, probably due to dry out of the sample, a change in the oxidation state of the Fe-oxide associated with the cement, or destruction of current-bearing pathways. At approximately 200-MPa end load, the rock sample failed. Plots of load and resistance versus time show several interesting features. In one experiment, for example, as the end load reached about 175 MPa, resistance stopped increasing and remained fairly constant for a period of approximately 0.5 hour. During loading, the end load displayed small decreases that were simultaneous with small decreases in resistance; when the end load (and the displacement) indicated rock failure, resistance decreased dramatically, from ˜150 MΩ to 100 MΩ. In a single experiment, the Westerly granite also showed a decrease in resistance during dilatancy. The nature and distribution of carbon in the run products were studied by electron microprobe and time-of-flight secondary-ion mass spectroscopy (TOP-SIMS). Carbon observed by mapping with the former is clearly observed on micro-cracks that, based on the microtexture, are interpreted to have formed during the deformation. The TOF-SIMS data confirm the electron-probe observations that carbon is present on fracture surfaces. These observations and experimental results lead to the hypothesis that as microfractures open in the time leading up to failure along a fracture, carbon is deposited as a continuous film on the new, reactive mineral surfaces, and this produces a decrease in resistance. Subsequent changes in resistance occur as connectivity of the initial fracture network is altered by continued deformation. Such a process may explain some electromagnetic effects associated with earthquakes.

4D monitoring of actively failing rockslopes

NASA Astrophysics Data System (ADS)

Rosser, Nick; Williams, Jack; Hardy, Richard; Brain, Matthew

2017-04-01

Assessing the conditions which promote rockfall to collapse relies upon detailed monitoring, ideally before, during and immediately after failure. With standard repeat surveys it is common that surveys do not coincide with or capture precursors, or that surveys are widely spaced relative to the timing and duration of driving forces such as storms. As a result gaining insight into the controls on failure and the timescales over which precursors operate remains difficult to establish with certainty, and establishing direct links between environmental conditions and rock-falls, or sequences of events prior to rockfall, remain difficult to define. To address this, we present analysis of a high-frequency 3D laser scan dataset captured using a new permanently installed system developed to constantly monitor actively failing rock slopes. The system is based around a time of flight laser scanner, integrated with and remotely controlled by dedicated controls and analysis software. The system is configured to capture data at 0.1 m spacing across > 22,000 m3 at up to 30 minute intervals. Here we present results captured with this system over a period of 9 months, spanning spring to winter 2015. Our analysis is focussed upon improving the understanding of the nature of small (< 1m^3) rockfalls falling from near vertical rock cliffs. We focus here on the development of a set of algorithms for differencing that trade-off the temporal resolution of frequent surveys (hourly) against high spatial resolution point clouds (< 0.05 m) to enhance the precision of change detection, allowing both deformation and detachments to be monitored through time. From this dataset we derive rockfall volume frequency distributions based upon short-interval surveys, and identify the presence and/or absence of precursors, in what we believe to be the first constant volumetric measurement of rock face erosion. The results hold implications for understanding of rockfall mechanics, but also for how actively eroding surfaces can be monitored at high temporal frequency. Whilst high frequency data is ideal for describing processes that evolve rapidly through time, the cumulative errors that accumulate when monitored changes are dominated by inverse power-law distributed volumes are significant. To conclude we consider the benefits of defining survey frequency on the basis of the changes being detected relative to the accumulation of errors that inevitably arises when comparing high numbers of sequential surveys.

Processes and controls in swelling anhydritic clay rocks

NASA Astrophysics Data System (ADS)

Mutschler, Thomas; Blum, Philipp; Butscher, Christoph

2015-04-01

Referring to the swelling of anhydritic clay rocks in tunneling, Leopold Müller-Salzburg noted in the third volume on tunneling of his fundamental text book on rock engineering that "a truly coherent explanation of these phenomena is still owing" (Müller-Salzburg 1978, p. 306). This valuation is still true after more than three decades of research in the field of swelling anhydritic clay rocks. One of the reasons is our limited knowledge of the processes involved in the swelling of such rocks, and of the geological, mineralogical, hydraulic, chemical and mechanical controls of the swelling. In this contribution, a review of processes in swelling anhydritic clay rocks and of associated controls is presented. Also numerical models that aim at simulating the swelling processes and controls are included in this review, and some of the remaining open questions are pointed out. By focusing on process-oriented work in this review, the presentation intends to stimulate further research across disciplines in the field of swelling anhydritic clay rocks to finally get a step further in managing the swelling problem in geotechnical engineering projects. Keywords: swelling; anhydritic clay rocks; review

Distribution and features of landslides induced by the 2008 Wengchuan Earthquake, Sichuan, China

NASA Astrophysics Data System (ADS)

Chigira, M.; Xiyong, W.; Inokuchi, T.; Gonghui, W.

2009-04-01

2008 Sichuan earthquake with a magnitude of Mw 7.9 induced numerous mass movements around the fault surface ruptures of which maximum separations we observed were 3.6 m vertical and 1.5 m horizontal (right lateral). The affected area was mountainous areas with elevations from 1000 m to 4500 m on the west of the Sichuan Basin. The NE-trending Longmenshan fault zone runs along the boundary between the mountains on the west and the Sichuan basin (He and Tsukuda, 2003), of which Yinghsiuwan-Beichuan fault was the main fault that generated the 2008 earthquake (Xu, 2008). The basement rocks of the mountainous areas range from Precambrian to Cretaceous in age. They are basaltic rocks, granite, phyllite, dolostone, limestone, alternating beds of sandstone and shale, etc. There were several types of landslides ranging from small, shallow rockslide, rockfall, debris slide, deep rockslide, and debris flows. Shallow rockslide, rock fall, and debris slide were most common and occurred on convex slopes or ridge tops. When we approached the epicentral area, first appearing landslides were of this type and the most conspicuous was a failure of isolated ridge-tops, where earthquake shaking would be amplified. As for rock types, slopes of granitic rocks, hornfels, and carbonate rocks failed in wide areas to the most. They are generally hard and their fragments apparently collided and repelled to each other and detached from the slopes. Alternating beds of sandstone and mudstone failed on many slopes near the fault ruptures, including Yinghsiuwan near the epicenter. Many rockfalls occurred on cliffs, which had taluses on their feet. The fallen rocks tumbled down and mostly stopped within the talus surfaces, which is quite reasonable because taluses generally develop by this kind of processes. Many rockslides occurred on slopes of carbonate rocks, in which dolostone or dolomitic limestone prevails. Deep-seated rockslide occurred on outfacing slopes and shallow rockslide and rockfall occurred on infacing slopes. Infacing slopes generally are steeper than outfacing slopes and hence surface rocks on infacing slopes tend to be loosened by gravity. Detachment surfaces of carbonate rocks are generally not smooth surfaces but are rough surfaces with dimple-like depressions, which are made by dissolution of these rocks. This feature is one of the most important causes to induce landslide in carbonate rocks. Many gravitational deformations were observed on phyllite slopes. Landslides on the west of Beichuan city is probably of weathered phyllite, which had been preceded by gravitational deformation beforehand. Taochishan landslide in Beichuan occurred on probable outfacing slope of phyllite. The Formosat II images on Google earth indicated that this landslide was also preceded by gravitational deformation, which appeared as spur-crossing depressions with upslope-convex traces on plan. Satellite images indicated that some landslides had long lobate forms, suggesting that they were flow. One of them was Shechadientsu landslide 34 km northeast of Dujiangyan, occurring across the probable earthquake fault rupture. It was 1.5 km long with a maximum width of 250 m and an apparent friction angle of 22°. The top of this landslide area was a steep cliff of Precambrian granite, which failed to go down a small valley. The volume of the slope failure was estimated much less than the volume of the deposit. The small valley had sporadic patches of bedrock consisting of alternating beds of sandstone and mudstone of Triassic in age. The bedrock was covered by bluish grey, clayey, water-saturated debris, which was not disturbed and in turn covered by water-saturated brownish debris with rubbles. The landslide deposits had wrinkles on the surface and streaks of same color rock fragments. In addition, cross section near the distal part had clearly defined reverse grading, in which larger rubbles with a maximum diameter of 5 m concentrated at the surface part. These characteristics strongly suggest that valley-fill sediments mobilized by the earthquake and flowed down the valley, getting higher at the outer side of the valley bent. The largest landslide with an estimated volume of 1 billion m3 occurred on an outfacing carbonate rock slope, which had been preceded by gravitational deformation appearing as a ridge-top depression. The second largest one occurred on a smooth outfacing slope that had been undercut.

Rational Design of Tunnel Supports: An Interactive Graphics Based Analysis of the Support Requirements of Excavations in Jointed Rock Masses.

DTIC Science & Technology

1979-09-01

joint orientetion and joint slippage than to failure of the intact rock mass. Dixon (1971) noted the importance of including the confining influence of...dedicated computer. The area of research not covered by this investigation which holds promise for a future study is a detailed comparison of the results of...block data, type key "W". The program writes this data on Linc tapes for future retripval. This feature can be used to store the consolidated block

Physical properties of sidewall cores from Decatur, Illinois

USGS Publications Warehouse

Morrow, Carolyn A.; Kaven, Joern; Moore, Diane E.; Lockner, David A.

2017-10-18

To better assess the reservoir conditions influencing the induced seismicity hazard near a carbon dioxide sequestration demonstration site in Decatur, Ill., core samples from three deep drill holes were tested to determine a suite of physical properties including bulk density, porosity, permeability, Young’s modulus, Poisson’s ratio, and failure strength. Representative samples of the shale cap rock, the sandstone reservoir, and the Precambrian basement were selected for comparison. Physical properties were strongly dependent on lithology. Bulk density was inversely related to porosity, with the cap rock and basement samples being both least porous (

In search of ancestral Kilauea volcano

USGS Publications Warehouse

Lipman, P.W.; Sisson, T.W.; Ui, T.; Naka, J.

2000-01-01

Submersible observations and samples show that the lower south flank of Hawaii, offshore from Kilauea volcano and the active Hilina slump system, consists entirely of compositionally diverse volcaniclastic rocks; pillow lavas are confined to shallow slopes. Submarine-erupted basalt clasts have strongly variable alkalic and transitional basalt compositions (to 41% SiO2, 10.8% alkalies), contrasting with present-day Kilauea tholeiites. The volcaniclastic rocks provide a unique record of ancestral alkalic growth of an archetypal hotspot volcano, including transition to its tholeiitic shield stage, and associated slope-failure events.

Pulse fracture simulation in shale rock reservoirs: DEM and FEM-DEM approaches

NASA Astrophysics Data System (ADS)

González, José Manuel; Zárate, Francisco; Oñate, Eugenio

2018-07-01

In this paper we analyze the capabilities of two numerical techniques based on DEM and FEM-DEM approaches for the simulation of fracture in shale rock caused by a pulse of pressure. We have studied the evolution of fracture in several fracture scenarios related to the initial stress state in the soil or the pressure pulse peak. Fracture length and type of failure have been taken as reference for validating the models. The results obtained show a good approximation to FEM results from the literature.

True Triaxial Experimental Study of Rockbursts Induced By Ramp and Cyclic Dynamic Disturbances

NASA Astrophysics Data System (ADS)

Su, Guoshao; Hu, Lihua; Feng, Xiating; Yan, Liubin; Zhang, Gangliang; Yan, Sizhou; Zhao, Bin; Yan, Zhaofu

2018-04-01

A modified rockburst testing system was utilized to reproduce rockbursts induced by ramp and cyclic dynamic disturbances with a low-intermediate strain rate of 2 × 10-3-5 × 10-3 s-1 in the laboratory. The experimental results show that both the ramp and cyclic dynamic disturbances play a significant role in inducing rockbursts. In the tests of rockbursts induced by a ramp dynamic disturbance, as the static stress before the dynamic disturbance increases, both the strength of specimens and the kinetic energy of the ejected fragments first increase and then decrease. In the tests of rockbursts induced by a cyclic dynamic disturbance, there exists a rockburst threshold of the static stress and the dynamic disturbance amplitude, and the kinetic energy of the ejected fragments first increases and then decreases as the cyclic dynamic disturbance frequency increases. The main differences between rockbursts induced by ramp dynamic disturbances and those induced by cyclic dynamic disturbances are as follows: the rockburst development process of the former is characterized by an impact failure feature, while that of the latter is characterized by a fatigue failure feature; the damage evolution curve of the specimen of the former has a leap-developing form with a significant catastrophic feature, while that of the latter has an inverted S-shape with a remarkable fatigue damage characteristic; the energy mechanism of the former involves the ramp dynamic disturbance giving extra elastic strain energy to rocks, while that of the latter involves the cyclic dynamic disturbance decreasing the ultimate energy storage capacity of rocks.

Geophysical aspects of underground fluid dynamics and mineral transformation process

NASA Astrophysics Data System (ADS)

Khramchenkov, Maxim; Khramchenkov, Eduard

2014-05-01

The description of processes of mass exchange between fluid and poly-minerals material in porous media from various kinds of rocks (primarily, sedimentary rocks) have been examined. It was shown that in some important cases there is a storage equation of non-linear diffusion equation type. In addition, process of filtration in un-swelling soils, swelling porous rocks and coupled process of consolidation and chemical interaction between fluid and particles material were considered. In the latter case equations of physical-chemical mechanics of conservation of mass for fluid and particles material were used. As it is well known, the mechanics of porous media is theoretical basis of such branches of science as rock mechanics, soil physics and so on. But at the same moment some complex processes in the geosystems lacks full theoretical description. The example of such processes is metamorphosis of rocks and correspondent variations of stress-strain state. In such processes chemical transformation of solid and fluid components, heat release and absorption, phase transitions, rock destruction occurs. Extensive usage of computational resources in limits of traditional models of the mechanics of porous media cannot guarantee full correctness of obtained models and results. The process of rocks consolidation which happens due to filtration of underground fluids is described from the position of rock mechanics. As an additional impact, let us consider the porous media consolidating under the weight of overlying rock with coupled complex geological processes, as a continuous porous medium of variable mass. Problems of obtaining of correct storage equations for coupled processes of consolidation and mass exchange between underground fluid and skeleton material are often met in catagenesi processes description. The example of such processes is metamorphosis of rocks and correspondent variations of stress-strain state. In such processes chemical transformation of solid and fluid components, heat release and absorption, phase transitions, rock destruction occurs. Extensive usage of computational resources in limits of traditional models of the mechanics of porous media cannot guarantee full correctness of obtained models and results. The present work is dedicated to the retrieval of new ways to formulate and construct such models. It was shown that in some important cases there is a governing equation of non-linear diffusion equation type (well-known Fisher equation). In addition, some geophysical aspects of filtration process in usual non-swelling soils, swelling porous rocks and coupled process of consolidation and chemical interaction between fluid and skeleton material, including earth quakes, are considered.

Landslides and rock fall processes in the proglacial area of the Gepatsch glacier, Tyrol, Austria - Quantitative assessment of controlling factors and process rates

NASA Astrophysics Data System (ADS)

Vehling, Lucas; Rohn, Joachim; Moser, Michael

2013-04-01

Due to the rapid deglaciation since 1850, lithological structures and topoclimatic factors, mass movements like rock fall, landslides and complex processes are important contributing factors to sediment transport and modification of the earth's surface in the steep, high mountain catchment of the Gepatsch reservoir. Contemporary geotechnical processes, mass movement deposits, their source areas, and controlling factors like material properties and relief parameters are mapped in the field, on Orthofotos and on digital elevation models. The results are presented in an Arc-Gis based geotechnical map. All mapped mass movements are stored in an Arc-Gis geodatabase and can be queried regarding properties, volume and controlling factors, so that statistical analyses can be conducted. The assessment of rock wall retreat rates is carried out by three different methods in multiple locations, which differ in altitude, exposition, lithology and deglaciation time: Firstly, rock fall processes and rates are investigated in detail on five rock fall collector nets with an overall size of 750 m2. Rock fall particles are gathered, weighed and grain size distribution is detected by sieving and measuring the diameter of the particles to distinct between rock fall processes and magnitudes. Rock wall erosion processes like joint formation and expansions are measured with high temporal resolution by electrical crack meters, together with rock- and air temperature. Secondly, in cooperation with the other working groups in the PROSA project, rock fall volumes are determined with multitemporal terrestrial laserscanning from several locations. Lately, already triggered rock falls are accounted by mapping the volume of the deposit and calculating of the bedrock source area. The deposition time span is fixed by consideration of the late Holocene lateral moraines and analysing historical aerial photographs, so that longer term rock wall retreat rates can be calculated. In order to limit homogenous bedrock sections for calculating specific rock wall retreat rates and to extrapolate the local determinated rock wall retreat rates to larger scale, bedrock areas will be divided into units of similar morphodynamic intensities which will be therefore classified by a rock mass strength (RMS) system. The RMS-System contains lithological and topoclimatic factors but also takes the measured rock wall retreat rates into account.

Geomorphology and age of the Marocche di Dro rock avalanches (Trentino, Italy)

NASA Astrophysics Data System (ADS)

Ivy-Ochs, S.; Martin, S.; Campedel, P.; Hippe, K.; Alfimov, V.; Vockenhuber, C.; Andreotti, E.; Carugati, G.; Pasqual, D.; Rigo, M.; Viganò, A.

2017-08-01

The Marocche di Dro deposits in the lower Sarca Valley are some of the most distinctive rock avalanche deposits of the Alps. We use geomorphology and cosmogenic 36Cl exposure dating of boulders to divide the Marocche di Dro deposits into two rock avalanche bodies; the Marocca Principale to the north and the Kas to the south. The deposits were previously undated and had been mapped as up to five different events. The largest event Marocca Principale, which comprises an estimated 1000 106 m3 of predominantly Rotzo Formation limestones, occurred 5300 ± 860 yr ago. The release area is located mainly in the alcove between Mt. Casale and Mt. Granzoline, but likely extends all the way to Mt. Brento. The Kas event took place 1080 ± 160 yr ago with detachment below Mt. Brento. The Kas debris, with an estimated volume of 300 106 m3, buried the southern third of the Marocca Principale deposit. Kas presents a barren, stark landscape dominated by house-sized Tovel Member Rotzo Formation boulders bearing distinctive chert lenses. Both the extreme relief of the rock wall (more than 1300 m) and the tectonic setting predispose the range front to massive failure. For the two events, initially translational movement likely quickly evolved into complex failure and massive collapse. Run-out across the valley of several kilometers and run-up on the opposite slope of hundreds of meters followed. A summary of all dated and large historical landslides in the Alps underlines the periods of enhanced slope activity discussed in the literature: 10-9 kyr, 5-3 kyr, and 2-1 kyr, the latter especially for the Southern Alps. No deposits of the first temporal cluster are found at Marocche di Dro. The age of Marocca Principale at 5300 ± 860 yr suggests occurrence during the second period. Failure may have been related to the shift to wetter, colder climate at the transition from the middle to the late Holocene. Nevertheless, a seismic trigger cannot be ruled out. For the Kas rock avalanche at 1080 ± 160 yr ago we implicate the ;Middle Adige Valley; (1046 CE) earthquake as trigger. Its epicentral distance is much closer to the Sarca Valley in comparison to that of the Verona earthquake (1117 CE).

Process and Energy Optimization Assessment, Rock Island Arsenal, IL

DTIC Science & Technology

2004-09-01

Approved for public release; distribution is unlimited. ER D C /C ER L TR -0 4- 17 Process and Energy Optimization Assessment Rock Island... Optimization Assessment: Rock Island Arsenal, IL Mike C.J. Lin, Alexander M. Zhivov, and Veera M. Boddu, Construction Engineering Research...and Energy Optimization Assessment (PEOA) was conducted at Rock Island Arsenal (RIA), IL to identify process, energy, and environmental opportunities

Pristine nonmare rocks and the nature of the lunar crust

NASA Technical Reports Server (NTRS)

Warren, P. H.; Wasson, J. T.

1977-01-01

It is shown that the interdisciplinary study of the nonmare lunar rocks based on trace element, major element, and isotopic data plus petrographic evidence can succeed in amassing a large suite of demonstrably pristine rocks, and that the relative numbers of these rocks are not in accord with statistics amassed on soil fragments and glasses. The term 'pristine' is taken to mean rocks with primary compositions (albeit not necessarily textures) produced by lunar endogenous igneous processes. Melt rocks and crystalline matrix breccias produced by impact processes are excluded. A petrographic synonym for pristine would be 'unremelted, monomict'. It is found that anorthositic norites and noritic anorthosites were rare as primary nonmare rocks. Mechanical mixing appears to have been the dominant petrogenetic process on the highlands.

Early Holocene (8.6 ka) rock avalanche deposits, Obernberg valley (Eastern Alps): Landform interpretation and kinematics of rapid mass movement.

PubMed

Ostermann, Marc; Sanders, Diethard; Ivy-Ochs, Susan; Alfimov, Vasily; Rockenschaub, Manfred; Römer, Alexander

2012-10-15

In the Obernberg valley, the Eastern Alps, landforms recently interpreted as moraines are re-interpreted as rock avalanche deposits. The catastrophic slope failure involved an initial rock volume of about 45 million m³, with a runout of 7.2 km over a total vertical distance of 1330 m (fahrböschung 10°). 36 Cl surface-exposure dating of boulders of the avalanche mass indicates an event age of 8.6 ± 0.6 ka. A 14 C age of 7785 ± 190 cal yr BP of a palaeosoil within an alluvial fan downlapping the rock avalanche is consistent with the event age. The distal 2 km of the rock-avalanche deposit is characterized by a highly regular array of transverse ridges that were previously interpreted as terminal moraines of Late-Glacial. 'Jigsaw-puzzle structure' of gravel to boulder-size clasts in the ridges and a matrix of cataclastic gouge indicate a rock avalanche origin. For a wide altitude range the avalanche deposit is preserved, and the event age of mass-wasting precludes both runout over glacial ice and subsequent glacial overprint. The regularly arrayed transverse ridges thus were formed during freezing of the rock avalanche deposits.

An Elasto-Plastic Damage Model for Rocks Based on a New Nonlinear Strength Criterion

NASA Astrophysics Data System (ADS)

Huang, Jingqi; Zhao, Mi; Du, Xiuli; Dai, Feng; Ma, Chao; Liu, Jingbo

2018-05-01

The strength and deformation characteristics of rocks are the most important mechanical properties for rock engineering constructions. A new nonlinear strength criterion is developed for rocks by combining the Hoek-Brown (HB) criterion and the nonlinear unified strength criterion (NUSC). The proposed criterion takes account of the intermediate principal stress effect against HB criterion, as well as being nonlinear in the meridian plane against NUSC. Only three parameters are required to be determined by experiments, including the two HB parameters σ c and m i . The failure surface of the proposed criterion is continuous, smooth and convex. The proposed criterion fits the true triaxial test data well and performs better than the other three existing criteria. Then, by introducing the Geological Strength Index, the proposed criterion is extended to rock masses and predicts the test data well. Finally, based on the proposed criterion, a triaxial elasto-plastic damage model for intact rock is developed. The plastic part is based on the effective stress, whose yield function is developed by the proposed criterion. For the damage part, the evolution function is assumed to have an exponential form. The performance of the constitutive model shows good agreement with the results of experimental tests.

High-resolution seismic monitoring of rockslide activity in the Illgraben, Switzerland

NASA Astrophysics Data System (ADS)

Burtin, Arnaud; Hovius, Niels; Dietze, Michael; McArdell, Brian

2014-05-01

Rockfalls and rockslides are important geomorphic processes in landscape dynamics. They contribute to the evolution of slopes and supply rock materials to channels, enabling fluvial incision. Hillslope processes are also a natural hazard that we need to quantify and, if possible, predict. For these reasons, it is necessary to determine the triggering conditions and mechanisms involved in rockfalls. Rainfall is a well-known contributor since water, through soil moisture or pore pressure, may lead to the inception and propagation of cracks and can induce slope failure. Water can also affect slope stability through effects of climatic conditions such as the fluctuations of temperature around the freezing point. During the winter of 2012, we have recorded with a seismic array of 8 instruments substantial rockslide activity that affected a gully in the Illgraben catchment in the Swiss Alps. Three stations were positioned directly around the gully with a nearest distance of 400 m. The period of intense activity did not start during a rainstorm as it is common in summer but during a period of oscillation of temperatures around the freezing point. The activity did not occur in a single event but lasted about a week with a decay in time of the event frequency. Many individual events had two distinct seismic signals, with first, a short duration phase of about 10 s at frequencies below 5 Hz that we interpret as a slope failure signature, followed by a second long duration signal of > 60 s at frequencies above 10 Hz that we attribute to the propagation of rock debris down the slope. Thanks to the array of seismic sensors, we can study the fine details of this rockslide sequence by locating the different events, determining their distribution in time, and systematic quantification of seismic metrics (energy, duration, intensity...). These observations are compared to independent meteorological constrains and laser scan data to obtain an estimate of the volume mobilized by the event.

On the Processing of Spalling Experiments. Part I: Identification of the Dynamic Tensile Strength of Concrete

NASA Astrophysics Data System (ADS)

Forquin, P.; Lukić, B.

2017-11-01

The spalling technique based on the use of a single Hopkinson bar put in contact with the tested sample has been widely adopted as a reliable method for obtaining the tensile response of concrete and rock-like materials at strain rates up-to 200 s- 1. However, the traditional processing method, based on the use of Novikov acoustic approach and the rear face velocity measurement, remains quite questionable due to strong approximations of this data processing method. Recently a new technique for deriving cross-sectional stress fields of a spalling sample filmed with an ultra-high speed camera and based on using the full field measurements and the virtual fields method (VFM) was proposed. In the present work, this topic is perused by performing several spalling tests on ordinary concrete at high acquisition speed of 1Mfps to accurately measure the tensile strength, Young's modulus, strain-rate at failure and stress-strain response of concrete at high strain-rate. The stress-strain curves contain more measurement points for a more reliable identification. The observed tensile stiffness is up-to 50% lower than the initial compressive stiffness and the obtained peak stress was about 20% lower than the one obtained by applying the Novikov method. In order to support this claim, numerical simulations were performed to show that the change of stiffness between compression and tension highly affects the rear-face velocity profile. This further suggests that the processing based only on the velocity "pullback" is quite sensitive and can produce an overestimate of the tensile strength in concrete and rock-like materials.

Determination of the mechanical parameters of rock mass based on a GSI system and displacement back analysis

NASA Astrophysics Data System (ADS)

Kang, Kwang-Song; Hu, Nai-Lian; Sin, Chung-Sik; Rim, Song-Ho; Han, Eun-Cheol; Kim, Chol-Nam

2017-08-01

It is very important to obtain the mechanical paramerters of rock mass for excavation design, support design, slope design and stability analysis of the underground structure. In order to estimate the mechanical parameters of rock mass exactly, a new method of combining a geological strength index (GSI) system with intelligent displacment back analysis is proposed in this paper. Firstly, average spacing of joints (d) and rock mass block rating (RBR, a new quantitative factor), surface condition rating (SCR) and joint condition factor (J c) are obtained on in situ rock masses using the scanline method, and the GSI values of rock masses are obtained from a new quantitative GSI chart. A correction method of GSI value is newly introduced by considering the influence of joint orientation and groundwater on rock mass mechanical properties, and then value ranges of rock mass mechanical parameters are chosen by the Hoek-Brown failure criterion. Secondly, on the basis of the measurement result of vault settlements and horizontal convergence displacements of an in situ tunnel, optimal parameters are estimated by combination of genetic algorithm (GA) and numerical simulation analysis using FLAC3D. This method has been applied in a lead-zinc mine. By utilizing the improved GSI quantization, correction method and displacement back analysis, the mechanical parameters of the ore body, hanging wall and footwall rock mass were determined, so that reliable foundations were provided for mining design and stability analysis.

Rock cliffs hazard analysis based on remote geostructural surveys: The Campione del Garda case study (Lake Garda, Northern Italy)

NASA Astrophysics Data System (ADS)

Ferrero, A. M.; Migliazza, M.; Roncella, R.; Segalini, A.

2011-02-01

The town of Campione del Garda (located on the west coast of Lake Garda) and its access road have been historically subject to rockfall phenomena with risk for public security in several areas of the coast. This paper presents a study devoted to the determination of risk for coastal cliffs and the design of mitigation measures. Our study was based on statistical rockfall analysis performed with a commercial code and on stability analysis of rock slopes based on the key block method. Hazard from block kinematics and rock-slope failure are coupled by applying the Rockfall Hazard Assessment Procedure (RHAP). Because of the huge dimensions of the slope, its morphology and the geostructural survey were particularly complicated and demanding. For these reasons, noncontact measurement methods, based on aerial photogrammetry by helicopter, were adopted. A special software program, developed by the authors, was applied for discontinuity identification and for their orientation measurements. The potentially of aerial photogrammetic survey in rock mechanic application and its improvement in the rock mass knowledge is analysed in the article.

Rockfall hazard mapping along a mountainous road in Switzerland using a GIS-based parameter rating approach

NASA Astrophysics Data System (ADS)

Baillifard, F.; Jaboyedoff, M.; Sartori, M.

A posteriori studies of rock slope instabilities generally show that rockfalls do not occur at random locations: the failure zone can be classified as sensitive from geomorphological evidence. Zones susceptible to failure can there-fore be detected. Effects resulting from degrading and triggering factors, such as groundwater circulation and freeze and thaw cycles, must then be assessed in order to evaluate the probability of failure. A simple method to detect rock slope instabilities was tested in a study involving a 2000 m3 rockfall that obstructed a mountainous road near Sion (Switzerland) on 9 January 2001. In order to locate areas from which a rock-fall might originate, areas were assessed with respect to the presence or absence of five criteria: (1) a fault, (2) a scree slope within a short distance, (3) a rocky cliff, (4) a steep slope, and (5) a road. These criteria were integrated into a Geographic Information System (GIS) using existing topo-graphic, geomorphological, and geological vector and raster digital data. The proposed model yields a rating from 0 to 5, and gives a relative hazard map. Areas yielding a high relative hazard have to meet two additional criteria if they are to be considered as locations from which a rockfall might originate: (1) the local structural pattern has to be unfavourable, and (2) the morphology has to be susceptible to the effects of degrading and triggering factors. The rockfall of 9 January 2001, has a score of 5. Applied to the entire length of the road (4 km), the present method reveals two additional areas with a high relative hazard, and allows the detection of the main instabilities of the site.

Using street view imagery for 3-D survey of rock slope failures

NASA Astrophysics Data System (ADS)

Voumard, Jérémie; Abellán, Antonio; Nicolet, Pierrick; Penna, Ivanna; Chanut, Marie-Aurélie; Derron, Marc-Henri; Jaboyedoff, Michel

2017-12-01

We discuss here different challenges and limitations of surveying rock slope failures using 3-D reconstruction from image sets acquired from street view imagery (SVI). We show how rock slope surveying can be performed using two or more image sets using online imagery with photographs from the same site but acquired at different instances. Three sites in the French alps were selected as pilot study areas: (1) a cliff beside a road where a protective wall collapsed, consisting of two image sets (60 and 50 images in each set) captured within a 6-year time frame; (2) a large-scale active landslide located on a slope at 250 m from the road, using seven image sets (50 to 80 images per set) from five different time periods with three image sets for one period; (3) a cliff over a tunnel which has collapsed, using two image sets captured in a 4-year time frame. The analysis include the use of different structure from motion (SfM) programs and a comparison between the extracted photogrammetric point clouds and a lidar-derived mesh that was used as a ground truth. Results show that both landslide deformation and estimation of fallen volumes were clearly identified in the different point clouds. Results are site- and software-dependent, as a function of the image set and number of images, with model accuracies ranging between 0.2 and 3.8 m in the best and worst scenario, respectively. Although some limitations derived from the generation of 3-D models from SVI were observed, this approach allowed us to obtain preliminary 3-D models of an area without on-field images, allowing extraction of the pre-failure topography that would not be available otherwise.