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Comparison of six major intact rock failure criteria using a particle flow approach under true-triaxial stress condition

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GEOMECHANICS AND GEOPHYSICS FOR GEO-ENERGY AND GEO-RESOURCES 2016年第4期2卷 203-229页

作者： Mehranpour, Mohammad Hadi Kulatilake, Pinnaduwa H. S. W. Univ Arizona Rock Mass Modeling & Computat Rock Mech Labs Tucson AZ 85721 USA

Suitability of six major intact rock failure criteria: Mohr-Coulomb, Hoek-Brown, Modified Lade, Modified Wiebols and Cook, Mogi and Drucker-Prager in representing the intact rock strength under the true-triaxial stress condition (sigma(1) >= sigma(2) >= sigma(3)) is examined in this paper. Because the true-triaxial experimental test data available in the literature are limited and do not cover a wide range of confining stresses, the particle flow code (PFC3D) software was used to simulate synthetic rock material failure of cubic samples of side dimension 160 mm under a broad confining stress range. The synthetic rock was made out of a mixture of gypsum, sand and water. The parallel bond model (PBM) available in PFC3D with the associated micro parameters was chosen to represent the behavior of the synthetic material. As the first step, uniaxial, triaxial and Brazilian tests were performed in the laboratory to find the macro properties of the synthetic material. As the second step, the effect of some of the micro properties: particle size, coefficient of variation of the normal and shear bond strengths and friction coefficient on the macro properties of the synthetic rock was investigated. Then, the micro parameters of PBM were calibrated based on the aforementioned macro parameter results. Using the calibrated PFC3D model 29 true-triaxial tests were simulated. All six failure criteria were fitted to these PFC data. Among these criteria, Modified Lade, Mogi and Modified Wiebols and Cook found to be the best failure criteria producing lower root mean square error (RMSE) values of 0.212, 0.219 and 0.304, respectively. Thus those three criteria are recommended for prediction of intact rock strength under true-triaxial stress condition. Another fitting analysis was conducted using only 12 of the 29 data to find the effect of the limited data on the prediction accuracy of the three failure criteria through the RMSE value. The predictions based on these analyses produced RM

关键词： Rock failure criteria True-triaxial Polyaxial Numerical modeling Discrete element method particle flow code

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Numerical simulation of mechanical characteristics of jointed rock in direct shear test

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ROCK AND SOIL MECHANICS 2016年第2期37卷 583-591页

作者： Li Xiao-feng Li Hai-bo Xia Xiang Liu Bo Feng Hai-peng Chinese Acad Sci Inst Rock & Soil Mech State Key Lab Geomech & Geotech Engn Wuhan 430071 Hubei Peoples R China China Guangdong Nucl Power Stn Engn Co Ltd Shenzhen 518124 Guangdong Peoples R China

The stability of rock engineering is strongly dependent on the shear strength of jointed rock mass. Based on the particle flow code (PFC2D), the reasonable mesoscopic parameters are selected in combination with experimental results to analyze the meso-properties of crack propagation, energy transmission, and acoustic emission phenomenon of jointed rock. The strength models and failure patterns of jointed rock are numerically simulated. The main research results are summarized as follows. Abrasive and shear failure patterns heavily exist in jointed rock, and different failure patterns are corresponding to different strength models. Rock mass is damaged along joint plane with the increase of shear deformation. Normal cracks prevail within elastic stage, whereas shear cracks dominate along the rough surface within plastic stage. The joint plane slides owing to appearance of crushed zone induced by the coalescence of R and P cracks. Boundary energy is mainly converted into strain energy and more normal cracks are generated prior to the peak shear strength. With the increase of shear stress, the friction energy grows rapidly and a large amount of shear cracks are produced at the same time. Compared with experiments, PFC2D can be used to simulate the shear properties of jointed rock mass well, which remedies the challenge of simulating behaviors of jointed rock at meso-scale in the laboratory test and provides a useful reference for further research on direct shear tests of jointed rock mass.

关键词： jointed rock joint direct shear test particle flow code crack evolution

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Study of seismic response of colluvium accumulation slope by particle flow code

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GRANULAR MATTER 2010年第5期12卷 483-490页

作者： He, Jianming Li, Xiao Li, Shouding Yin, Yueping Qian, Haitao Chinese Acad Sci Inst Geol & Geophys Key Lab Engn Geomech Beijing 100029 Peoples R China China Earthquake Adm Inst Crustal Dynam Beijing 100085 Peoples R China China Geol Survey Beijing 100037 Peoples R China

Colluvium accumulation slopes (CAS) are widely distributed in Sichuan Province of China, especially in the regions with intense earthquake histories. These kinds of accumulations show obvious discontinuous and heterogeneous characteristics, to which the discrete element method (DEM) for discontinuous material is more suitably applied. Wenchuan earthquake with a magnitude of 8.0, caused a large number of debris flows or landslides in the colluvium formations, which are densely distributed in the quake-hit region in Sichuan province. The dynamic response of CAS is a key problem for study of stability of these kinds of slope. In this paper, PFC (particle flow code) from Itasca based on DEM is used for modeling the dynamic response of the colluvium accumulations and some typical models were built according to the geological investigations carried out in the epicentral area. Horizontal shearing waveforms of WenChuan earthquake were input into the model for the study of the dynamic response of overlying colluvium accumulation and bedrock. The modeling results of different models under the same seismic conditions are described and analyzed at the end of the paper.

关键词： Colluvium accumulation slope (CAS) Dynamic response particle flow code Discontinuous characteristics

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Numerical Simulation of Shear Behaviour of Non-Persistent Joints under Low and High Normal Loads

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PERIODICA POLYTECHNICA-CIVIL ENGINEERING 2016年第4期60卷 517-529页

作者： Sarfarazi, Vahab Ghazvinian, Abdolhadi Schubert, Wulf Hamedan Univ Technol Dept Min Engn Mardom StPOB 65155-579 Hamadan Iran Tarbiat Modares Univ Dept Min Engn Gisha StPOB 14115-111 Tehran Iran Graz Univ Technol Inst Rock Mech & Tunnelling Rechbauerstr 12 A-8010 Graz Austria

In this paper, the effect of rock bridge surface on the shear behavior of planar non-persistent joints under low and high normal loads has been investigated using particle flow code in 2 Dimensions. PFC2d was calibrated with respect to the data obtained from experimental laboratory tests to ensure the conformity of the simulated numerical models response. The models consisting non-persistent joint were simulated and tested by shear loading under low and high normal loads. The discrete element simulations demonstrated that the failure pattern was mostly influenced by normal load, while the shear strength was linked to the failure pattern and failure mechanism. The failure patterns were found reasonably similar to the experimentally observed trends.

关键词： particle flow code joint separation normal load shear and tensile cracks

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Deformation Characteristics and Stress Distribution of Filling Body and Coal Pillar in Backfill-strip Mining

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ELECTRONIC JOURNAL OF GEOTECHNICAL ENGINEERING 2016年第6期21卷 2455-2466页

作者： Zhu Xiaojun Guo Guangli Yang Xiaoyu Chen Tao China Univ Min & Technol Key Lab Land Environm & Disaster Monitoring SBSM Xuzhou Jiangsu Peoples R China

In consideration of currently high filling costs and backfill material shortage, backfill-strip mining was proposed, which combines the advantages of strip-partial mining and backfilling mining In the mining technology, longwall partial backfilling mining is firstly conducted, then residual coal pillar is recycled, and eventually a combined support structure of filling body and coal pillar (CSSFC for short) is formed to support the overlying strata. The stability of CSSFC is the key factor to the success of strata control in backfill-strip mining In this paper, particle flow code is used to conduct in-depth research into the stress distribution, deformation characteristics and failure behaviours of CSSFC. The study can provide a scientific reference for safety mining design of backfill-strip mining as well as prevent surface subsidence disasters.

关键词： backfilling-strip mining particle flow code strata control combined support structure of filling body and coal pillar

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Numerical simulation of drilling-induced core damage and its influence on mechanical properties of rocks under unconfined condition

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INTERNATIONAL JOURNAL OF ROCK MECHANICS AND MINING SCIENCES 2015年 80卷 40-50页

作者： Bahrani, Navid Valley, Benoit Kaiser, Peter K. MIRARCO Geomech Res Ctr Sudbury ON Canada Laurentian Univ Bharti Sch Engn Sudbury ON P3E 2C6 Canada Univ Neuchatel Ctr Hydrogeol & Geotherm CH-2000 Neuchatel Switzerland

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Characterization of strength and damage of hard rock pillars using a synthetic rock mass method

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COMPUTERS AND GEOTECHNICS 2015年 65卷 56-72页

作者： Zhang, Y. Stead, D. Elmo, D. Northeastern Univ Min Engn Dept Shenyang Peoples R China Simon Fraser Univ Dept Earth Sci Burnaby BC V5A 1S6 Canada Univ British Columbia NBK Min Dept Vancouver BC V5Z 1M9 Canada

In this research a 3D Synthetic Rock Mass (SRM) method is used to numerically characterize the strength and damage of hard rock pillars. The SRM is an integrated model incorporating a Discrete Fracture Network (DFN) within a particle flow code 3D (PFC3D) particle assembly. Based on the numerical results of a joint-free pillar model, laterally fixed loading platens are suggested to simulate uniaxial compression tests on rock pillars. An internal-strain loading method is meanwhile used to ensure more realistic model behaviour. The peak strength, post-peak strain-softening gradient and deformation modulus of a series of jointed pillar models are then quantified, in order to investigate the effects of the inserted joint sets. The simulated peak strengths demonstrate a U-shape relationship when the joint sets are rotated;the peak strength also decreases with increasing joint size. A brittle post-peak behaviour is observed for pillar models with vertical joint sets of low persistence, the post-peak behaviour becoming more ductile when the joint sets are inclined and of higher persistence. A correlation is identified between the post-peak pillar behaviour and the simulated tensile cracking events, where a brittle post-peak corresponds to a high cracking rate. The effects of the joint sets on the pillar deformation modulus are observed to be similar to the effects on the pillar peak strength. Particular attention is given to the characterization of the crack initiation stress (sigma(ci)) and crack damage stress (sigma(cd)) thresholds of each pillar model, where the ratio of the crack initiation stress/peak strength is between 03 and 0.45, and the ratio of the crack damage stress/peak strength is between 0.75 and 0.98. The simulated cracks are compared between the jointed pillars and detailed cracking modes are plotted as 3D views and as 2D thin layers for selected pillar models. (C) 2014 Elsevier Ltd. All rights reserved.

关键词： Hard rock pillar Joint set effect Synthetic rock mass particle flow code Discrete Fracture Network

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Numerical investigation on optimized stimulation of intact and naturally fractured deep geothermal reservoirs using hydro-mechanical coupled discrete particles joints model

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GEOTHERMICS 2014年 52卷 165-184页

作者： Yoon, Jeoung Seok Zang, Arno Stephansson, Ove GFZ German Res Ctr Geosci Helmholtz Ctr Potsdam Sect Seism Hazard & Stress Field 2 6 D-14473 Potsdam Germany

This numerical study investigates hydraulic fracturing and induced seismicity in intact and fractured reservoirs under anisotropic in situ stress using hydro-mechanical coupled discrete particles joints model. A 2 km x 2 km reservoir model with granitic rock and joints properties is constructed. Various injection scenarios are tested which involve continuous and cyclic styles of pressure controlled and flow rate controlled injections. Results are compared which include: spatial and temporal evolution of induced seismic events in relation with fluid pressure distribution, moment magnitudes of the induced events, occurrence of post-shut-in large magnitude events, etc. Several field observations on induced seismicity phenomena are simulated which include creation of new fractures, re-activation of the pre-existing joints, post-shut-in seismicity and large magnitude event with non-double-couple source, Kaiser phenomenon, moment magnitude vs. frequency distribution of the induced events following the Gutenberg-Richter law, etc. Cyclic injection results in larger volume of injected fluid but less number of total events and larger magnitude events;hence less seismic energy radiated by the induced events, slower relaxation of the fluid pressure after shut-in, longer and thinner propagated fractures with larger fluid saturated area. The major conclusions of this study are that the presented modeling is capable of simulating induced seismicity phenomena in Enhanced Geothermal System and fluid injection in fractured reservoirs in cyclic way has potential in mitigating the effects of larger magnitude induced events. (C) 2014 Elsevier Ltd. All rights reserved.

关键词： Reservoir stimulation Fluid injection Induced seismicity Discrete particle joints model particle flow code Soft stimulation

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Scale effect on the shear behaviour of rock joints based on a numerical study

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ENGINEERING GEOLOGY 2014年 181卷 212-223页

作者： Bahaaddini, M. Hagan, P. C. Mitra, R. Hebblewhite, B. K. UNSW Australia Sch Min Engn Sydney NSW Australia Shahid Bahonar Univ Kerman Kerman Iran

A large number of studies have been carried out to investigate the effect of scale on the shear behaviour of rock joints. However, the nature of scale dependency of rock joints is still unknown and remains an ongoing debate. This paper investigates the effect of joint length on the shear behaviour of rough rock joints using PFC2D. In this numerical approach, the intact material is simulated by a dense packing of bonded particles and the joint is represented by micro-scale slip surfaces at contacts between particles. The validity of this numerical approach in reproducing the shear behaviour of rock joints has been studied in previous studies of authors against the physical experiments, analytical and empirical models. In this study, numerical direct shear tests on a natural tensile joint and subdivided joints were carried out and the shear behaviour of these joints at different scale was investigated. Results of this study show that as the joint length increases, the peak shear strength, peak dilation rate and shear stiffness decrease while the peak shear displacement increases. In order to find out the reason of observed scale dependency, the mechanism of asperity degradation at different scales was investigated and it was found that the mobilisation of different sized asperities at different scales resulted in the observed scale effect. (C) 2014 Elsevier B.V. All rights reserved.

关键词： Scale effect Rock joint Shear behaviour Joint roughness particle flow code

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Numerical direct shear tests to model the shear behaviour of rock joints

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COMPUTERS AND GEOTECHNICS 2013年 51卷 101-115页

作者： Bahaaddini, M. Sharrock, G. Hebblewhite, B. K. Univ New S Wales Sch Min Engn Sydney NSW Australia Shahid Bahonar Univ Kerman Kerman Iran

In this paper, the shear behaviour of rock joints are numerically simulated using the discrete element code PFC2D. In PFC, the intact rock is represented by an assembly of separate particles bonded together where the damage process is represented by the breakage of these bonds. Traditionally, joints have been modelled in PFC by removing the bonds between particles. This approach however is not able to reproduce the sliding behaviour of joints and also results in an unrealistic increase of shear strength and dilation angle due to the inherent micro-scale roughness of the joint surface. Modelling of joints in PFC was improved by the emergence of the smooth joint model. In this model, slip surfaces are applied to contacts between particles lying on the opposite sides of a joint plane. Results from the current study show that this method suffers from particle interlocking which takes place at shear displacements greater than the minimum diameter of the particles. To overcome this problem, a new shear box genesis approach is proposed. The ability of the new method in reproducing the shear behaviour of rock joints is investigated by undertaking direct shear tests on saw-tooth triangular joints with base angles of 15, 25 and 35 and the standard joint roughness coefficient profiles. A good agreement is found between the results of the numerical models and the Patton, Ladanyi and Archambault and Barton and Choubey models. The proposed model also has the ability to track the damage evolution during the shearing process in the form of tensile and shear fracturing of rock asperities. (C) 2013 Elsevier Ltd. All rights reserved.

关键词： Direct shear test Rock joint particle flow code Bonded particle model Smooth joint model

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