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PFC2D Simulation on Stability of Loose Deposits Slope in Highway Cutting Excavation

GEOTECHNICAL AND GEOLOGICAL ENGINEERING 2017年第2期35卷 897-902页

作者： Meng, Yun-wei China Merchants Chongqing Commun Technol Res & De Branch Highway & Geotech Engn Chongqing 400067 Peoples R China

PFC2D (particle flow code in two dimensions) is applied to simulate the stability of loose deposits slope during highway cutting excavation. In the PFC, the structure of loose deposits slope is simulated by numerous balls, which have different properties such as radius, friction coefficient, bonding strength. Different bonding strength of balls and slope ratio of highway cutting excavation are considered. A number of numerical models are set up. The particles motion pattern and impact of excavations are investigated during the cutting excavation simulation. The relationship between impact of excavations and mechanical parameters of particles, ratio of excavation is explained. The parameters of particles are corresponding to mechanical characteristics of loose deposits slope, and the impact of excavations is deeply inclined with the collapse. The method can be used for choosing the style of treatment engineering during highway cutting in loose deposits area from the mesoscopic view.

关键词： Loose deposits slope Stability Excavation ratio particle flow code

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Accident Investigation of Mine Subsidence with Application of particle flow code

Accident Investigation of Mine Subsidence with Application o...

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1st International Symposium on Mine Safety Science and Engineering (ISMSSE)

作者： Li Zhao Wang Jin-an Univ Sci & Technol Beijing State Key Lab High Efficient Min & Safety Met Min Minist Educ Beijing 100083 Peoples R China

ISBN: (纸本)9781627485821

The mine subsidence happened in Shandong province will be investigated and analyzed as a case study. According to the field survey study, the numerical model is established with PFC. Determining the micromechanics of rock parameters by uniaxial testing, the meso-structural features of rock and soil and the macro-mechanical response of those are linked. The model simulates the process of subside and calculates the distribution of contact force and displacement of ore particles, which have a good consistency in comparison with the actual survey data. Thus this method used into the mechanical analysis of collapse process, the displacement of ore and rock and so on, is effective. (C) 2011 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of China Academy of Safety Science and Technology, China University of Mining and Technology(Beijing), McGill University and University of Wollongong.

关键词： particle flow code numerical simulation mine subsidence

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Dynamic behavior of rock during its post failure stage in SHPB tests

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Transactions of Nonferrous Metals Society of China 2017年第1期27卷 184-196页

作者：周子龙赵源江益辉邹洋蔡鑫李地元中南大学资源与安全工程学院长沙410083 中国中铁工程设计咨询集团有限公司北京100000 Ecole Polytechnique Fédérale de Lausanne(EPFL) School of ArchitectureCivil and Environmental EngineeringLausanne CH-1015Switzerland

In order to investigate the micro-process and inner mechanism of rock failure under impact loading, the laboratory tests were carried out on an improved split Hopkinson pressure bar （SHPB） system with synchronized measurement devices including a high-speed camera and a dynamic strain meter. The experimental results show that the specimens were in the state of good stress equilibrium during the post failure stage even when visible cracks were forming in the specimens. Rock specimens broke into strips but still could bear the external stress and keep force balance. Meanwhile, numerical tests with particle flow code （PFC） revealed that the failure process of rocks can be described by the evolution of micro-fractures. Shear cracks emerged firstly and stopped developing when the external stress was not high enough. Tensile cracks, however, emerged when the rock specimen reached its peak strength and played an important role in controlling the ultimate failure during the post failure stage.

关键词： rock dynamics post failure stress equilibrium crack evolution particle flow code

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Investigation of the Quasi-Brittle Failure of Alashan Granite Viewed from Laboratory Experiments and Grain-Based Discrete Element Modeling

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MATERIALS 2017年第7期10卷 835-835页

作者： Zhou, Jian Zhang, Luqing Yang, Duoxing Braun, Anika Han, Zhenhua Chinese Acad Sci Inst Geol & Geophys Key Lab Shale Gas & Geoengn Beijing 100029 Peoples R China China Earthquake Adm Inst Crustal Dynam Beijing 100085 Peoples R China Univ Chinese Acad Sci Coll Earth Sci Beijing 100049 Peoples R China

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.

关键词： grain-based approach petrographic texture grain scale effect laboratory experiment particle flow code Alashan granite

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Investigation of Processes of Interaction between Hydraulic and Natural Fractures by PFC Modeling Comparing against Laboratory Experiments and Analytical Models

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ENERGIES 2017年第7期10卷 1001-1001页

作者： Zhou, Jian Zhang, Luqing Braun, Anika Han, Zhenhua Chinese Acad Sci Inst Geol & Geophys Key Lab Shale Gas & Geoengn Beijing 100029 Peoples R China Univ Chinese Acad Sci Coll Earth Sci Beijing 100049 Peoples R China

Hydraulic fracturing technology is usually used to stimulate tight gas reservoirs for increasing gas production. The stimulated volume depends in part on the pre-existing natural fractures in a reservoir. The mechanisms influencing the interaction between hydraulic fractures and natural fractures have to be well understood in order to achieve a successful application of hydraulic fracturing. In this paper, hydraulic fracturing simulations were performed based on a two-dimensional particle flow code with an embedded Smooth Joint Model to investigate the interactions between hydraulic fractures and natural fractures and compare these against laboratory experimental results and analytical models. Firstly, the ability of the Smooth Joint Model to mimic the natural rock joints was validated. Secondly, the interactions between generated hydraulic fractures and natural fractures were simulated. Lastly, the influence of angle of approach, in situ differential stress, and the permeability of natural fractures was studied. It is found that the model is capable of simulating the variety of interactions between hydraulic fractures and natural fractures such as Crossed type, Arrested type and Dilated type, and the modeling examples agree well with the experimental results. Under high approach angles and high differential stresses, the hydraulic fractures tend to cross pre-existing natural fractures. Under contrary conditions, a hydraulic fracture is more likely to propagate along the natural fracture and re-initiate at a weak point or the tip of the natural fracture. Moreover, these numerical results are in good agreement compared with Blanton's criterion. The variety of permeability of natural fractures has a great effect on their interactions, which should not be overlooked in hydraulic fracturing studies.

关键词： hydraulic fracturing natural fracture laboratory experiment numerical simulation particle flow code smooth joint model

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Accident Investigation of Mine Subsidence with Application of particle flow code

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Procedia Engineering 2011年 26卷 1698-1704页

作者： Li Zhao Wang Jin-an State Key Laboratory of High-efficient Mining and Safety of Metal Mines Ministry of Education University of Science and Technology Beijing Beijing 100083 China School of Civil and Environmental Engineering University of Science and Technology Beijing Beijing 100083 China

关键词： particle flow code numerical simulation mine subsidence

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Numerical simulation of rock fragmentation mechanisms subject to wedge penetration for TBMs

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TUNNELLING AND UNDERGROUND SPACE TECHNOLOGY 2016年 53卷 96-108页

作者： Li, X. F. Li, H. B. Liu, Y. Q. Zhou, Q. C. Xia, X. Chinese Acad Sci Inst Rock & Soil Mech State Key Lab Geomech & Geotech Engn Wuhan 430071 Peoples R China

The rock fragmentation mechanism and failure process induced by a wedge indenter for TBMs are numerically simulated utilizing the discrete element method (DEM) in the present study. A novel clustered assembly approach with irregular boundaries for grain-based brittle rock is incorporated into the particle flow code (PFC) to calibrate the macro-responses such as the low tensile to compressive strength ratio observed in laboratory tests. The simulation results are compared with laboratory tests which were conducted to reveal the rock indentation process and rock-tool interactions. The numerical analysis can be divided to two main parts. Part one is to investigate the crack propagation and damage evolution at meso-scale associated with the force-indentation curve. The stress field distributions with respect to indentation time are depicted. It is revealed that the tensile cracks are resulted from the chipping process and the shear cracks are induced by the crushing force with the orientation angle ranging from 45 to 55, which is in good agreement with macro-observations. In Part two, the fragmentation efficiency and penetration rate under different cases are analyzed with several parameters such as the wedge angle, the confinement stress and the penetration velocity. Meanwhile, the blunt indenter is taken as a special case for analysis and comparison of the fragmentation mechanism. (C) 2015 Elsevier Ltd. All rights reserved.

关键词： TBM indentation Wedge indenter Fragmentation Grain-based rock particle flow code

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A hybrid discrete/finite element modeling study of complex hydraulic fracture development for enhanced geothermal systems (EGS) in granitic basements

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GEOTHERMICS 2016年 64卷 362-381页

作者： Hofmann, Hannes Babadagli, Tayfun Yoon, Jeoung Seok Bloecher, Guido Zimmermann, Guenter Univ Alberta Edmonton AB Canada Helmholtz Ctr Potsdam GFZ German Res Ctr Geosci Potsdam Germany

The technical and economic success of enhanced geothermal systems (EGS) in granitic basement rocks depends on the ability to effectively develop complex fracture networks by hydraulic stimulation treatments. To study hydraulic fracture growth horizontally, two dimensional discrete element models were set up for the conditions expected in Precambrian basement rocks in Northern Alberta. The simulated fracture networks were then transferred to a finite element reservoir model to investigate the thermal and hydraulic efficiencies of the fracture networks. Natural and engineering factors influencing stimulated fracture network complexity are summarized and their significance is discussed based on the simulation results. The numerical results fit reasonably well to major field observations and ledto a proposed reservoir stimulation guideline. This guideline involves drilling wells with a horizontal segment at reservoir depth, performing multiple sequential stimulation treatments alternating between two wells with an offset between the stages in both wells, and a long continuous injection of low viscosity fluid at a high rate without proppants. Favorable drilling targets for the development of complex fracture networks are brittle rocks in complex tectonic settings that are characterized by at least two intersecting natural fracture sets that are favorably oriented to the in-situ stress field, a low difference between the major principal stresses, and a low reservoir permeability. The reservoir simulations show the benefit of developing well connected complex fracture networks compared to single parallel hydraulic fractures. (C) 2016 Elsevier Ltd. All rights reserved.

关键词： Interface between DEM and FEM particle flow code OpenGeoSys Hydraulic fracturing design Enhanced geothermal systems Multi-branched fracture development in granites

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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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Numerical analysis on scale effect of elasticity, strength and failure patterns of jointed rock masses

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GEOSCIENCES JOURNAL 2016年第4期20卷 539-549页

作者： Wang, Peitao Yang, Tianhong Xu, Tao Cai, Meifeng Li, Changhong Univ Sci & Technol Beijing Sch Civil & Environm Engn Beijing 100083 Peoples R China Univ Sci & Technol Beijing Key Lab High Efficient Min & Safety Met Mines Minist Educ China Beijing 100083 Peoples R China Northeastern Univ Sch Resources & Civil Engn Shenyang 110819 Peoples R China

It is of great importance to study the failure process and scale effect of jointed rock mass in the field of rock mechanics and mining engineering. In the present paper, initially the uniaxial compression test on granite was performed and acoustic emission (AE) sequence was acquired during the compression process in laboratory. Results from numerical simulations using the particle flow code in two dimensions (PFC2D) were presented, and compared with experimental measurements. It was observed that the approach was reasonably good in predicting the real response of granite rock samples. The mechanical parameter of joint model was then calibrated based on PFC2D model with experimental results. Finally the mechanical properties of complex rocks with discrete fracture network (DFN) were studied and scale effects on the elasticity and strength were then investigated. The result showed that the failure pattern was similar when the ratio of joint contact bond strength (both shear and normal) to rock contact bond strength was in the range of 3 similar to 9%. The elastic modulus and strength parameters were changed with the sizes of rock sample for DFN models. Moreover, the variation of rock failure pattern under different sizes was also studied and finally the representative elementary volume (REV) size of the considered rock mass was estimated to be 9 x 9 m. It is suggested that the failure pattern analysis should be considered in the REV study of jointed rock mass.

关键词： jointed rock mass scale effect representative elementary volume failure pattern particle flow code

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