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Discrete element simulation of crushable rockfill materials

Water Science and Engineering 2013年第2期6卷 215-229页

作者： Lei SHAO Shi-chun CHI Liang-jing ZHOU Yu-zan WANG Faculty of Infrastructure Engineering Dalian University of Technology Hydrochina Chengdu Engineering Corporation Changjiang Institute of Survey Planning Design and Research Changjiang Water Resources Commission

A discrete element method was used to study the evolution of particle crushing in a rockfill sample subjected to triaxial shear. A simple procedure was developed to generate clusters with arbitrary shapes, which resembled real rockfill particles. A theoretical method was developed to define the failure criterion for an individual particle subjected to an arbitrary set of contact forces. Then, a series of numerical tests of large-scale drained triaxial tests were conducted to simulate the behaviors of the rockfill sample. Finally, we examined the development of micro-characteristics such as particle crushing, contact characteristics, porosity, deformation, movement, and energy dissipation. The simulation results were partially compared with the laboratory experiments, and good agreement was achieved, demonstrating that the particle crushing model proposed can be used to simulate the drained triaxial test ofrockfill materials. Based on a comparison of macro behaviors of the roekfill sample and micro structures of the particles, the microscopic mechanism of the rockfill materials subjected to triaxial shear was determined qualitatively. It is shown that the crushing rate, rather than the number of crushed particles, can be used to reflect the relationship between macro- and micro-mechanical characteristics of rockfill materials. These research results further develop our understanding of the deformation mechanism of rockfill materials.

关键词： discrete element simulation triaxial shear test,＂ roclcfill material geometric construction of particles particle flow code microscopic mechanism

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Micro-Study of Soil's Inherent Anisotropy with PFC Simulation

Micro-Study of Soil's Inherent Anisotropy with PFC Simulatio...

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International Conference on Applied Mechanics and Materials (ICAMM 2012)

作者： Li Fan Zhang Kunyong Luo Xingjun Hefei Univ Technol Sch Civil Engn Hefei 230009 Peoples R China Minist Educ Geomech & Embankment Engn Key Lab Nanjing Jiangsu Peoples R China Hohai Univ Inst Geotech Engn Nanjing 210098 Jiangsu Peoples R China

ISBN: (纸本)9783037855911

Based on 2-D PFC, non-circular particle with direction was constructed and specimens with different distribution of long axis orientation were established. Loads were applied in vertical direction. Changes of fabric such as the long axis orientation, particle contact direction and particle contact force in the process of loading were analyzed. It was shown that the larger angle of the loading direction and the long axis orientation, the greater strength of specimen and more anisotropic. It was proved by the numerical analysis that tendency of particle contact stress direction is the micro mechanics reasons of soil's anisotropy under loading.

关键词： particle flow code inherent anisotropy micro-mechanics fabric numerical simulation

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The biaxial compression mechanical properties of crushed rock

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Research in Cold and Arid Regions 2013年第4期5卷 433-439页

作者： PengCheng Wang JianKun Liu Li Liu School of Civil Engineering of Beijing Jiaotong University

Crushed rock subgrade, as one of the roadbed-cooling methods, has been widely used in the Qinghai-Tibet Railway. Much attention has been paid on the cooling effect of crushed rock; however, the mechanical properties of crushed rock are somehow neglected. Based on the discrete element method, biaxial compression test condition for crushed rock is com- piled in FISH language in PFC2D, and the natural shape of crushed rock is simulated with super particle ＂cluster＂. The ef- fect of particle size, crushed rock strength and confining pressure level on overall mechanical properties of the crushed rock aggregate are respectively analyzed. Results show that crushed rock of large particle size plays an essential frame- work role, which is mainly responsible for the deformation of crushed rock aggregate. The strength of gravel has a great influence on overall mechanical properties which means that strength attenuation caused by the freeze thaw cycles cannot be ignored. The stress-strain curves can be divided into two stages including shear contraction and shear expansion at different confining pressures.

关键词： crushed rock subgrade discrete element method particle flow code mechanical property biaxial compression

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Discrete Element Modeling of the Resilient Behavior of Subgrade Sandy Soils

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Procedia - Social and Behavioral Sciences 2013年 96卷 490-495页

作者： Xiao Zhang Key Laboratory of Road and Traffic Engineering of the Ministry of Education Tongji University Shanghai 201804 China Key Laboratory of Highway Construction and Maintenance Technique in Loess Area Shanxi Transportation Research Institute Taiyuan 030006 China

Subgrade soils are very important materials to support highways. Current AASHTO pavement design procedures recommend the resilient modulus (Mr) of subgrade soils or pavement design and analysis. Laboratory repeated triaxial loading tests and field falling weight deflectometer (FWD) are two common ways to characterize the resilient modulus (Mr) of subgrade soils. The primary objective of this study is to conduct numerical simulations of the resilient behavior of subgrade sandy soils under repeated triaxial loading conditions using a commercial discrete elements code, e.g., particle flow code in two dimensions (PFC2D). Stress-controlled loading scheme is designed using a commercial DEM code, particle flow code (PFC2D). One run with a confining stress of 41.4 kPa and deviator stress of 12.4 kPa is conducted for simulating the biaxial test of sandy soils under cyclic loading. Simulation results show that confining stress can be effectively applied to the testing sample. However, the error of axial stress is quite large. In addition, preliminary results of resilient behavior of sandy soils under cyclic loading are consistent with the classic results in real laboratories.

关键词： Subgrade sandy soils resilient modulus (Mr) discrete element method particle flow code repeated triaxial loading tests

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Stress-strain analysis of loess triaxial shear test by PFC^(3D)

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Global Geology 2013年第4期16卷 217-220页

作者： ZHAO Shuyun LI Shibo College of Construction Engineering Jilin University

In order to compensate for limitations of microscopic study on loess triaxial tests, taking the loess in Longxi area as an example, the authors established the loess triaxial test model by using PFC3D software and simulating tfiaxial shear test under the different confining pressures in 0 kPa, 50 kPa and 300 kPa. Compared with laboratory triaxial shear test, the numerical simulation test has a guiding role in loess mechanical strength analysis.

关键词： loess triaxial tests particle flow code stress-strain curve

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Simulation of the sliding process of Donghekou landslide triggered by the Wenchuan earthquake using a distinct element method

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ENVIRONMENTAL EARTH SCIENCES 2012年第4期65卷 1049-1054页

作者： Li, Xinpo He, Siming Luo, Yu Wu, Yong Chinese Acad Sci Inst Mt Hazards & Environm Chengdu 610041 Peoples R China Chinese Acad Sci Key Lab Mt Hazards & Surface Proc Chengdu 610041 Peoples R China

In the village of Donghekou (in Qingchuan County, Sichuan Province, China), a major landslide was triggered by the Wenchuan earthquake in 2008 with more than 10 x 10(6) m(3) of rock displaced. The kinematic behavior of this landslide is simulated using a 2D discrete element model. The numerical model used in this work is composed of discs bonded together. The initial boundary conditions are applied along the ball-wall contacts by using an initial velocity estimated from the strong motion data. The constraints are mainly issued from the final geometry of the landslide including its capacity to dam the river. The modeling thus indicates that a low friction coefficient (about 0.1) is required to account for the actual landslide characteristics. The runout behaviors are analyzed and some useful conclusions are drawn.

关键词： Rock slopes Numerical modeling particle flow code Failure behavior

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A Study of the Failure Mechanism of Planar Non-Persistent Open Joints Using PFC2D

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ROCK MECHANICS AND ROCK ENGINEERING 2012年第5期45卷 677-693页

作者： Ghazvinian, A. Sarfarazi, V. Schubert, W. Blumel, M. Tarbiat Modares Univ Rock Mech Div Tehran Iran Graz Univ Technol Inst Rock Mech & Tunnelling A-8010 Graz Austria

particle flow code 2D (PFC2D) was adopted to simulate the shear behavior of rocklike material samples containing planar non-persistent joints. Direct shear loading was conducted to investigate the effect of joint separation on the failure behavior of rock bridges. Initially calibration of PFC was undertaken with respect to the data obtained from experimental laboratory tests to ensure the conformity of the simulated numerical models response. Furthermore, validation of the simulated models were cross checked with the results of direct shear tests performed on non-persistent jointed physical models. Through numerical direct shear tests, the failure process was visually observed, and the failure patterns were found reasonably similar to the experimentally observed trends. The discrete element simulations demonstrated that the macro-scale shear zone resulted from the progressive failure of the tension-induced micro-cracks. The failure pattern was mostly influenced by joint separation, while the shear strength was linked to the failure pattern and failure mechanism. Furthermore, it was observed that the failure zone is relatively narrow and has a symmetrical pattern when rock bridges occupy a low percentage of the total shear surface. This may be due to the high stress interactions between the subsequent joints separated by a rock bridge. In contrast, when rock bridges are occupying sufficient area prohibiting the stress interactions to occur then the rupture of surface is more complex and turns into a shear zone. This zone was observed to be relatively thick with an unsymmetrical pattern. The shear strength of rock bridges is reduced by increasing the joint length as a result of increasing both the stress concentration at tip of the joints and the stress interaction between the joints.

关键词： particle flow code Non-persistent joint Rock bridge Joint separation Shear and tensile cracks

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An elasto-plastic constitutive model incorporating strain softening and dilatancy for interface thin-layer element and its verification

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Journal of Central South University 2012年第7期19卷 1988-1998页

作者：彭凯朱俊高冯树荣王荣刘汉龙 Hydrochina Zhongnan Engineering Corporation Key Laboratory of Geo-mechanics and Embankment Engineering of Ministry of Education(Hohai University) Geotechnical Research Institute Hohai University

The mechanical behaviors of the interface between coarse-grained soil and concrete were investigated by simple shear tests under condition of mixed soil slurry (bentonite mixed with cement grout).For comparison,the interfaces both without slurry and with bentonite slurry were *** experimental results show that different slurries exert much influence on the strength and deformation of soil/structure *** mixed soil slurry,strain softening and shear dilatation are observed,while shear dilatation appears under the small normal stress of the interface without slurry,and shear contraction is significant under the condition of the bentonite *** thickness of the interface was determined by analyzing the disturbed height of the sample with both simple shear test and particle flow code (PFC).An elasto-plastic constitutive model incorporating strain softening and dilatancy for thin layer element of interface was formulated in the framework of generalized potential *** relation curves of shear stress and shear strain,as well as the relation curves of normal strain and shear strain,were fitted by a piecewise function composed by hyperbolic functions and resembling normal *** entire model parameters can be identified by *** new model is verified by comparing the measured data of indoor cut-off wall model tests with the predictions from finite element method (FEM).The FEM results indicate that the stress of wall calculated by using Goodman element is too large,and the maximum deviation between the test data and prediction is about 45%.While the prediction from the proposed model is close to the measured data,and the error is generally less than 10%.

关键词： simple shear test mixed soil slurry dilatancy particle flow code generalized potential theory constitutive model FEM

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Contact force distribution and induced anisotropy in granular materials under biaxial test

Contact force distribution and induced anisotropy in granula...

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2nd International Conference on Structures and Building Materials (ICSBM)

作者： Hu, Minyun Chen, Qianhao Shen, Ying Tang, Xiaowu Zhejiang Univ Technol Coll Civil Engn & Architecture Hangzhou 310014 Zhejiang Peoples R China Zhongtian Construct Grp CO LTD Hangzhou 310008 Peoples R China Zhejiang Univ Dept Civil Engn Hangzhou 310058 Zhejiang Peoples R China

ISBN: (纸本)9783037853474;9783038137900

A 2-dimensional granular assembly, subjected to isotropic consolidation and biaxial compression, is simulated by applying discrete element method and the particle flow code of PFC2D. The contact force network and distribution are examined and compared to an analogous photoelastic experiment carried out by other studies. The current study shows that the assembly undergoes dilatation and strain-softening after peak strength, and the coordination number (average contact number of particles) increases a little in the initial stage of strain hardening followed by a sharp dropping before the onset of softening. This is correlated with the contact force chain establishment and the evolution of structural anisotropy. The distribution of the normal force and the ratio of tangential to normal force for both the isotropically compressed and sheared stages indicates that the strong normal contacts are crucial for the force chain transmitting stress through assembly. The angular distribution of the contact forces supported this point and could help visualizing the induced anisotropy. These issues are vital for gaining a deeper understanding of the macroscopic behavior of granular material from microscopic analysis.

关键词： particle flow code contact force induced anisotropy biaxial test

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PFC/FLAC Coupled Numerical Simulation of Excavation Damage Zone in Deep Schist Tunnel

PFC/FLAC Coupled Numerical Simulation of Excavation Damage Z...

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2012 3rd International Conference on Information Technology for Manufacturing Systems(ITMS 2012)

作者： Song Wei Hong Ren School of Construction Management and Real Estate Chongqing University

In the present study, a coupled numerical method is used to study EDZ(excavation damage zone) in a deep schist *** codes, Fast Lagrangian Analysis of Continua(FLAC) and particle flow code(PFC) are coupled to implement the *** motive to apply the FLAC/PFC coupled approach is to take advantage of each modeling scheme while at the same time minimizing the requirement for computational *** coupling is realized through an exchange of displacements, velocities, and forces in each cycling *** results are found to be in good agreement with in site ultrasonic wave measured EDZ *** coupled PFC/FLAC model present more information than each uncoupled model individually, and these simulation results are very important in tunnel design.

关键词： Coupling model Numerical simulation particle flow code Fast Lagrangian Analysis of Continua

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