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Modelling the shearing behaviour of joints using an improved shear box genesis approach in particle flow code (2D) and its validation

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GEOMECHANICS AND GEOPHYSICS FOR GEO-ENERGY AND GEO-RESOURCES 2020年第1期6卷 1-15页

作者： Li, H. Deng, J. H. Yin, J. H. Zhu, J. B. Sichuan Univ Sichuan Univ Hong Kong Polytech Univ Inst Disaste Chengdu Peoples R China Sichuan Univ State Key Lab Hydraul & Mt River Engn Chengdu Peoples R China Hong Kong Polytech Univ Dept Civil & Environm Engn Hong Kong Peoples R China Tianjin Univ Sch Civil Engn State Key Lab Hydraul Engn Simulat & Safety Tianjin Peoples R China

The smooth joint contact model has been used extensively to simulate the shear behaviour of joints in the numerical simulations with particle flow code. Results from existing studies have revealed that this model suffers from the particle interlocking problem taking place at the shear displacement greater than the minimum particle diameter. To solve this problem, the shear box genesis approach was proposed, by which particles in the upper and lower halves of a joint are generated separately, and the intended joint plane will be added as a common boundary. However, the shear box genesis approach is not a satisfactory solution to the interlocking problem yet. Three problems are usually encountered in practice: first, particles are still likely to move across the intended joint plane and cause the interlocking;second, the shear box genesis approach inevitably causes the periodic change in the contact number along the intended joint plane;third, it is difficult to incorporate the nonlinear closure behaviour of joints. Therefore, this paper aims to solve the shortcomings, and to apply the improvements to the simulation of joint shear behaviour. The interlocking problem was successfully solved by introducing the joint side checking method, and specifying the value of maximum allowed closure. The periodic stress fluctuation during shearing was eliminated by the non-unified ball generation method. The nonlinear closure behaviour of joints was captured by embedding the Barton-Bandis model. To verify the applicability of the improvements to rough joints, a series of numerical and experimental direct shear tests of rough joints were conducted. In general, good agreements were achieved between the numerical modelling results and laboratory measurements. This improved shear box genesis approach enhances the ability of the smooth joint contact model to simulate the shear behaviour of joints, and also has the ability to track the damage evolution during the joint shearing process.

关键词： Rock joint particle flow code Shear box genesis method Direct shear test

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Numerical simulation of column charge explosive in rock masses with particle flow code

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GRANULAR MATTER 2019年第4期21卷 1-17页

作者： Yang, Junxiong Shi, Chong Yang, Wenkun Chen, Xiao Zhang, Yiping Hohai Univ Key Lab Minist Educ Geomech & Embankment Engn Nanjing 210098 Jiangsu Peoples R China Hohai Univ Res Inst Geotech Engn Nanjing 210098 Jiangsu Peoples R China

The detonation of a column charge and the damage process in a rock mass are simulated in this study by the particle flow code method. The expansion loading method and the dynamic boundary treatment method are established according to the discrete element mechanism. Mechanical parameters are calibrated on the basis of the Starfield superposition principle and the dynamic compensation method. Dynamic stiffness and microscopic parameters are used for numerical simulations. Numerical test results are consistent with lab experimental test results. The velocity attenuation law is compared with that of theoretical results, and the blasting crater action index is compared with that of field test results, to verify the rationality of the numerical explosion model of the column charge. The mechanism of the rock breaking process under column charge explosion is analyzed. Stress wave propagation, detonation wave propagation, and crack extension are investigated. The stress wave gradient law is obtained, and the effects of blasting rock breaking, crack extension, and explosion effect outside the blasting crater area are determined with different initiation modes. The research method can explain the blasting stress wave propagation law and describe the dynamical failure process in rock masses. This study can provide a reliable numerical analysis method for follow-up blasting research and offer practical guidance on engineering blasting.

关键词： particle flow code Explosive stress wave Blasting crater Crack Detonation

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Numerical Study of Damage Evolution Law of Coal Mine Roadway by particle flow code (PFC) Model

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GEOTECHNICAL AND GEOLOGICAL ENGINEERING 2019年第4期37卷 2883-2891页

作者： Liu, Wan-rong Wang, Xiao Li, Chuan-ming Anhui Univ Sci & Technol Minist Educ Key Lab Safety & High Efficiency Coal Min Huainan 232001 Peoples R China Liaocheng Univ Sch Phys Sci & Informat Engn Liaocheng 252059 Shandong Peoples R China Southeast Univ Sch Civil Engn Nanjing 210096 Jiangsu Peoples R China

Deformation and destruction of roadway surrounding rock is one of the main causes of coal mine accidents. In this paper, the horseshoe-shaped roadway model was established by particle flow code firstly and then analyzed the roadway damage process through the contact force chain, deformation displacement and distribution of micro-cracks. The research result show that the parallel bond model can well simulate the damage process of the coal mine roadway. The surrounding rock can be divided into four zones from the roadway side to the deep rock mass. The micro-contact force chain is the force transmission path and the principal stress is the macroscopic reflection of the micro-contact force chain.

关键词： Roadway particle flow code Surrounding rock Damage evolution

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An Improved Shear Stress Monitoring Method in Numerical Direct Shear Tests by particle flow code

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JOURNAL OF TESTING AND EVALUATION 2020年第6期48卷 4136-4152页

作者： Jiang, Yaofei Wang, Liangqing Wu, Qiong Sun, Zihao Elmo, Davide Zheng, Luobin China Univ Geosci Fac Engn 388 Lumo Rd Wuhan 430074 Hubei Peoples R China Univ British Columbia NBK Min Dept Vancouver Campus513-6350 Stores Rd Vancouver BC V6T 1Z4 Canada

During a direct shear test in particle flow code (PFC;Itasca Consulting Group, Minneapolis, MN) simulation, the initial force is often neglected by the existing methods of monitoring shear stress, which results in a difference between the monitoring data and simulation result. An improved monitoring method, which involves monitoring the resultant force on the left and right walls (specimen boundary) as the shear force, is proposed to monitor the shear stress in this study. The effectiveness of the proposed method is first investigated by comparing the monitoring results with the peak shear strength of sawtooth triangular joints with base angles of 0 degrees, 15 degrees, and 30 degrees and joints with Barton's standard joint roughness profiles (joint roughness coefficient (JRC) = 5.8, 10.8, and 14.5) as predicted by well-known classical shear models under different normal stress conditions. Additionally, the capabilities of the proposed monitoring method were tested by comparing it with the peak shear strength obtained from laboratory direct shear tests on a real rock joint (JRC = 1.0) under different normal stress levels. Good agreement was found between the results of the numerical models that used the proposed monitoring method and well-known classical shear models as well as laboratory direct shear tests. The proposed method has a highly accurate capacity for determining the shear stress in numerical direct shear tests by PFC. This method has advantages for assessing joints with low roughness coefficients under low normal stress conditions. The results reveal that the proposed method reasonably reflects the shear characteristics of rock joints in numerical direct shear tests. The proposed method also contributes to the calibration of microparameters for a smooth joint model to more accurately represent the rock joint.

关键词： shear stress direct shear test rock joints particle flow code

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Three-Dimensional Reconstruction of Biomineralized Sand and particle-flow-code Numerical Simulation of Penetration Resistance Characteristics of Biomineralization Crust

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INTERNATIONAL JOURNAL OF GEOMECHANICS 2021年第5期21卷

作者： Zhang, Jinbang Li, Chi Wang, Shuo Bai, Siriguleng Inner Mongolia Univ Technol Coll Civil Engn Hohhot 010051 Peoples R China Inner Mongolia Univ Technol Coll Sci Hohhot 010051 Peoples R China

When fine sand is treated with microbial-induced calcite precipitation (MICP), the connections of loose sand particles are reinforced by being filled with crystals of calcium carbonate (CC) caused by the presence of microorganisms. According to the research of scholars, in the process of MICP, the common anhydrous CC crystals are calcite, vaterite, and aragonite. To explore the factors that influence the penetration resistance (PR) of a biomineralization crust (BMC) and to consider the influence of sand particles and CC crystal morphology on strength, this paper reconstructs the sand particles and CC crystals by means of three-dimensional reconstruction from photographic images. Two numerical models based on a particle flow code were established using the discrete element method and were used to investigate separately (1) the unconfined compressive strength (UCS) of a biomineralized sand column;and (2) the PR of a BMC. The research shows that the UCS of an MICP sand column of calcite crystal form is 4.9 MPa, which is 2.39 times that of one of vaterite forms. It is found that the thickness of the BMC and its CaCO3 content has a great influence on the PR of the BMC. The PR shows an increasing trend due to the increase of CC content when the penetration speed is 1.5 m/s and the coating thickness of the coating layer is 2.5 cm. The PR test value at 2.5 cm in the soil layer increases from 52.8 to 103.9 kPa when the penetration speed is 1.5 m/s, the CaCO3 content is 12%, and the thickness of the BMC is increased from 2.5 to 4.5 cm. It is concluded that because the thickness of the BMC and the CC content increases, the PR of the test points in the soil also increases. The results of this study complement the test results of a field-scale experiment and have important value for the large-scale application of MICP technology to desert sites for desertification control.

关键词： Microbial-induced calcite precipitation Three-dimensional reconstruction Calcium carbonate crystals particle flow code Penetration resistance Biomineralization crust

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Mechanical Behavior of Polyurethane Polymer Materials under Triaxial Cyclic Loading:A particle flow code Approach

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Journal of Wuhan University of Technology(Materials Science) 2018年第4期33卷 980-986页

作者：刘恒 WANG Fuming 石明生 TIAN Wenling School of Water Conservancy and Environment Zhengzhou University School of Civil and Transportation Engineering Henan University of Urban Construction State Key Laboratory for Geomechanics and Deep Underground Engineering China University of Mining & TechnologyXuzhou

Polyurethane polymer grouting materials were studied with conventional triaxial tests via the particle flow code in two dimensions（PFC^（2D）） method, and the simulation results agreed with the experimental data. The particle flow code method can simulate the mechanical properties of the polymer. The triaxial cyclic loading tests of the polymer material under different confining pressures were carried out via PFC^（2D） to analyze its mechanical performance. The PFC^（2D） simulation results show that the value of the elastic modulus of the polymer decreases slowly at first and fluctuated within a narrow range near the value of the peak strength; the cumulative plastic strain increases slowly at first and then increases rapidly; the peak strength and elastic modulus of polymer increase with the confining pressure; the PFC^（2D） method can be used to quantitatively evaluate the damage behavior of the polymer material and estimate the fatigue life of the materials under fatigue load based on the number and the location of micro-cracks. Thus, the PFC^（2D） method is an effective tool to study polymers.

关键词： polymer particle flow code cyclic loading elastic modulus micro-cracks axial strain

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Stress Evolution of Rock-Like Specimens Containing a Single Fracture Under Uniaxial Loading: a Numerical Study Based on particle flow code

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GEOTECHNICAL AND GEOLOGICAL ENGINEERING 2018年第1期36卷 567-580页

作者： Liu, Jie Wang, Jun Hunan Inst Engn Dept Bldg Engn Xiangtan Peoples R China Hunan Prov Key Lab Safe Min Tech Coal Mines Xiangtan Peoples R China

Stress concentrations are responsible for the crack propagation in rock and rock-like specimens. To investigate the stress evolution characteristics of the rock-like specimens containing a single prefabricated fracture, a numerical study based on the particle flow code was conducted. The numerical results indicate that the concentrated tensile stress and shear stress are responsible for the wing and secondary crack propagation. At the early compression stage, wing cracks tend to form by the concentrated tensile stress, whereas the secondary crack forms by the shear plane resulting from the shear stress concentration at later compression stage. Additionally, the increase in the inclination angle restrains the wing crack propagation. Moreover, in the propagation process of the typical wing and secondary cracks, sudden decreases of the tensile and shear stresses are observed. These decreases at the former monitor points are always accompanied with the sharp increases at the latter points. Furthermore, the results show that the wing and secondary cracks develop in different manners. The large axial strain gaps between adjacent monitor points for wing crack propagation indicates that the wing crack propagates in a stable and slow way, whereas the significantly reduced gaps indicate that the secondary crack propagates in a speedy and unstable way.

关键词： Stress evolution Rock-like specimen Single fracture particle flow code

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Calibration of micro-scaled mechanical parameters of granite based on a bonded-particle model with 2D particle flow code

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GRANULAR MATTER 2019年第2期21卷 38-38页

作者： Shi, Chong Yang, Wenkun Yang, Junxiong Chen, Xiao Hohai Univ Key Lab Minist Educ Geomech & Embankment Engn Nanjing 210098 Jiangsu Peoples R China Hohai Univ Inst Geotech Res Nanjing 210098 Jiangsu Peoples R China

From a microscopic perspective, the mechanical behavior of rocks can be well simulated by particle discrete element method. However, the ideal mechanical properties under macroscopic compression and tension conditions of the granular system require not only reasonable micro-parameters but also consider the mineral distribution in rock microstructure. In this study, the internal microstructure of granite was characterized based on digital images. The cellular automata method was used to construct a discrete element model of clustered particles, and a rapid and effective calibration method for rock microscopic parameters was established. Numerical results significantly relate with laboratory test results, and the microscopic mechanical parameters of the rock were rapidly predicted. Clustered discrete element model simulated the macroscopic mechanical behavior of the investigated rock by considering microscopic rock structure while ignoring particle shape. Results showed that bond strength ratio of the filler-matrix in the numerical sample can significantly affect the compressive-tensile strength ratio. Further, the internal mineral proportion and degree of mineral contact damage strongly influenced the macroscopic mechanical behavior of the investigated rock. Results of this study can provide basis for the construction of micro-scaled model and calibration of microscopic parameters for investigation of rock mechanical behavior.

关键词： Microscopic structure particle flow code Discrete element method Compressive-tensile strength ratio

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Improvements for the smooth joint contact model of the particle flow code and its applications

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COMPUTERS AND GEOTECHNICS 2017年 87卷 163-177页

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

This paper deals with two shortcomings of the smooth-joint contact model (SJCM) used in the particle flow code (PFC). The first shortcoming is the increase of the shear strength of the joint when the shear displacement of the joint exceeds a specific value that is related to the particle size. This problem is named as the interlocking problem, which is caused by the interlocking particles. It occurs due to a shortcoming of the updating procedure in the PFC software related to the contact conditions of the particles that lie around the intended joint plane during high shear displacements. This problem also increases the dilation angle and creates unwanted fractures around the intended joint plane. To solve this problem two new approaches are proposed in this paper: (1) joint plane checking (JPC) approach and (2) joint sides checking (JSC) approach. These approaches and the regular approach are used to model: (a) the direct shear test using the PFC2D and PFC3D, (b) the biaxial test on a sample having a persistent joint with a dip angle varying from 0 degrees to 90 degrees at an interval of 15 degrees using the PFC2D and (c) the polyaxial test on two samples, one of them having a joint with a dip direction of 0 degrees and the dip angle varying from 0 degrees to 90 degrees at an interval of 15, and the other sample having a joint with a dip angle of 60 degrees and the dip direction varying from 0 degrees to 90 degrees at an interval of 15 degrees using the PFC3D. All numerical results show that the JPC and JSC approaches can solve the interlocking problem. Also, they proved to be more consistent with the theory compared to the regular approach. However, the JPC approach leads to a slightly softer joint. Therefore, the JSC approach is suggested for jointed rock modeling using the PFC. The other shortcoming of the SJCM dealt within this paper is its inability to capture the non-linear behavior of the joint closure varying with the joint normal stress. This problem is sol

关键词： Discrete element method particle flow code jointed rock mass modeling Smooth-joint contact model Anisotropic jointed rock mass behavior Joint normal stiffness

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Effect of normal load on the crack propagation from pre-existing joints using particle flow code (PFC)

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COMPUTERS AND CONCRETE 2017年第1期19卷 99-110页

作者： Haeri, Hadi Sarfarazi, Vahab Zhu, Zheming Islamic Azad Univ Bafgh Branch Young Researchers & Elite Club Bafgh Iran Hamedan Univ Technol Dept Min Engn Hamadan Iran Sichuan Univ Coll Architecture & Environm Chengdu 610065 Peoples R China

In this paper, the effect of normal load on the failure mechanism of echelon joint has been studied using PFC2D. In the first step, calibration of PFC was undertaken with respect to the data obtained from experimental laboratory tests. Then, six different models consisting various echelon joint were prepared and tested under two low and high normal loads. Furthermore, validation of the simulated models were cross checked with the results of direct shear tests performed on non-persistent jointed physical models. The simulations demonstrated that failure patterns were mostly influenced by normal loading, while the shear strength was linked to failure mechanism. When ligament angle is less than 90, the stable crack growth length is increased by increasing the normal loading. In this condition, fish eyes failure pattern occur in rock bridge. With higher ligament angles, the rock bridge was broken under high normal loading. Applying higher normal loading increases the number of fracture sets while dilation angle and mean orientations of fracture sets with respect to ligament direction will be decreased.

关键词： particle flow code rock bridge angle normal load shear and tensile cracks

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