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3D particle-Based DEM Investigation into the Shear Behaviour of Incipient Rock Joints with Various Geometries of Rock Bridges

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ROCK MECHANICS AND ROCK ENGINEERING 2018年第11期51卷 3563-3584页

作者： Shang, J. Zhao, Z. Hu, J. Handley, K. Nanyang Technol Univ Sch Civil & Environm Engn Nanyang Ctr Underground Space Singapore Singapore Cent S Univ Sch Resources & Safety Engn Changsha 410083 Hunan Peoples R China Univ Leeds Sch Earth & Environm Leeds W Yorkshire England

A 3D particle-based DEM model was established taking into account the geometries of rock bridges. The model was used to investigate the shear behaviour of incipient rock joints. Fifty-seven direct shear tests were conducted under constant normal load (CNL) boundary conditions using the established model, in which rock bridges with 19 different geometries and incipient joints with various areal persistence (between 0.2 and 0.96) were involved. Our results show that, for the cases having a single rock bridge, cracks often initiated around the edges of the rock bridges and coalesced first in the middle of the rock bridge areas. While for other cases containing multiple rock bridges, cracks initially appeared at the connection points (located in the middle of the joint planes) of the rock bridges and then propagated to the edges. High crack initiation stresses were measured, which were often more than 60% of the shear strength of the tested incipient rock joints. Sudden failures of the rock bridges subjected to shearing were observed, accompanying dramatic increases in the number of cracks. Another important conclusion derived from this research is that both joint areal persistence and rock bridge geometry played significant roles in the shear failure of the simulated Horton Formation Siltstone joints. The present study has shown that shear strength increased gradually when joint areal persistence was decreased. Interestingly, different shear strength values were measured for rock joints with the same areal persistence (e.g. K=0.5). Shear velocity was also found to have a significant influence on the shear characteristics of the Horton Formation Siltstone joints. A higher shear strength was measured when the shearing velocity was increased from 0.01 to 1m/s.

关键词： Discrete Element Method particle flow code Incipient rock joints Rock bridges Shear strength Joint persistence

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Influence of layered joints on zonal disintegration in deep rock masses under coupled high in-situ axial stress and blasting load

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JOURNAL OF THE SOUTHERN AFRICAN INSTITUTE OF MINING AND METALLURGY 2019年第12期119卷 1019-1026页

作者： Yuan, P. Xu, Y. Anhui Univ Sci & Technol Sch Civil Engn & Architecture Huainan Anhui Peoples R China Anhui Univ Sci & Technol State Key Lab Min Response & Disaster Prevent & C Huainan Anhui Peoples R China Anhui Univ Sci & Technol Engn Res Ctr Underground Mine Construct Minist Educ Huainan Anhui Peoples R China

Zonal disintegration is a characteristic failure mode of deep rock masses under coupled high in-situ axial stress and blasting load. PFC3D numerical simulations were carried out to investigate the influence of inclination angle of widely spaced, layered joints on zonal disintegration. The results indicate that after the four-step blasting procedure, nearly circular contact force chains, which are approximately concentric with the surface of the tunnel, are formed in both intact rock masses and rock masses with layered joints. The number of tension cracks is much greater than that of shear cracks;hence, tension failure predominates as the failure mode for zonal disintegration. Corresponding to the four-step blasting, a time-dependent characteristic is apparent for crack propagation and released strain energy evolution during the advance of the tunnel. Zonal disintegration can be intensified by extending the duration of the blasting load, and alleviated by extending the blasting rise time. The inclination angle of layered joints has a significant effect on zonal disintegration. With an increase of inclination angle, both the number of cracks and released strain energy first increase and then decrease, which is consistent with the distribution of contact force chains. When the inclination angle of layered joints is 60 degrees, the joints present a strong influence on intensifying the zonal disintegration.

关键词： zonal disintegration layered joints inclination angle particle flow code contact force chain

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A particle-based numerical investigation on longwall top coal caving mining

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ARABIAN JOURNAL OF GEOSCIENCES 2019年第18期12卷 556-556页

作者： Song, Zhengyang Konietzky, Heinz TU Bergakad Freiberg Geotech Inst Gustav Zeuner Str 1 D-09599 Freiberg Germany

A 3D particle-based numerical approach to simulate the longwall top coal caving (LTCC) process was proposed, which for the first time the effect of continuous support advance and the face-end support were considered. The shape of drawing body and top coal boundary and the distribution characteristics of coal loss were analysed. The top coal flow trajectories and velocity fields were visualized and consistent with the assumptions in Bergmark-Roos model. The vertical forces on the drawing support beams were continuously monitored during the process of simulation. It was found that both the drawing procedure and the support advance will lead to a reduction of the vertical forces on support beams. Results of the numerical simulations and laboratory testing were compared and good consistency was obtained.

关键词： Coal particle flow code Longwall top coal caving (LTCC) Numerical simulation Bergmark-Roos model

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Analysis of Rock Damage Characteristics Based on particle Discrete Element Model

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GEOTECHNICAL AND GEOLOGICAL ENGINEERING 2018年第2期36卷 897-904页

作者： Zhao, Zhen-long Wang, Xiao Wen, Zhi-jie Shandong Univ Sci & Technol State Key Lab Min Disaster Prevent & Control Shandong Prov & Minist Sci & Technol Qingdao 266590 Peoples R China Southeast Univ Sch Civil Engn Nanjing 210096 Jiangsu Peoples R China

Rock is a heterogeneous medium that is composed of minerals of various sizes. Under the action of external loads, the generation, propagation and coalescence of microdefects in the rock mass determines the macroscopic deformation and fracture of rock. To understand the damage law of rock and to reveal the evolution of dynamic failure, a uniaxial compression model was established based on particle flow code. Acoustic emission and energy characteristics of rock damage were analyzed, and the damage constitutive models of rock were discussed. During rock uniaxial compression, acoustic-emission events undergo a relatively quiet, sudden increase and sharp decrease for three periods, which corresponds to the compaction and elastic deformation stage, yield stage and post-peak stage in the stress-strain curve. Before the yield stress is reached, the proportion of bond and strain energies is larger. Friction energy accounts for a small proportion of the total energy, and a reciprocal relationship exists between them. The constitutive model that is based on friction energy can better reflect the variation in stress and strain, then the constitutive model based on acoustic-emission parameters.

关键词： Rock mass Damage evolution Acoustic emission Energy Constitutive model particle flow code

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Analysis of the deformation and fracture of underground mine roadway by joint rock mass numerical model

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ARABIAN JOURNAL OF GEOSCIENCES 2019年第18期12卷 559-559页

作者： Jin, Aibing Wang, Benxin Zhao, Yiqing Wang, He Feng, He Sun, Hao Yang, Zhenwei Univ Sci & Technol Beijing Minist Educ Key Lab High Efficiency Min & Safety Met Mines Beijing 100083 Peoples R China Univ Sci & Technol Beijing Sch Civil & Resources Engn Beijing 100083 Peoples R China Beijing Gen Res Inst Min & Met Technol Grp Beijing 102628 Peoples R China China Railway Fifth Survey & Design Inst Grp Beijing 102600 Peoples R China

Joints in the rock mass and rheological properties are the main contributing factors in many engineering disasters. Using the user-defined visco-elastoplastic Nishihara constitutive model based on particle flow code in three dimensions (PFC3D), a jointed rock mass numerical model was built to analyze rheological properties and failure behavior of a tunnel surrounded by jointed rock mass of the Zhangjiawa iron mine, Shandong Province, China. The joint distribution law was determined from a statistical analysis of joints on the tunnel walls. Based on the tunnel joint network constructed by the Monte-Carlo method, a jointed rock mass numerical model was established. The rheological properties of the jointed rock mass were separately analyzed by the Nishihara model and the linear elastic model. According to the result from the linear elastic model, the deformation of the tunnel roof and sides did not change with time and the model did not exhibit rheological properties. In contrast, the result of the user-defined Nishihara model showed obvious creep property. The bonds of the joint faces in the jointed rock mass model were primarily destroyed by shear failure. The failure modes and deformation data for the tunnel were generally consistent with field monitoring data.

关键词： particle flow code Nishihara model Jointed rock mass numerical model Rheological properties Roadway deformation and fracture

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Influence of Grain Size Heterogeneity and In-Situ Stress on the Hydraulic Fracturing Process by PFC^2D Modeling

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ENERGIES 2018年第6期11卷

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

A modified fluid-mechanically coupled algorithm in PFC2D was adopted in this article to study the influence of grain size heterogeneity and in-situ stress on hydraulic fracturing behavior. Simulated results showed that the in-situ stress and grain size heterogeneity significantly affect the initiation, growth, and spatial distribution of the hydraulic fractures: (1) the initiation and breakdown pressure are gradually reduced with the increase of the grain size heterogeneity;(2) with increased in-situ stress, the initiation and breakdown pressure increase, and the reduction effect of grain size heterogeneity on the breakdown pressure becomes more obvious;(3) in grain size homogeneous rock, the initiation pressure decreases with increasing in-situ stress ratio, however, the initiation pressure of grain size heterogeneous rock is almost unaffected by the in-situ stress ratio;(4) The in-situ stress ratio and grain size heterogeneity affect the spatial distribution of hydraulic fractures simultaneously. When the in-situ stress ratio is larger than 1, the hydraulic fractures propagate substantially along the direction of the maximum principal stress. When the in-situ stress ratio is 1, the initiation position and extension direction of hydraulic fractures are random and complex fracture networks can easily develop in a grain size homogeneous model.

关键词： hydraulic fracturing grain size heterogeneity in-situ stress particle flow code modified fluid-mechanically coupled model

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Height of the mining-induced fractured zone above a coal face

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ENGINEERING GEOLOGY 2017年 216卷 140-152页

作者： Wang, Gang Wu, Mengmeng Wang, Rui Xu, Hao Song, Xiang Shandong Univ Sci & Technol Mine Disaster Prevent & Control Minist State Key Lab Breeding Base Qingdao 266590 Peoples R China Shandong Univ Sci & Technol Coll Min & Safety Engn Room 108579 Qianwangang Rd Qingdao 266590 Peoples R China

The development height of a gas conducting fracture zone (GFZ) in the gob overlying strata is crucial to the gas drainage and safe production of a coal mine. In order to address the issues of excessive gas concentration and uncertain GFZ height in No. 7435 Face overlying strata of Kongzhuang Coal Mine, China, the caving characteristics of overlying strata were explored using both physical experiments on similar materials and numerical simulations of particle flow code (PFC) software and verified each other. The relationship of cracks development to porosity changing characteristics was introduced to quantitatively determine the height of the local GFZ. The quantified GFZ heights were compared with those measured using the in-situ drilling flow method. The results showed that 1) PFC software could accurately simulate the overlying strata caving behaviors, thus saving manpower, materials and financial resources needed for related physical experiments, and 2) the temporospatial distribution characteristics of porosity could be used to forecast GFZ height, and are of significant importance for determination of GFZ. Overall, the conclusions are of engineering significance for accurate arrangement of boreholes for gas drainage and reduction of mine gas disasters. (C) 2016 Elsevier B.V. All rights reserved.

关键词： Fracture zone Empirical formula Similar material model particle flow code Key stratum Site observation

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Mechanical behavior and failure mechanism of pre-cracked specimen under uniaxial compression

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TECTONOPHYSICS 2017年 712卷 330-343页

作者： Liu, Ting Lin, Baiquan Yang, Wei China Univ Min & Technol Minist Educ Key Lab Coal Methane & Fire Control Xuzhou 221116 Peoples R China China Univ Min & Technol Sch Safety Engn Xuzhou 221116 Peoples R China

As a desirable permeability enhancement method, hydraulic slotting has been widely used for enhanced coal bed methane (ECBM) recovery in China. Aiming at the problem that the action mechanism of the slot on the mechanical properties of the slotted coal is still unclear, this paper investigates the effects of flaw inclination on the strength, deformation and cracking process of the pre-cracked specimens. The result shows that the stress-strain curves can be divided into three categories based on the stress behaviors, dropping step by step or dropping sharply, after the peak. With an increase of the flaw inclination, the strength and elastic modulus of the pre-cracked specimen increases gradually, which is verified by the numerical simulation and theoretical results. Analysis of the cracking processes indicates that the initiation position of the first crack in specimens with various flaw inclinations is different, which is caused by the various distributions of tensile and compressive stress concentration zones. The distribution of the stress field controls the cracking process which will in turn affect the stress field distribution. With the propagation of the cracks, the tensile stress concentration zones expand and the concentration degree lowers gradually, while the compressive stress concentration zones show the opposite variation trend. Based on the above results, an optimized slot arrangement method has been proposed for the field application of hydraulic slotting. (C) 2017 Elsevier B.V. All rights reserved.

关键词： Pre-cracked specimen Failure mechanism Acoustic emission Stress field particle flow code

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

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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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Effects of Microparameters on Macroparameters of Flat-Jointed Bonded-particle Materials and Suggestions on Trial-and-Error Method

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GEOTECHNICAL AND GEOLOGICAL ENGINEERING 2017年第2期35卷 663-677页

作者： Chen, Peng-yu Neijiang Normal Univ Sch Geog & Resource Sci Neijiang 641100 Sichuan Peoples R China

The aims of this paper are to analyze the effects of microparameters on macroparameters of flat-jointed bonded-particle materials of particle flow code in two dimensions (PFC2D) and improve the efficiency of trial-and-error method in calibration of microparameters. The trial-and-error method is always used to calibrate the microparameters for a PFC2D model, but it is time-consuming and empirical. To improve the efficiency of the trial-and-error method, the effects of microparameters on macroparameters need to be analyzed. By using the trial-and-error method, a desirable set of microparameters for a uniaxial compression PFC2D model (with a flat-joint contact model as the contact model) of limestone were calibrated to match the macroscopic properties obtained from laboratory tests. Based on the calibration set of microparameters, effects of microparameters on macroparameters of the PFC2D model were studied by the orthogonal design method. On this basis, a flowchart of calibrating microparameters via trial-and-error method was proposed. This flowchart was used to calibrate the microparameters of granite. The macroparameters and failure characteristics determined from numerical simulation were very similar to those of laboratory tests, confirming the effectiveness of the proposed flowchart.

关键词： particle flow code Flat-joint contact model Rock Macroparameters Microparameters Trial-and-error method

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