Numerical investigation on permeability evolution behavior of rock by an improved flow-coupling algorithm in particle flow code

Permeability is a vital property of rock mass, which is highly affected by tectonic stress and human engineering activities. A comprehensive monitoring of pore pressure and flow rate distributions inside the rock mass is very important to elucidate the permeability evolution mechanisms, which is difficult to realize in laboratory, but easy to be achieved in numerical simulations. Therefore, the particle flow code （PFC）, a discrete element method, is used to simulate permeability behaviors of rock materials in this study. Owe to the limitation of the existed solid-fluid coupling algorithm in PFC, an improved flow-coupling algorithm is presented to better reflect the preferential flow in rock fractures. The comparative analysis is conducted between original and improved algorithm when simulating rock permeability evolution during triaxial compression, showing that the improved algorithm can better describe the experimental phenomenon. Furthermore, the evolution of pore pressure and flow rate distribution during the flow process are analyzed by using the improved algorithm. It is concluded that during the steady flow process in the fractured specimen, the pore pressure and flow rate both prefer transmitting through the fractures rather than rock matrix. Based on the results, fractures are divided into the following three types： I） fractures link to both the inlet and outlet, II） fractures only link to the inlet, and III） fractures only link to the outlet. The type I fracture is always the preferential propagating path for both the pore pressure and flow rate. For type II fractures, the pore pressure increases and then becomes steady. However, the flow rate increases first and begins to decrease after the flow reaches the stop end of the fracture and finally vanishes. There is no obvious pore pressure or flow rate concentration within type III fractures.

Failure mechanism and stability analysis of the Zhenggang landslide in Yunnan Province of China using 3D particle flow code simulation

Based on the principle of 3D particle flow code,a numerical landslide run-out model is presented to simulate the failure process of the Zhenggang landslide(in southwestern China) under the effect of water after a rainfall.The relationship between the micro-mechanical parameters and the macro-shear strength of the grain material is determined through numerical calibrations.Then the rainfall effect is considered in numerical simulations and rain-induced sliding processes are performed,which help us to discuss the mechanism of deformation and failure of this landslide together with field observations.It shows the Zhenggang landslide would most likely be activated in Zone I and would gain momentum in Zone II.In order to prevent the potential disaster,a tailing dam is advised to be designed about 175 m downstream from the current landslide boundary of Zone II.Verified by field observations,the presented landslide model can reflect the failure mechanism after rainfall.It can also provide a method to predict the potential disaster and draft disaster prevention measures.

Particle flow code simulation of intact and fissured granitic rock samples

This study presents a calibration process of three-dimensional particle flow code(PFC3D)simulation of intact and fissured granite samples.First,laboratory stressestrain response from triaxial testing of intact and fissured granite samples is recalled.Then,PFC3D is introduced,with focus on the bonded particle models(BPM).After that,we present previous studies where intact rock is simulated by means of flatjoint approaches,and how improved accuracy was gained with the help of parametric studies.Then,models of the pre-fissured rock specimens were generated,including modeled fissures in the form of“smooth joint”type contacts.Finally,triaxial testing simulations of 1 t 2 and 2 t 3 jointed rock specimens were performed.Results show that both elastic behavior and the peak strength levels are closely matched,without any additional fine tuning of micro-mechanical parameters.Concerning the postfailure behavior,models reproduce the trends of decreasing dilation with increasing confinement and plasticity.However,the dilation values simulated are larger than those observed in practice.This is attributed to the difficulty in modeling some phenomena of fissured rock behaviors,such as rock piece corner crushing with dust production and interactions between newly formed shear bands or axial splitting cracks with pre-existing joints.

Mechanical Behavior of Polyurethane Polymer Materials under Triaxial Cyclic Loading:A Particle Flow Code Approach

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.

Effect of curing time on the mesoscopic parameters of cemented paste backfill simulated using the particle flow code technique

Several special mechanical properties,such as dilatancy and compressibility,of cemented paste backfill(CPB)are controlled by its internal microstructure and evolution.The mesoscopic structure changes of CPB during the development process were investigated.On the basis of the scanning electron microscopy(SEM)and mechanical test results of CPB,the particle size information of CPB was extracted,and a two-dimensional particle flow code(PFC)model of CPB was established to analyze the evolution rule of mesoscopic parameters during CPB development.The embedded FISH language in PFC was used to develop a program for establishing a PFC model on the basis of the SEM results.The mesoscopic parameters of CPB samples at different curing times,such as coordination number(C_(n)),contact force chain,and rose diagram,were obtained by recording and loading and used to analyze the intrinsic relationship between mesoscopic parameter variations and macroscopic mechanical response during CPB development.It is of considerable significance to establish the physical model of CPB using the PFC to reveal the mesoscopic structure of CPB.

Evaluation of plow system performance in long-wall mining method using particle flow code

The underground or open-pit methods are used for the extraction of mineral resources,each of which is divided into different categories.Coal is one of the mineral resources,which is exploited either by the surface or the underground methods.The long-wall mining is one of the methods for the underground coal mining.In this method,which is a mechanized one,some machines such as the shearer or plow are used for the mining.The coal mine in Parvadeh,Tabas is a mechanized mine that is extracted by the long-wall mining.The modeling with particle flow code software was used in this mine for the evaluation of plow performance using the coal specifications.In this regard,the sample was first calibrated by sampling from the Parvadeh coal mine and performing the uniaxial and Brazilian tests on the model.Then,the modeling was done by constructing the model and using the variables such as the clearance angle and the linear velocity of the plow.After making 28 models for the plow,the best model of the plow was selected based on the maximum force applied to the machine in the X direction.Finally,the results of this study showed that the best plow performance is for a model with the clearance angle of zero and the linear velocity of 9 mm/min,and the maximum force applied to this model is equal to 39,000 kN in the X direction.

PFC软件在建材矿山溜井落矿方面的模拟应用探讨

利用Itasca PFC(Particle Flow Code)软件对建材矿山的矿石溜井放矿过程进行模拟,通过对溜井内矿石运动模拟具体过程的详细分析,总结了矿石在溜井内的运动规律及其对井壁的冲击位置。通过模拟,优化溜井设计,提高溜井使用的安全性,减少对井壁的冲击损伤。并对利用PFC软件进行此类模拟的优势进行了探讨。

含弧形裂隙花岗岩裂纹扩展特征PFC模拟

为了研究非直裂隙对岩石强度及破裂特征的影响,对含弧形裂隙岩样进行单轴压缩模拟,探讨弧形裂隙几何参数对试样宏细观力学行为的影响规律。首先,利用颗粒流程序(PFC)构建花岗岩试样数值模型,通过与完整和含单直裂隙试样室内试验结果进行比较,标定1组能够反映花岗岩力学特性的细观参数。在此基础上,对含不同裂隙倾角α和裂隙长短轴比γ的弧形裂隙试样进行单轴压缩模拟。研究结果表明:1)含弧形裂隙试样的峰值强度和弹性模量随着α增大而增大。当α=0°和45°时,试样的峰值强度和弹性模量随着γ的增大而增大;当α=90°时,试样的峰值强度和弹性模量随着γ的增大而减小。2)含弧形裂隙试样主要发生拉伸破坏,初始裂纹在裂隙尖端萌生,随着α增加,试样的破坏程度逐渐增大;γ主要影响裂纹类型、数量和萌生位置。3)首先在弧形裂隙尖端出现应力集中,初始裂纹产生后在裂纹尖端附近出现应力集中,微裂纹逐渐聚集、连通形成宏观裂纹,宏观裂纹的不断扩展导致试样破坏。

奥陶系灰岩顶部劈裂注浆裂隙起裂机制PFC数值分析

超前区域注浆是煤层底板灰岩水害防治的有效手段,而注浆工程中的劈裂注浆过程是决定注浆效果的关键环节,但由于对受注灰岩地层裂隙起裂机制认识不清,致使劈裂注浆过程中注浆压力、浆液水灰比等参数缺少有效控制,难以保证注浆效果。针对上述问题,利用颗粒元(Particle Flow Code,PFC)数值模拟软件,考虑浆液水灰比、地应力水平、弱面和裂隙的倾角和宽度等因素,开展奥陶系灰岩顶部劈裂注浆数值模拟计算。结果表明:在弱面和裂隙条件下起裂压力均随浆液水灰比(1∶1、2∶1、3∶1)的增大而减小,随最大主应力与最小主应力差值(9、12、15 MPa)的减小而增大,随弱面或裂隙宽度(3、8、15 mm)及其与最大主应力夹角(30°、60°、90°)的增大而减小;起裂裂隙沿平行于最大主应力方向延展;起裂压力值随弱面与基质强度比(0.30、0.03)的减小而减小,当弱面强度较高时,起裂压力大于裂隙条件下的起裂压力,而且沿着基质起裂;当注浆孔置于弱面两端或裂隙中间时,起裂裂隙沿弱面或裂隙的两端起裂,当注浆孔置于弱面中间位置时,起裂裂隙沿中间位置的基质起裂。研究结果有助于底板水害超前区域改造劈裂注浆的有效控制,指导注浆参数的选取,为解放深部煤炭资源提供技术支撑。

基于PFC2D的综放开采顶煤冒放规律数值模拟

为了更加形象地研究顶煤冒放形态特征、宏观地把破碎的散体看作非理想状态下随机流动的松散介质.以某矿1302N大采高综放工作面为工程背景,利用离散元散体颗粒流软件PFC2D建立放顶煤二维横剖面模型,主要研究顶煤位移、煤矸动场变化、放出体衍化以及超前支承压力分布等现象.研究对比得出:顶煤流动规律方面,走向上放煤步距增大,顶煤的始动点边界线前移,顶煤运移范围增大;倾向上间隔放煤的煤损主要集中于同一轮放煤支架间的漏斗煤损.煤矸流场规律方面,采高增大煤矸分界线逐渐变陡;放煤步距增大,煤矸分界线始终保持双线形态前移.矿压显现规律方面,顶煤的硬度增大,顶煤分区中范围逐渐缩小,即超前支承压力峰值区向煤壁靠拢;采放比增大,超前支承压力峰值区远离煤壁,综放开采顶煤破碎后的流动特点和运移路径的数值模拟研究,有利于掌握散体顶煤的放出规律,据此对放煤工艺参数进行针对性的优化设计,对提高煤炭资源采出率具有重要意义.

Microdamage study of granite under thermomechanical coupling based on the particle flow code

The thermomechanical coupling of rocks refers to the interaction between the mechanical and thermodynamic behaviors of rocks induced by temperature changes.The study of this coupling interaction is essential for understanding the mechanical and thermodynamic properties of the surrounding rocks in underground engineering.In this study,an improved temperature-dependent linear parallel bond model is introduced under the framework of a particle flow simulation.A series of numerical thermomechanical coupling tests are then conducted to calibrate the micro-parameters of the proposed model by considering the mechanical behavior of the rock under different thermomechanical loadings.Good agreement between the numerical results and experimental data are obtained,particularly in terms of the compression,tension,and elastic responses of granite.With this improved model,the thermodynamic response and underlying cracking behavior of a deep-buried tunnel under different thermal loading conditions are investigated and discussed in detail.

Study on disc cutter chipping of TBM based on field data and particle flow code simulation

Using tunnel boring machines to excavate high-strength intact rock masses is becoming more common.Due to the interactions between disc cutters and rocks,abnormal wear of disc cutters,especially cutter chipping,has become a common phenomenon.Existing research has mainly focused on normal wear of disc cutters without addressing abnormal wear cases.This study used the disc cutter consumption data of a tunnel project in China to investigate the abovementioned problem based on field research.According to the fail-ure patterns and fracture surface characteristics,the cutter chipping patterns were mainly categorized into four types:granule chipping,patch chipping,primary collapse,and secondary collapse.To further simulate the evolution of disc cutter chipping,based on the linear plastic bond model,a new contact model called the modified plastic bond(MPB)model was proposed to solve the metal simulation prob-lem in Particle Flow Code software.To this end,a set of uniaxial tensile and compressive tests were initially conducted to verify the applicability of the MPB model.Then,a series of three-dimensional rock-cutting simulation tests were conducted to reflect the evolu-tionary processes involved in each type of cutter chipping.The cutter chipping mechanism and morphological characteristics were clas-sified and summarized in detail.The results revealed that the cutting speed and penetration growth led to a rising trend in the probability and intensity of the cutter chipping.The presence of initial defects also induced an adverse effect on the service life of the cutter.The results indicated suitable working conditions for the cutter and suggested ways to control tunneling parameters and avoid frequent cutter chipping cases.

隧道围岩-衬砌接触面剪切特性模拟研究

探究隧道围岩-衬砌接触面在不同法向应力及不同粗糙度条件下的剪切特性规律,对进一步研究隧道围岩与衬砌间的相互作用及岩体稳定性具有重要的理论和工程意义。为考虑粗糙度条件,利用分形理论,通过改变分形公式中的分形维数D及分形粗糙度G生成5种不同接触面,基于二维颗粒流程序(PFC^(2D)),建立接触面数值剪切模型,尺寸为150 mm×150 mm。开展同一接触面在不同法向应力下,数值模拟剪切试验及不同接触面在同一法向应力下的数值模拟试验;将数值剪切试验与室内剪切试验获得的剪切应力-剪切位移曲线进行对比,验证数值剪切模拟的可靠性。研究结果表明:(1)数值模型剪切破坏产生的裂隙主要集中于中间接触面处,破坏后的应力主要集中于接触面粗糙度最大处,破坏裂纹可分为剪切裂纹和张拉裂纹,其中张拉裂纹占主要优势;(2)剪切应力-剪切位移过程曲线存在爬坡、啃断、滑移三大阶段,具有明显的峰值强度和残余强度,法向位移随着剪切位移的增加而增大,产生剪胀效应;(3)随着法向应力增加,剪切和张拉裂纹数量增加,破坏现象越明显,峰值强度和残余强度增大,剪胀效应减小;(4)随着粗糙起伏度增大,即分形维数D的增大或者分形粗糙度G的减小,破坏裂纹数量增加,其中张拉裂纹增加较明显,峰值强度和残余强度增大,剪胀效应增大。

正交-响应面法在PBM细观参数标定中的应用

数值模拟作为研究岩石力学特性、再现细观裂纹演化的主要途径,已受到大量关注。现有的数值模拟参数标定方法主要为试错法及正交试验法,但二者都未能充分考虑细观参数交互作用的影响,模拟精度欠佳且宏观破坏形态与室内试验存在较大差异。因此,采用正交-响应面法相结合的数值分析方法,首先通过正交试验筛选出具有显著影响的平行黏结模型(PBM)细观参数,其次应用响应面法(RSM)研究其交互作用对模型试样宏观参量的影响规律,最后结合岩石宏观破坏形态提出一套PBM参数标定流程。结果表明:有效模量E*与刚度比k n/k s对弹性模量E影响显著;k n/k s、接触摩擦系数μ、最小颗粒半径R_(min)对泊松比ν影响显著;黏聚力c与法向黏结强度σc及其交互作用对单轴抗压强度UCS影响显著,应用响应面法计算分析得出的细观参数的模拟值与试验值误差绝对值小于7%,且二者应力应变曲线力学特征相似,宏观破坏形态相同,证明所提出的PBM细观参数标定流程具备科学性和可靠性。

断续节理直剪试验与PFC^2D数值模拟分析

在以往有关断续节理模型试验和数值模拟的研究基础上,设计不同连通情况和法向应力的断续节理模型材料直剪试验,并采用颗粒流离散元软件PFC2D对模型试验进行全真数值模拟。以贯通节理试样、完整试样的剪应力–应变数值模拟曲线和模型试验曲线吻合作为PFC细观力学参数选取准则,并利用获得的细观力学参数对共面断续节理试样直剪试验进行数值重现。对比分析数值模拟曲线和模型试验曲线,对断续节理受剪贯通的力学机制进行研究。根据模型试验和数值试验的成果,分析断续节理预剪面上应力随剪应变的演化过程,发现剪切过程中的剪胀效应使得岩桥承担更多的压应力,从而提高了岩桥的抗剪强度。对断续节理岩体在直剪加载条件下的破坏机制进行讨论,将整个剪切过程分为线弹性阶段、初裂阶段、峰值阶段、峰后阶段及残余阶段5个阶段。

PFC滑坡模拟二、三维建模方法研究

滑坡运动过程模拟避免了试验尺度与监测手段的限制,可以详细观察破坏过程,是定量评估滑坡灾变风险的重要研究手段。开展滑坡运动过程模拟的首要工作是建立滑坡模型。颗粒流程序(PFC)虽然是滑坡运动过程模拟应用最广泛的程序之一,但在建立滑坡模型的前处理方面较弱,使得其在滑坡运动过程模拟中的推广应用受到限制。对此,本文指出了BallBall和Ball-Wall两种建模方法的适用性、优缺点及滑体滑床边界确定方法,并以2014年地震触发的红石岩滑坡为例,以Brick填充法为基础,从获取地形数据、确定滑体和滑床区域、建立滑体和滑床几何模型、生成颗粒模型4个步骤出发,提出了基于数字等高线地形图建立PFC二、三维复杂滑坡模型的前处理方法,弥补了PFC软件前处理的不足,从而为今后基于PFC的滑坡运动过程模拟提供有益的帮助。

泥石流启动过程PFC数值模拟

泥石流松散碎屑物质具有散粒体的基本特征,在暴雨激发下容易形成泥石流,整个过程具有散粒体大变形的特征。颗粒流理论是基于离散单元法模拟圆形颗粒介质的运动及其相互作用,在模拟颗粒相互作用和大变形问题研究方面具有显著的优越性。为分析泥石流松散碎屑物质启动形成泥石流的过程及其与土体含水率的关系,采用二维颗粒流程序(PFC2D)分析降雨作用下松散碎屑物质启动形成泥石流的过程,揭示崩滑堆积体在降雨作用下含水率超过临界值后质点运动速度和位移增加,松散碎屑物质启动并加速而导致滑坡泥石流连锁式破坏的过程和机制。

不同加载速率下青砂岩破裂演化规律及能量利用效率分析

【目的】研究不同加载速率下岩石破裂演化规律及能量利用效率是岩石破碎加工领域亟待解决的问题。【方法】基于室内试验进行青砂岩细观参数标定,建立青砂岩宏-细观力学响应关系,采用颗粒流程序,研究不同加载速率下青砂岩应力-应变曲线与应力链分布特征,从破裂特征与裂纹特点方面分析青砂岩的破裂演化规律,并分析青砂岩破裂过程中的能量利用效率。【结果和结论】结果表明:(1)青砂岩在破裂过程中,应力-应变曲线表现为峰前线弹性、峰前塑性变形和峰后逐步失稳阶段,拉力链导致青砂岩裂纹扩展,最终破裂是压力和拉力链相互作用的结果。(2)不同加载速率下,青砂岩破裂可分为剪切破裂、贯穿破裂及混合多级破裂阶段,剪切与贯穿破裂阶段是剪切力起主要作用,而混合多级破裂是拉伸力主导的破裂模式。拉伸裂纹在破裂过程中起主导作用,生成速率明显高于剪切裂纹,总裂纹生成速率达2 400.81 m/s。(3)青砂岩断裂能的演化可分为缓慢增加、急剧增大与趋于稳定阶段,在加载速率为0.05 m/s时,最大能量利用效率为0.088%。研究结果不仅从细观层面对岩石破裂演化规律及能量利用效率进行了初步探索,也可为岩石破碎过程中工艺参数的合理选择提供指导。

鸡尾山高速远程滑坡运动过程PFC^(3D)模拟

利用三维颗粒流软件PFC3D,对重庆武隆鸡尾山滑坡进行模拟,研究滑坡体在关键块体失稳后,在重力作用下,沿着滑动面在视倾向滑动力主导下的运动过程。结果显示:(1)对于大型远距离滑坡,在滑坡体运动路径上坡面形态确定的情况下,坡面摩擦因数和滑体强度主要影响堆积颗粒在滑坡堆积区的分布,滑坡发生区域微地形则更多地影响滑坡体所能达到的最大位移;(2)鸡尾山高速远程滑坡的发生过程是分阶段完成的;第一阶段主要是滑源区岩体的破裂化,第二阶段为破裂块体的运动及滑出;(3)通过监测速度、位移等发现滑体外围区域块体速度首先达到最大值,并具备二次加速的特征,综合速度及位移可以认为在滑体中处于上部边缘部分更有可能远距离运动;(4)对于鸡尾山滑坡,当墙面摩擦因数为0.05,黏结强度为中等(250～200 MPa)时,得到的结果与实际情形最为契合。通过模拟发现,PFC3D软件对于此类高速远程滑坡具有较好的适用性,尤其是其三维堆积形态及影响范围的初步确定可以对划定安全避让范围等防灾减灾工作提供有益参考。

PFC^(3D)模型中砂土细观参数的确定方法

采用理论分析和数值仿真试验相结合的方法,对砂性土的的细观参数与宏观参数间的对应关系进行了研究。在总结大量三维颗粒流数值试验结果基础上,提出了与砂土的孔隙率、内摩擦角及压缩模量等宏观力学参数相匹配的细观参数的确定方法,并给出了细观结构参数与宏观力学参数的函数关系。根据确立的砂土细观参数,建立了桩基础的三维颗粒流数值分析模型,实现了桩基础荷载–沉降特性及桩周土体位移场的仿真模拟,且模拟结果与室内模型试验具有良好的一致性,验证了细观参数确定方法及结果的可靠性。研究成果为后续的桩–土–承台细观工作性状研究工作的开展奠定了坚实的基础。