This study investigated the effects of weathering depth and thickness on the failure mechanisms of rock samples through experimental and numerical methods.The first configuration involved conducting artificial weather...This study investigated the effects of weathering depth and thickness on the failure mechanisms of rock samples through experimental and numerical methods.The first configuration involved conducting artificial weathering on limestone using the freezing and thawing(F-T)for 40 cycles.The mechanical parameters of the samples were measured at the end of the 40th cycle.In the second configuration,a series of specimens underwent salt crystallization(S-C)tests for 20 cycles.Experimental results were validated using discrete element method(DEM).Next,the weathered limestone model with dimensions of 108 mm54 mm were prepared.The weathering layers were tested at four different thicknesses(i.e.2.5 mm,5 mm,7.5 mm,and 10 mm)and three different positions(at the surface,5 mm under the rock surface,and 10 mm under the rock surface).According to the results,weathering depth and thickness have a considerable effect on the failure process.The results also showed a correlation between the values of compressive strength and failure mechanisms associated with the weathering layer.The numerical results revealed that the tension crack was the dominant factor.Additionally,with increasing weathering thickness,Young's modulus,crack initiation stress,and final strength decreased in constant weathering depth.The results also demonstrated that the failure progress of the numerical models was similar to that observed in the laboratory.展开更多
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 fis...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.展开更多
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...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.展开更多
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 rain...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.展开更多
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. Th...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.展开更多
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...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.展开更多
A two-dimensionM discrete element code, particle flow code （PFC2D）, is employed to investigate foundations reinforced with horizontal-vertical （H-V） inclusions. The initial states and loading processes of both unr...A two-dimensionM discrete element code, particle flow code （PFC2D）, is employed to investigate foundations reinforced with horizontal-vertical （H-V） inclusions. The initial states and loading processes of both unreinforced and H-V reinforced foundations are simulated by PFC2D method. The interface between particles and reinforcements, and the reinforcement mechanism of the H-V reinforced foundations are studied through stress distribution graphs, displacement vector graphs and contact force graphs. The simulation results demonstrate that the vertical elements of the H-V reinforcement keep the particles from being displaced under the applied load. The H-V reinforcement can distribute the load uniformly over a wider area, thereby improving the bearing capacity of soil foundation.展开更多
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 under...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.展开更多
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 bec...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.展开更多
Structure-type rockbursts frequently occur in deep tunnels,with structural planes and stress conditions being critical factors in their formation.In this study,we utilized specially developed analogous materials that ...Structure-type rockbursts frequently occur in deep tunnels,with structural planes and stress conditions being critical factors in their formation.In this study,we utilized specially developed analogous materials that exhibit the high brittleness and strength characteristics of deep hard rock to construct physical models representing different types of structural planes,including composite,exposed,non-exposed,and throughgoing structural planes.Physical simulation experiments were conducted on structuretype rockbursts in deep horseshoe-shaped tunnels,focusing on strain differentiation characteristics,critical triggering conditions,critical crack opening displacement,the incubation process,the reduction effects of structural planes on failure intensity,and formation mechanisms.These experiments were complemented by acoustic and optical monitoring,as well as discrete element numerical simulations,to provide a comprehensive analysis.The results revealed that the most significant strain heterogeneity in the surrounding rock occurs at the tip of the structural plane along the tunnel's minimum principal stress direction,driven by the combined effects of tensile and shear forces.We quantitatively determined the critical stress and strain conditions for structure-type rockbursts and evaluated the intensity of rockbursts induced by different structural planes using critical crack opening displacement(COD)values,the uniformity coefficient,and the curvature coefficient.Analysis of acoustic emission events,including frequency,amplitude,and b-value,indicated that the macro-fracture process is governed by both the principal stress differential and the characteristics of the structural plane.Furthermore,using the bearing capacity reduction coefficient,we found that exposed structural planes have the most significant weakening effect on rock mass strength,followed by non-exposed and throughgoing structural planes.The analysis of average frequency(AF)and rise angle(RA)parameters revealed a close correlation between the failure modes of structure-type rockbursts,the rock mass structure,and the stress levels.These findings provide critical theoretical support for the prediction and prevention of structure-type rockburst disasters.展开更多
Microbially induced calcium carbonate precipitation(MICP)technology can induce calcium carbonate crystals with cementation and stable performance in the process of microbial metabolism or enzymization through the regu...Microbially induced calcium carbonate precipitation(MICP)technology can induce calcium carbonate crystals with cementation and stable performance in the process of microbial metabolism or enzymization through the regulation of environmental factors MICP can be used as a cementing agent to cement cohesionless sand particles to form the materials with the characteristics of higher strength,better durability and environmental friendli-ness,as well as a good engineering application prospect.In this paper,the shear strength of sand column was tested by triaxial compression tests,and the strength index was obtained.In order to further study the micro-strength mechanism and the failure process,based on the discrete element method,a numerical model of MICP cemented sand column was established considering the factors of matrix soil particle gradation,particle mor-phology,content ratio of induced calcium carbonate,pore distribution characteristics,inter-particle cementation and so on.The failure process of MICP cemented sand column under load was analysed by numerical simulation,and the reliability of the numerical model was tested by combining with the stress intensity curve of samples under test conditions.The results indicate that compared with the actual triaxial tests of MICP cemented sand column,although there are deviations in stress and strain,cohesion and internal friction angle,the numerical simulation shows similar development law and intensity amplitude,and the same failure trend.The work in this paper verifies the reliability of the numerical model and provides a theoretical basis for the subsequent analysis of the factors influencing the geotechnical mechanical properties of biomineralized materials.展开更多
Fissured coal mass under triaxial unloading condition exhibits higher burst potential than the triaxial loading condition,which poses challenge to safety and productivity of resources extraction and underground space ...Fissured coal mass under triaxial unloading condition exhibits higher burst potential than the triaxial loading condition,which poses challenge to safety and productivity of resources extraction and underground space utilization.To comprehensively understand the mechanism of unloading-induced burst during excavation process,this study investigated the fracture and energy evolution of samples with different fissure types such as single,two parallel,and two coplanar-parallel using PFC2D modelling.Triaxial loading tests were conducted to determine the compressive strengths and other parameters.With increase of fissure inclination angle,the triaxial compressive strength decreases forβ=0°-30°,and then increase forβ=30°-90°.The strength of samples with two coplanar-parallel fissures is the highest.Fissure can significantly change the distribution of fracture and elastic energy.Secondary cracks were generated starting from both ends of the fissure.Forβ=0°-60°,low elastic strain energy area was produced around the fissure along the loading direction.The elastic strain energy is transferred to the outside of fissures.Forβ=75°-90°,only a small amount of high elastic strain energy was generated on both sides of the fissure.The fracture expansion under unloading conditions occurred due to tensile stress T caused by unloading differential rebound deformation and the shear stress on the fissure surface.展开更多
The mechanical properties of rocks weaken under dry-wet cycles.This weakening may significantly modify the safety reserve of underground caverns or reservoir bank slopes.However,meso-damage has not been carefully stud...The mechanical properties of rocks weaken under dry-wet cycles.This weakening may significantly modify the safety reserve of underground caverns or reservoir bank slopes.However,meso-damage has not been carefully studied based on micromechanical observations and analyses.Therefore,in this study,meso-damage of a yellow sandstone is investigated and a meso-damage-based constitutive model for dry-wet cycles is proposed.First,computed tomography scanning and uniaxial compression tests were conducted on yellow sandstones under different dry-wet cycles.Second,the evolution of rock mesostructures and the damage mechanism subjected to dry-wet cycles were simulated using the discrete element method with Particle Flow Code in 2 Dimensions(PFC2D)software.Third,a constitutive model was proposed based on the meso-statistical theory and damage mechanics.Finally,this constitutive model was verified with the experimental results to check its prediction capability.It is found that the radius and number of pore throats in the sandstone increase gradually with the number of dry-wet cycles,and the pore structure connectivity is also improved.The contact force of sandstone interparticle cementation decreases approximately linearly and the continuity of the particle contact network is continuously broken.The meso-deformation and strength parameters show similar declining patterns to the modulus of elasticity and peak strength of the rock sample,respectively.This meso-damage-based constitutive model can describe well the rock deforma-tion in the initial pressure density stage and the damage stage under the coupling effect of dry-wet cycles and loads.展开更多
The Fenwei Basin, covered by loess, experiences severe ground fissure disasters. These disasters disrupt the continuity of the loess and pose significant threats to engineering construction safety along transportation...The Fenwei Basin, covered by loess, experiences severe ground fissure disasters. These disasters disrupt the continuity of the loess and pose significant threats to engineering construction safety along transportation routes. Nevertheless, the crack characteristics and the influence zone of ground fissures in the loess layer remain inadequately investigated. To effectively prevent and control ground fissure disasters, physical model tests and the PFC(particle flow code) numerical simulation method are used to investigate the crack mechanism of buried ground fissures in the loess layer. The results show that there are two main cracks in the layer profile, which have a Y-shape morphology. As the dip angle of the preset cracks increased from 60° to 90°, the main deformation zone at the surface gradually shifted towards the footwall. The process of crack propagation from depth to surface is divided into five stages. Additionally, the results confirm the accuracy of the width of the rupture zone d2in the footwall calculated by the cantilever beam theory. These findings can offer theoretical guidance for determining the avoidance distance of ground fissures in loess regions, as well as for implementing disaster prevention and corresponding control measures for various stages of buried ground fissure propagation.展开更多
From a practical point of view,grain structure heterogeneities are key parameters that control the rock response and still remains a challenge to incorporate in a quantitative manner.One of the less discussed topics i...From a practical point of view,grain structure heterogeneities are key parameters that control the rock response and still remains a challenge to incorporate in a quantitative manner.One of the less discussed topics in the context of the grain-based model(GBM)in the particle flow code(PFC)is the contact heterogeneities and the appropriate contact model to mimic the grain boundary behavior.Generally,the smooth joint(SJ)model and linear parallel bond(LPB)model are used to simulate the grain boundary behavior.However,the literature does not document the suitability of different models for specific problems.Another challenge in implementing GBM in PFC is that only a single bonding parameter is used at the grain boundaries.The aim of this study is to investigate the responses of a laboratory-scale specimen with SJ and LPB models,considering grain boundary heterogeneous and homogeneous contact parameters.Uniaxial and biaxial compression tests are performed to calibrate the response of Creighton granite.The stressestrain curves,volumetric dilation,inter-crack(crack in the grain boundary),and intra-crack(crack within the grain)development,and failure patterns associated with different contact models are examined.It was found that both the SJ and LPB models can reproduce the pre-peak behavior observed for a granitic rock type.However,the LPB model is unable to reproduce the post-peak behavior.Due to the large interlocking effect originating from the balls in contact and the ball size in the LPB model,local dilation is induced at the grain boundaries.This overestimates the volumetric dilation and residual shear strength.The LPB model tends to result in discontinuous inter-cracks and stress localization in the rock specimen,resulting in fine fragments at the rock surface during failure.展开更多
In this paper,Brazilian test was performed on disk samples of analogue materials with defined structural planes.The surface strain evolution process of the disk samples during loading was analyzed via digital image co...In this paper,Brazilian test was performed on disk samples of analogue materials with defined structural planes.The surface strain evolution process of the disk samples during loading was analyzed via digital image correlation.The damage evolution process was explored from a microscopic perspective by combining discrete element numerical simulation technology.The criterion of the failure mode of the disc specimen in the split state was theoretically deduced.The influence of structural surface roughness and loading inclination angle on the stress state at the center of the specimen was explored.The results showed that the failure modes of the samples could be divided into three typical modes as matrix failure,structural plane failure and combination failure.The rough structural plane improves the failure strength of the specimen by limiting its lateral deformation,and the degree of improvement weakens continuously with the increase of the inclination angle of the structural plane.As the inclination angle of the structural plane increases,the main type of microcracks in the structural plane changes from shear microcracks to tensile microcracks.This study contributes to a better understanding of macro-and meso-failure characteristics of rock masses with structural planes under a splitting state.展开更多
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 m...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.展开更多
Hydraulic fracturing,as a key technology of deep energy exploitation,accelerates the rapid development of the modern petroleum industry.To study the mechanisms of hydraulic fracture propagation and rock failure mode o...Hydraulic fracturing,as a key technology of deep energy exploitation,accelerates the rapid development of the modern petroleum industry.To study the mechanisms of hydraulic fracture propagation and rock failure mode of the vertical well hydraulic fracturing,the true triaxial hydraulic fracturing test and numerical simulation are carried out,and the influence of the principal stress difference,water injection displacement,perforation angle and natural fracture on fracture propagation is analyzed.The results show that the fracture propagation mode of limestone is mainly divided into two types:the single vertical fracture and the transverse-longitudinal crossed complex fracture.Under high displacement,the fracturing pressure is larger,and the secondary fracture is more likely to occur,while variable displacement loading is more likely to induce fracture network.Meanwhile,the amplitude of acoustic emission(AE)waveform of limestone during fracturing is between 0.01 and 0.02 mV,and the main frequency is maintained in the range of 230−300 kHz.When perforation angleθ=45°,it is easy to produce the T-type fracture that connects with the natural fracture,while X-type cracks are generated whenθ=30°.The results can be used as a reference for further study on the mechanism of limestone hydraulic fracturing.展开更多
文摘This study investigated the effects of weathering depth and thickness on the failure mechanisms of rock samples through experimental and numerical methods.The first configuration involved conducting artificial weathering on limestone using the freezing and thawing(F-T)for 40 cycles.The mechanical parameters of the samples were measured at the end of the 40th cycle.In the second configuration,a series of specimens underwent salt crystallization(S-C)tests for 20 cycles.Experimental results were validated using discrete element method(DEM).Next,the weathered limestone model with dimensions of 108 mm54 mm were prepared.The weathering layers were tested at four different thicknesses(i.e.2.5 mm,5 mm,7.5 mm,and 10 mm)and three different positions(at the surface,5 mm under the rock surface,and 10 mm under the rock surface).According to the results,weathering depth and thickness have a considerable effect on the failure process.The results also showed a correlation between the values of compressive strength and failure mechanisms associated with the weathering layer.The numerical results revealed that the tension crack was the dominant factor.Additionally,with increasing weathering thickness,Young's modulus,crack initiation stress,and final strength decreased in constant weathering depth.The results also demonstrated that the failure progress of the numerical models was similar to that observed in the laboratory.
基金The University of Vigo is acknowledged for financing part of the first author’s PhD studiesthe Spanish Ministry of Economy and Competitiveness for funding of the project‘Deepening on the behaviour of rock masses:Scale effects on the stressestrain response of fissured rock samples with particular emphasis on post-failure’,awarded under Contract Reference No.RTI2018-093563-B-I00partially financed by means of European Regional Development Funds from the European Union(EU)。
文摘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.
基金Project（BK20150005） supported by the Natural Science Foundation of Jiangsu Province for Distinguished Young Scholars, China Project（2015XKZD05） supported by the Fundamental Research Funds for the Central Universities, China
文摘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.
基金The National Natural Science Foundation of China(Grants Nos.51309089,41472272 and 11202063)the National Key Technology R&D Program(Grant No.2013BAB06B00)+1 种基金the Natural Science Foundation of Jiangsu Province(Grant No.BK20130846)the Fundamental Research Funds for the Central Universities(Grant No.2015B06014)supported this work
文摘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.
基金the National Key R&D Program of China(No.2017YFC0405002)
文摘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.
基金financially supported by the National Natural Science Foundation of China(Nos.51874229,52074212,51674188,51504182,51404191,and 51405381)the Natural Science Basic Research Plan of Shaanxi Province of China(Nos.2015JQ5187,2018JQ5183,and 2018JM5161)+3 种基金the Scientific Research Program funded by the Shaanxi Education Department(No.15JK1466)the China Postdoctoral Science Foundation(No.2015M582685)the Outstanding Youth Science Fund of Xi’an University of Science and Technology(No.2018YQ2-01)supported by the National Research Council of Science&and Technology(NST)grant by the Korea Korean government(MSIP)(No.CRC-16-38502-KICT)。
文摘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.
基金the National Natural Science Foundation of China (Nos. 41202215 and 40972192)the Innovation Program of Shanghai Municipal Education Commission (No. 11ZZ88)the Innovation Foundation of Shanghai University
文摘A two-dimensionM discrete element code, particle flow code （PFC2D）, is employed to investigate foundations reinforced with horizontal-vertical （H-V） inclusions. The initial states and loading processes of both unreinforced and H-V reinforced foundations are simulated by PFC2D method. The interface between particles and reinforcements, and the reinforcement mechanism of the H-V reinforced foundations are studied through stress distribution graphs, displacement vector graphs and contact force graphs. The simulation results demonstrate that the vertical elements of the H-V reinforcement keep the particles from being displaced under the applied load. The H-V reinforcement can distribute the load uniformly over a wider area, thereby improving the bearing capacity of soil foundation.
基金supported by the Postgraduate Research&Practice Innovation Program of Jiangsu Province (No.KYCX21_0494)the National Natural Science Foundation of China (Grant Nos.51679071 and 41831278)the Key Laboratory of the Ministry of Education on Safe Mining of Deep Metal Mines (No.DM2019K02).
文摘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.
基金supported by the National Natural Science Foundation of China(Grant No.52078377)the Key Field Science and Technology Project of Yunnan Province(Grant No.202002AC080002)supported by the China Atomic Energy Authority(CAEA)through the Geological Disposal Program.
文摘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.
基金supported by the National Natural Science Foundation of China(Grant Nos.42307241 and 42107211)the State Key Laboratory of Geohazard Prevention and Geoenvironment Protection Independent Research Project(Grant No.SKLGP2022Z008).
文摘Structure-type rockbursts frequently occur in deep tunnels,with structural planes and stress conditions being critical factors in their formation.In this study,we utilized specially developed analogous materials that exhibit the high brittleness and strength characteristics of deep hard rock to construct physical models representing different types of structural planes,including composite,exposed,non-exposed,and throughgoing structural planes.Physical simulation experiments were conducted on structuretype rockbursts in deep horseshoe-shaped tunnels,focusing on strain differentiation characteristics,critical triggering conditions,critical crack opening displacement,the incubation process,the reduction effects of structural planes on failure intensity,and formation mechanisms.These experiments were complemented by acoustic and optical monitoring,as well as discrete element numerical simulations,to provide a comprehensive analysis.The results revealed that the most significant strain heterogeneity in the surrounding rock occurs at the tip of the structural plane along the tunnel's minimum principal stress direction,driven by the combined effects of tensile and shear forces.We quantitatively determined the critical stress and strain conditions for structure-type rockbursts and evaluated the intensity of rockbursts induced by different structural planes using critical crack opening displacement(COD)values,the uniformity coefficient,and the curvature coefficient.Analysis of acoustic emission events,including frequency,amplitude,and b-value,indicated that the macro-fracture process is governed by both the principal stress differential and the characteristics of the structural plane.Furthermore,using the bearing capacity reduction coefficient,we found that exposed structural planes have the most significant weakening effect on rock mass strength,followed by non-exposed and throughgoing structural planes.The analysis of average frequency(AF)and rise angle(RA)parameters revealed a close correlation between the failure modes of structure-type rockbursts,the rock mass structure,and the stress levels.These findings provide critical theoretical support for the prediction and prevention of structure-type rockburst disasters.
基金sponsored by the National Natural Science Foundation of China(Grant No.12002173,12262027)Research start-up project of Inner Mongolia University of Technology(No.2200000924)key Lab.of University of Geological Hazards and Geotechnical Engineering Defense in Sandy and Drought Regions,Inner Mongolia Autonomous.
文摘Microbially induced calcium carbonate precipitation(MICP)technology can induce calcium carbonate crystals with cementation and stable performance in the process of microbial metabolism or enzymization through the regulation of environmental factors MICP can be used as a cementing agent to cement cohesionless sand particles to form the materials with the characteristics of higher strength,better durability and environmental friendli-ness,as well as a good engineering application prospect.In this paper,the shear strength of sand column was tested by triaxial compression tests,and the strength index was obtained.In order to further study the micro-strength mechanism and the failure process,based on the discrete element method,a numerical model of MICP cemented sand column was established considering the factors of matrix soil particle gradation,particle mor-phology,content ratio of induced calcium carbonate,pore distribution characteristics,inter-particle cementation and so on.The failure process of MICP cemented sand column under load was analysed by numerical simulation,and the reliability of the numerical model was tested by combining with the stress intensity curve of samples under test conditions.The results indicate that compared with the actual triaxial tests of MICP cemented sand column,although there are deviations in stress and strain,cohesion and internal friction angle,the numerical simulation shows similar development law and intensity amplitude,and the same failure trend.The work in this paper verifies the reliability of the numerical model and provides a theoretical basis for the subsequent analysis of the factors influencing the geotechnical mechanical properties of biomineralized materials.
基金supported by the National Science and Technology Major Project(2024ZD1000705)the Basic Research Project of Liaoning Provincial Department of Education-Key Project of Independent Topic Selection(LJ212410147007).
文摘Fissured coal mass under triaxial unloading condition exhibits higher burst potential than the triaxial loading condition,which poses challenge to safety and productivity of resources extraction and underground space utilization.To comprehensively understand the mechanism of unloading-induced burst during excavation process,this study investigated the fracture and energy evolution of samples with different fissure types such as single,two parallel,and two coplanar-parallel using PFC2D modelling.Triaxial loading tests were conducted to determine the compressive strengths and other parameters.With increase of fissure inclination angle,the triaxial compressive strength decreases forβ=0°-30°,and then increase forβ=30°-90°.The strength of samples with two coplanar-parallel fissures is the highest.Fissure can significantly change the distribution of fracture and elastic energy.Secondary cracks were generated starting from both ends of the fissure.Forβ=0°-60°,low elastic strain energy area was produced around the fissure along the loading direction.The elastic strain energy is transferred to the outside of fissures.Forβ=75°-90°,only a small amount of high elastic strain energy was generated on both sides of the fissure.The fracture expansion under unloading conditions occurred due to tensile stress T caused by unloading differential rebound deformation and the shear stress on the fissure surface.
基金The Geological Safety of Underground Space in Coastal Cities,Ministry of Natural Resources Key Laboratory Open Fund,Grant/Award Number:BHKF2022Y03。
文摘The mechanical properties of rocks weaken under dry-wet cycles.This weakening may significantly modify the safety reserve of underground caverns or reservoir bank slopes.However,meso-damage has not been carefully studied based on micromechanical observations and analyses.Therefore,in this study,meso-damage of a yellow sandstone is investigated and a meso-damage-based constitutive model for dry-wet cycles is proposed.First,computed tomography scanning and uniaxial compression tests were conducted on yellow sandstones under different dry-wet cycles.Second,the evolution of rock mesostructures and the damage mechanism subjected to dry-wet cycles were simulated using the discrete element method with Particle Flow Code in 2 Dimensions(PFC2D)software.Third,a constitutive model was proposed based on the meso-statistical theory and damage mechanics.Finally,this constitutive model was verified with the experimental results to check its prediction capability.It is found that the radius and number of pore throats in the sandstone increase gradually with the number of dry-wet cycles,and the pore structure connectivity is also improved.The contact force of sandstone interparticle cementation decreases approximately linearly and the continuity of the particle contact network is continuously broken.The meso-deformation and strength parameters show similar declining patterns to the modulus of elasticity and peak strength of the rock sample,respectively.This meso-damage-based constitutive model can describe well the rock deforma-tion in the initial pressure density stage and the damage stage under the coupling effect of dry-wet cycles and loads.
基金supported by National Natural Science Foundation of China (Grant NOs. 41877250, 41272284)the Key Laboratory of Earth Fissures Geological Disaster, Ministry of Natural Resources (No. EFGD20240601)the Natural Science Foundation of Shaanxi Province-General Project (grant number 2023-JC-YB-231)-Suitability Evaluation of Precast Prestressed Underground Comprehensive Pipe Gallery Crossing Active Ground Fissure。
文摘The Fenwei Basin, covered by loess, experiences severe ground fissure disasters. These disasters disrupt the continuity of the loess and pose significant threats to engineering construction safety along transportation routes. Nevertheless, the crack characteristics and the influence zone of ground fissures in the loess layer remain inadequately investigated. To effectively prevent and control ground fissure disasters, physical model tests and the PFC(particle flow code) numerical simulation method are used to investigate the crack mechanism of buried ground fissures in the loess layer. The results show that there are two main cracks in the layer profile, which have a Y-shape morphology. As the dip angle of the preset cracks increased from 60° to 90°, the main deformation zone at the surface gradually shifted towards the footwall. The process of crack propagation from depth to surface is divided into five stages. Additionally, the results confirm the accuracy of the width of the rupture zone d2in the footwall calculated by the cantilever beam theory. These findings can offer theoretical guidance for determining the avoidance distance of ground fissures in loess regions, as well as for implementing disaster prevention and corresponding control measures for various stages of buried ground fissure propagation.
基金Supports from the University Transportation Center for Underground Transportation Infrastructure(UTC-UTI)at the Colorado School of Mines for funding this research under Grant No.69A3551747118 from the US Department of Transportation(DOT)the Fundamental Research Funds for the Central Universities under Grant No.A0920502052401-210 are gratefully acknowledged.
文摘From a practical point of view,grain structure heterogeneities are key parameters that control the rock response and still remains a challenge to incorporate in a quantitative manner.One of the less discussed topics in the context of the grain-based model(GBM)in the particle flow code(PFC)is the contact heterogeneities and the appropriate contact model to mimic the grain boundary behavior.Generally,the smooth joint(SJ)model and linear parallel bond(LPB)model are used to simulate the grain boundary behavior.However,the literature does not document the suitability of different models for specific problems.Another challenge in implementing GBM in PFC is that only a single bonding parameter is used at the grain boundaries.The aim of this study is to investigate the responses of a laboratory-scale specimen with SJ and LPB models,considering grain boundary heterogeneous and homogeneous contact parameters.Uniaxial and biaxial compression tests are performed to calibrate the response of Creighton granite.The stressestrain curves,volumetric dilation,inter-crack(crack in the grain boundary),and intra-crack(crack within the grain)development,and failure patterns associated with different contact models are examined.It was found that both the SJ and LPB models can reproduce the pre-peak behavior observed for a granitic rock type.However,the LPB model is unable to reproduce the post-peak behavior.Due to the large interlocking effect originating from the balls in contact and the ball size in the LPB model,local dilation is induced at the grain boundaries.This overestimates the volumetric dilation and residual shear strength.The LPB model tends to result in discontinuous inter-cracks and stress localization in the rock specimen,resulting in fine fragments at the rock surface during failure.
基金Project(52274148)supported by the National Natural Science Foundation of ChinaProject(2022XJLJ01)supported by the Fundamental Research Funds for the Central Universities,China。
文摘In this paper,Brazilian test was performed on disk samples of analogue materials with defined structural planes.The surface strain evolution process of the disk samples during loading was analyzed via digital image correlation.The damage evolution process was explored from a microscopic perspective by combining discrete element numerical simulation technology.The criterion of the failure mode of the disc specimen in the split state was theoretically deduced.The influence of structural surface roughness and loading inclination angle on the stress state at the center of the specimen was explored.The results showed that the failure modes of the samples could be divided into three typical modes as matrix failure,structural plane failure and combination failure.The rough structural plane improves the failure strength of the specimen by limiting its lateral deformation,and the degree of improvement weakens continuously with the increase of the inclination angle of the structural plane.As the inclination angle of the structural plane increases,the main type of microcracks in the structural plane changes from shear microcracks to tensile microcracks.This study contributes to a better understanding of macro-and meso-failure characteristics of rock masses with structural planes under a splitting state.
基金Project(2015CB060200)supported by the National Basic Research and Development Program of ChinaProjects(51322403,51274254)supported by the National Natural Science Foundation of China
文摘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.
基金Projects(51879148,51709159,51911530214)supported by the National Natural Science Foundation of ChinaProject(2019GSF111030)supported by Shandong Provincial Key R&D Program of ChinaProject(KT201804)supported by the Project of Special Fund for Science and Technology of Water Resources Department of Guizhou Province,China。
文摘Hydraulic fracturing,as a key technology of deep energy exploitation,accelerates the rapid development of the modern petroleum industry.To study the mechanisms of hydraulic fracture propagation and rock failure mode of the vertical well hydraulic fracturing,the true triaxial hydraulic fracturing test and numerical simulation are carried out,and the influence of the principal stress difference,water injection displacement,perforation angle and natural fracture on fracture propagation is analyzed.The results show that the fracture propagation mode of limestone is mainly divided into two types:the single vertical fracture and the transverse-longitudinal crossed complex fracture.Under high displacement,the fracturing pressure is larger,and the secondary fracture is more likely to occur,while variable displacement loading is more likely to induce fracture network.Meanwhile,the amplitude of acoustic emission(AE)waveform of limestone during fracturing is between 0.01 and 0.02 mV,and the main frequency is maintained in the range of 230−300 kHz.When perforation angleθ=45°,it is easy to produce the T-type fracture that connects with the natural fracture,while X-type cracks are generated whenθ=30°.The results can be used as a reference for further study on the mechanism of limestone hydraulic fracturing.
