The redistribution of three-dimensional(3D)geostress during underground tunnel excavation can easily induce to shear failure along rockmass structural plane,potentially resulting in engineering disasters.However,the c...The redistribution of three-dimensional(3D)geostress during underground tunnel excavation can easily induce to shear failure along rockmass structural plane,potentially resulting in engineering disasters.However,the current understanding of rockmass shear behavior is mainly based on shear tests under2D stress without lateral stress,the shear fracture under 3D stress is unclear,and the relevant 3D shear fracture theory research is deficient.Therefore,this study conducted true triaxial cyclic loading and unloading shear tests on intact and bedded limestone under different normal stress σ_(n) and lateral stressσ_(p)to investigate the shear strength,deformation,and failure characteristics.The results indicate that under differentσ_(n)and σ_(p),the stress–strain hysteresis loop area gradually increases from nearly zero in the pre-peak stage,becomes most significant in the post-peak stage,and then becomes very small in the residual stage as the number of shear test cycles increases.The shear peak strength and failure surface roughness almost linearly increase with the increase inσ_(n),while they first increase and then gradually decrease asσ_(p)increases,with the maximum increases of 12.9%for strength and 15.1%for roughness.The shear residual strength almost linearly increases withσ_(n),but shows no significant change withσ_(p).Based on the acoustic emission characteristic parameters during the test process,the shear fracture process and microscopic failure mechanism were analyzed.As the shear stressτincreases,the acoustic emission activity,main frequency,and amplitude gradually increase,showing a significant rise during the cycle near the peak strength,while remaining almost unchanged in the residual stage.The true triaxial shear fracture process presents tensile-shear mixture failure characteristics dominated by microscopic tensile failure.Based on the test results,a 3D shear strength criterion considering the lateral stress effect was proposed,and the determination methods and evolution of the shear modulus G,cohesion c_(jp),friction angleφ_(jp),and dilation angleψjpduring rockmass shear fracture process were studied.Under differentσ_(n)andσ_(p),G first rapidly decreases and then tends to stabilize;cjp,φ_(jp),andψjpfirst increase rapidly to the maximum value,then decrease slowly,and finally remain basically unchanged.A 3D shear mechanics model considering the effects of lateral stress and shear parameter degradation was further established,and a corresponding numerical calculation program was developed based on3D discrete element software.The proposed model effectively simulates the shear failure evolution process of rockmass under true triaxial shear test,and is further applied to successfully reveal the failure characteristics of surrounding rocks with structural planes under different combinations of tunnel axis and geostress direction.展开更多
In order to study the failure of surrounding rock under high in situ stress in deep underground engineering projects, disturbed by excavation unloading, we carried out triaxial unloading experiments using thickwalled ...In order to study the failure of surrounding rock under high in situ stress in deep underground engineering projects, disturbed by excavation unloading, we carried out triaxial unloading experiments using thickwalled cylinder specimens on a TATW-2000 rock servo-controlled triaxial testing machine in a laboratory. The specimens were made of limestone material, taken from Tongshan county, Xuzhou city, Jiangsu province, China. In our experiments, rock deformation and failure behavior was studied through loading and unloading of inner hole pressure of thick-walled cylinder specimens. At first, the axial stress, confining pressure and inner pressure were increased simultaneously to a specified designed state of stress. Then, keeping the axial stress and confining pressure stable, the pressure on the inner hole was decreased until the specimen was fractured. When the inner pressure was released completely but the specimen did not fracture, the confining pressure was decreased subsequently until complete failure occurred. Our experimental results suggest that traces of major circular ringlike fractures with a number of radial cracks often appear in thick cylinder walls. This type of ringlike failure phenomenon, similar to intermittent zonal fracturing characteristics of deep exploitation, has, so far, not been published. Our experimental results show that rock deformation and failure behavior of thick-walled limestone cylinders vary under different stress paths between loading and unloading. Tensile failure and orderly failure surfaces occur under unloading conditions while irregular damaged rock blocks are produced during loading failure. This type of triaxial unloading experiment provides for new research methodology and approach for thorough investigations on intermittent zonal fracturing in deep underground excavations.展开更多
Mechanical excavation,blasting,adjacent rockburst and fracture slip that occur during mining excavation impose dynamic loads on the rock mass,leading to further fracture of damaged surrounding rock in three-dimensiona...Mechanical excavation,blasting,adjacent rockburst and fracture slip that occur during mining excavation impose dynamic loads on the rock mass,leading to further fracture of damaged surrounding rock in three-dimensional high-stress and even causing disasters.Therefore,a novel complex true triaxial static-dynamic combined loading method reflecting underground excavation damage and then frequent intermittent disturbance failure is proposed.True triaxial static compression and intermittent disturbance tests are carried out on monzogabbro.The effects of intermediate principal stress and amplitude on the strength characteristics,deformation characteristics,failure characteristics,and precursors of monzogabbro are analyzed,intermediate principal stress and amplitude increase monzogabbro strength and tensile fracture mechanism.Rapid increases in microseismic parameters during rock loading can be precursors for intermittent rock disturbance.Based on the experimental result,the new damage fractional elements and method with considering crack initiation stress and crack unstable stress as initiation and acceleration condition of intermittent disturbance irreversible deformation are proposed.A novel three-dimensional disturbance fractional deterioration model considering the intermediate principal stress effect and intermittent disturbance damage effect is established,and the model predicted results align well with the experimental results.The sensitivity of stress states and model parameters is further explored,and the intermittent disturbance behaviors at different f are predicted.This study provides valuable theoretical bases for the stability analysis of deep mining engineering under dynamic loads.展开更多
Applying MTS rock stiffness test machine, tests under triaxial condition were carried out for rockmass under loading and unloading. By measuring and analyzing such mechanical properties as stress, strain, elastic modu...Applying MTS rock stiffness test machine, tests under triaxial condition were carried out for rockmass under loading and unloading. By measuring and analyzing such mechanical properties as stress, strain, elastic modulus, Poisson ratio and elastic wave velocity during the whole test process, the differences of mechanical characteristics under loading and unloading conditions were revealed, to provide some useful references for excavation.展开更多
The RMB-150B rock mechanics test system was employed to obtain the complete stress-strain test curves under confining pressures of 0-30MPa for marble samples from Ya'an ,Sichuan province. On the basis of former st...The RMB-150B rock mechanics test system was employed to obtain the complete stress-strain test curves under confining pressures of 0-30MPa for marble samples from Ya'an ,Sichuan province. On the basis of former study and the convention triaxial pressure test results ,the complete procedures curves which described the relationships between yielding strength、 peak strength、 residual strength and confining pressure was obtained. Taking the strain softening of rock into account, the bilinear elastic-linear softening-residual perfect plasticity four-linear model was put forward in this paper on the basis of the test results and theory of plasticity. This model was adopted to describe the behaviors of marble in different phases under triaxial compression with the constitutive equation of strain softening phase as focus. The results indicated that the theoretic model fitted in well with the test results.展开更多
The in situ shear test and in-lab triaxial shear test on compacted rockfill of Fuling safety embankment were carried out and their advantages and disadvantages were compared. The discreteness of cohesive force C and i...The in situ shear test and in-lab triaxial shear test on compacted rockfill of Fuling safety embankment were carried out and their advantages and disadvantages were compared. The discreteness of cohesive force C and internal frictional angle by in situ shear test is much severer than that by in-lab triaxial shear test. The consolidation of in-lab triaxial shear test is bigger than actual consolidation in rockfill engineerings, so the confining pressure should be reduced to a low level in-lab triaxial shear test.展开更多
The far-field microdynamic disturbance caused by the excavation of deep mineral resources and underground engineering can induce surrounding rock damage in high-stress conditions and even lead to disasters.However,the...The far-field microdynamic disturbance caused by the excavation of deep mineral resources and underground engineering can induce surrounding rock damage in high-stress conditions and even lead to disasters.However,the mechanical properties and damage/fracture evolution mechanisms of deep rock induced by microdynamic disturbance under three-dimensional stress states are unclear.Therefore,a true triaxial multilevel disturbance test method is proposed,which can completely simulate natural geostress,excavation stress redistribution(such as stress unloading,concentration and rotation),and subsequently the microdynamic disturbance triggering damaged rock failure.Based on a dynamic true triaxial test platform,true triaxial microdynamic disturbance tests under different frequency and amplitudes were carried out on monzogabbro.The results show that increasing amplitude or decreasing frequency diminishes the failure strength of monzogabbro.Deformation modulus gradually decreases during disturbance failure.As frequency and amplitude increase,the degradation rate of deformation modulus decreases slightly,disturbance dissipated energy increases significantly,and disturbance deformation anisotropy strengthens obviously.A damage model has been proposed to quantitatively characterize the disturbance-induced damage evolution at different frequency and amplitude under true triaxial stress.Before disturbance failure,the micro-tensile crack mechanism is dominant,and the micro-shear crack mechanism increases significantly at failure.With the increase of amplitude and frequency,the micro-shear crack mechanism increases.When approaching disturbance failure,the acoustic emission fractal dimension changes from a stable value to local large oscillation,and finally increases sharply to a high value at failure.Finally,the disturbance-induced failure mechanism of surrounding rock in deep engineering is clearly elucidated.展开更多
三轴试验离散元模拟是探究砂土等岩土材料变形破坏机制的一种重要手段,合理地模拟侧向边界是三轴试验离散元模拟的一个重要环节。基于有限差分法(finite difference method,简称FDM)-离散元法(discrete element method,简称DEM)FDM-DEM...三轴试验离散元模拟是探究砂土等岩土材料变形破坏机制的一种重要手段,合理地模拟侧向边界是三轴试验离散元模拟的一个重要环节。基于有限差分法(finite difference method,简称FDM)-离散元法(discrete element method,简称DEM)FDM-DEM耦合开展了柔性侧向边界条件下砂土三轴固结排水和不排水试验的数值模拟,并与相应的刚性侧向边界三轴数值试验进行了对比分析。结果表明:相比刚性侧向边界,基于FDM-DEM耦合的柔性侧向边界三轴试验能更好地再现室内砂土三轴试样的宏观力学响应和微观颗粒运动学特征;对于所模拟的砂土三轴固结排水试验,柔性侧向边界试样峰值强度后的应变软化和剪胀性明显弱于刚性侧向边界试样;对于所模拟的砂土三轴固结不排水试验,当轴向应变较大时,柔性侧向边界试样的偏应力小于刚性侧向边界试样,且产生绝对值较小的负孔压;三轴固结不排水试验中,当轴向应变较大时,柔性侧向边界对试样的约束和支撑作用弱于刚性侧向边界,其力链的稳定性较低,力链屈曲数较多,剪切带形成较早,故其各向异性和偏应力均较低。展开更多
基金the National Natural Science Foundation of China(Nos.52469019,52109119,and 52274145)the Chinese Postdoctoral Science Fund Project(No.2022M723408)+1 种基金the Major Project of Guangxi Science and Technology(No.AA23023016)the Technology Project of China Power Engineering Consulting Group Co.,Ltd.(No.DG2-T01-2023)。
文摘The redistribution of three-dimensional(3D)geostress during underground tunnel excavation can easily induce to shear failure along rockmass structural plane,potentially resulting in engineering disasters.However,the current understanding of rockmass shear behavior is mainly based on shear tests under2D stress without lateral stress,the shear fracture under 3D stress is unclear,and the relevant 3D shear fracture theory research is deficient.Therefore,this study conducted true triaxial cyclic loading and unloading shear tests on intact and bedded limestone under different normal stress σ_(n) and lateral stressσ_(p)to investigate the shear strength,deformation,and failure characteristics.The results indicate that under differentσ_(n)and σ_(p),the stress–strain hysteresis loop area gradually increases from nearly zero in the pre-peak stage,becomes most significant in the post-peak stage,and then becomes very small in the residual stage as the number of shear test cycles increases.The shear peak strength and failure surface roughness almost linearly increase with the increase inσ_(n),while they first increase and then gradually decrease asσ_(p)increases,with the maximum increases of 12.9%for strength and 15.1%for roughness.The shear residual strength almost linearly increases withσ_(n),but shows no significant change withσ_(p).Based on the acoustic emission characteristic parameters during the test process,the shear fracture process and microscopic failure mechanism were analyzed.As the shear stressτincreases,the acoustic emission activity,main frequency,and amplitude gradually increase,showing a significant rise during the cycle near the peak strength,while remaining almost unchanged in the residual stage.The true triaxial shear fracture process presents tensile-shear mixture failure characteristics dominated by microscopic tensile failure.Based on the test results,a 3D shear strength criterion considering the lateral stress effect was proposed,and the determination methods and evolution of the shear modulus G,cohesion c_(jp),friction angleφ_(jp),and dilation angleψjpduring rockmass shear fracture process were studied.Under differentσ_(n)andσ_(p),G first rapidly decreases and then tends to stabilize;cjp,φ_(jp),andψjpfirst increase rapidly to the maximum value,then decrease slowly,and finally remain basically unchanged.A 3D shear mechanics model considering the effects of lateral stress and shear parameter degradation was further established,and a corresponding numerical calculation program was developed based on3D discrete element software.The proposed model effectively simulates the shear failure evolution process of rockmass under true triaxial shear test,and is further applied to successfully reveal the failure characteristics of surrounding rocks with structural planes under different combinations of tunnel axis and geostress direction.
基金supported by the National Natural Science Foundation of China (Nos.50804046, 50490273 and 50774082)the Scientific Research Fund for Youths of CUMT (No. 0B080240)
文摘In order to study the failure of surrounding rock under high in situ stress in deep underground engineering projects, disturbed by excavation unloading, we carried out triaxial unloading experiments using thickwalled cylinder specimens on a TATW-2000 rock servo-controlled triaxial testing machine in a laboratory. The specimens were made of limestone material, taken from Tongshan county, Xuzhou city, Jiangsu province, China. In our experiments, rock deformation and failure behavior was studied through loading and unloading of inner hole pressure of thick-walled cylinder specimens. At first, the axial stress, confining pressure and inner pressure were increased simultaneously to a specified designed state of stress. Then, keeping the axial stress and confining pressure stable, the pressure on the inner hole was decreased until the specimen was fractured. When the inner pressure was released completely but the specimen did not fracture, the confining pressure was decreased subsequently until complete failure occurred. Our experimental results suggest that traces of major circular ringlike fractures with a number of radial cracks often appear in thick cylinder walls. This type of ringlike failure phenomenon, similar to intermittent zonal fracturing characteristics of deep exploitation, has, so far, not been published. Our experimental results show that rock deformation and failure behavior of thick-walled limestone cylinders vary under different stress paths between loading and unloading. Tensile failure and orderly failure surfaces occur under unloading conditions while irregular damaged rock blocks are produced during loading failure. This type of triaxial unloading experiment provides for new research methodology and approach for thorough investigations on intermittent zonal fracturing in deep underground excavations.
基金the financial support from the National Natural Science Foundation of China(No.52109119)the Guangxi Natural Science Foundation(No.2021GXNSFBA075030)+2 种基金the Guangxi Science and Technology Project(No.Guike AD20325002)the Chinese Postdoctoral Science Fund Project(No.2022 M723408)the Open Research Fund of State Key Laboratory of Simulation and Regulation of Water Cycle in River Basin(China Institute of Water Resources and Hydropower Research)(No.IWHR-SKL-202202).
文摘Mechanical excavation,blasting,adjacent rockburst and fracture slip that occur during mining excavation impose dynamic loads on the rock mass,leading to further fracture of damaged surrounding rock in three-dimensional high-stress and even causing disasters.Therefore,a novel complex true triaxial static-dynamic combined loading method reflecting underground excavation damage and then frequent intermittent disturbance failure is proposed.True triaxial static compression and intermittent disturbance tests are carried out on monzogabbro.The effects of intermediate principal stress and amplitude on the strength characteristics,deformation characteristics,failure characteristics,and precursors of monzogabbro are analyzed,intermediate principal stress and amplitude increase monzogabbro strength and tensile fracture mechanism.Rapid increases in microseismic parameters during rock loading can be precursors for intermittent rock disturbance.Based on the experimental result,the new damage fractional elements and method with considering crack initiation stress and crack unstable stress as initiation and acceleration condition of intermittent disturbance irreversible deformation are proposed.A novel three-dimensional disturbance fractional deterioration model considering the intermediate principal stress effect and intermittent disturbance damage effect is established,and the model predicted results align well with the experimental results.The sensitivity of stress states and model parameters is further explored,and the intermittent disturbance behaviors at different f are predicted.This study provides valuable theoretical bases for the stability analysis of deep mining engineering under dynamic loads.
文摘Applying MTS rock stiffness test machine, tests under triaxial condition were carried out for rockmass under loading and unloading. By measuring and analyzing such mechanical properties as stress, strain, elastic modulus, Poisson ratio and elastic wave velocity during the whole test process, the differences of mechanical characteristics under loading and unloading conditions were revealed, to provide some useful references for excavation.
文摘The RMB-150B rock mechanics test system was employed to obtain the complete stress-strain test curves under confining pressures of 0-30MPa for marble samples from Ya'an ,Sichuan province. On the basis of former study and the convention triaxial pressure test results ,the complete procedures curves which described the relationships between yielding strength、 peak strength、 residual strength and confining pressure was obtained. Taking the strain softening of rock into account, the bilinear elastic-linear softening-residual perfect plasticity four-linear model was put forward in this paper on the basis of the test results and theory of plasticity. This model was adopted to describe the behaviors of marble in different phases under triaxial compression with the constitutive equation of strain softening phase as focus. The results indicated that the theoretic model fitted in well with the test results.
基金SupportedbyChongqingScienceandTechnologyCommittee (No .2 0 0 1 74 2 9)andWesternCommunicationsProjectofMinistryofCommunications
文摘The in situ shear test and in-lab triaxial shear test on compacted rockfill of Fuling safety embankment were carried out and their advantages and disadvantages were compared. The discreteness of cohesive force C and internal frictional angle by in situ shear test is much severer than that by in-lab triaxial shear test. The consolidation of in-lab triaxial shear test is bigger than actual consolidation in rockfill engineerings, so the confining pressure should be reduced to a low level in-lab triaxial shear test.
基金the financial support from the National Natural Science Foundation of China(No.52109119)the Guangxi Natural Science Foundation(No.2021GXNSFBA075030)+2 种基金the Guangxi Science and Technology Project(No.Guike AD20325002)the Chinese Postdoctoral Science Fund Project(No.2022M723408)the Open Research Fund of State Key Laboratory of Simulation and Regulation of Water Cycle in River Basin(China Institute of Water Resources and Hydropower Research)(No.IWHR-SKL-202202)。
文摘The far-field microdynamic disturbance caused by the excavation of deep mineral resources and underground engineering can induce surrounding rock damage in high-stress conditions and even lead to disasters.However,the mechanical properties and damage/fracture evolution mechanisms of deep rock induced by microdynamic disturbance under three-dimensional stress states are unclear.Therefore,a true triaxial multilevel disturbance test method is proposed,which can completely simulate natural geostress,excavation stress redistribution(such as stress unloading,concentration and rotation),and subsequently the microdynamic disturbance triggering damaged rock failure.Based on a dynamic true triaxial test platform,true triaxial microdynamic disturbance tests under different frequency and amplitudes were carried out on monzogabbro.The results show that increasing amplitude or decreasing frequency diminishes the failure strength of monzogabbro.Deformation modulus gradually decreases during disturbance failure.As frequency and amplitude increase,the degradation rate of deformation modulus decreases slightly,disturbance dissipated energy increases significantly,and disturbance deformation anisotropy strengthens obviously.A damage model has been proposed to quantitatively characterize the disturbance-induced damage evolution at different frequency and amplitude under true triaxial stress.Before disturbance failure,the micro-tensile crack mechanism is dominant,and the micro-shear crack mechanism increases significantly at failure.With the increase of amplitude and frequency,the micro-shear crack mechanism increases.When approaching disturbance failure,the acoustic emission fractal dimension changes from a stable value to local large oscillation,and finally increases sharply to a high value at failure.Finally,the disturbance-induced failure mechanism of surrounding rock in deep engineering is clearly elucidated.
文摘三轴试验离散元模拟是探究砂土等岩土材料变形破坏机制的一种重要手段,合理地模拟侧向边界是三轴试验离散元模拟的一个重要环节。基于有限差分法(finite difference method,简称FDM)-离散元法(discrete element method,简称DEM)FDM-DEM耦合开展了柔性侧向边界条件下砂土三轴固结排水和不排水试验的数值模拟,并与相应的刚性侧向边界三轴数值试验进行了对比分析。结果表明:相比刚性侧向边界,基于FDM-DEM耦合的柔性侧向边界三轴试验能更好地再现室内砂土三轴试样的宏观力学响应和微观颗粒运动学特征;对于所模拟的砂土三轴固结排水试验,柔性侧向边界试样峰值强度后的应变软化和剪胀性明显弱于刚性侧向边界试样;对于所模拟的砂土三轴固结不排水试验,当轴向应变较大时,柔性侧向边界试样的偏应力小于刚性侧向边界试样,且产生绝对值较小的负孔压;三轴固结不排水试验中,当轴向应变较大时,柔性侧向边界对试样的约束和支撑作用弱于刚性侧向边界,其力链的稳定性较低,力链屈曲数较多,剪切带形成较早,故其各向异性和偏应力均较低。
