A series of suction-controlled triaxial tests was conducted on Nanyang expansive clay to investigate the effects of dry density and suction on dilatancy and strength.The suction of the soil samples was controlled usin...A series of suction-controlled triaxial tests was conducted on Nanyang expansive clay to investigate the effects of dry density and suction on dilatancy and strength.The suction of the soil samples was controlled using a vapour equilibrium technique,with four suction levels ranging from 3.29 MPa to 198.14 MPa,where water retention is dominated by adsorption.The experimental results show that the tested soil exhibits a brittle failure mode under high suction,significantly distinguishing the hydro-mechanical behaviour of the soil at high suction from that observed at low suction.This brittle failure mode significantly increases the contribution of suction to peak strength compared to residual strength,causes the soil to fail before reaching the critical state,a phenomenon not observed in soils under high suction,and results in dilatancy caused by damage to the soil particle aggregates rather than particle rearrangement.The dilatancy data obtained from the triaxial tests reveal that significant soil dilatancy occurs during shear after reaching peak strength,with the maximum dilatancy angle increasing with suction and decreasing with confining pressure.However,the initial dry density has a negligible impact on the soil's dilatancy under high suction levels.This observation further supports that,for unsaturated soils under high suction levels,dilatancy is attributed to damage to soil particle aggregates rather than the rearrangement of soil particles.展开更多
This study investigated the hydraulic and mechanical behaviors of unsaturated coarse-grained railway embankment fill materials(CREFMs)using a novel unsaturated large-scale triaxial apparatus equipped with the axis tra...This study investigated the hydraulic and mechanical behaviors of unsaturated coarse-grained railway embankment fill materials(CREFMs)using a novel unsaturated large-scale triaxial apparatus equipped with the axis translation technique(ATT).Comprehensive soil-water retention and constant-suction triaxial compression tests were conducted to evaluate the effects of initial void ratio,matric suction,and confining pressure on the properties of CREFMs.Key findings reveal a primary suction range of 0 e100 kPa characterized by hysteresis,which intensifies with decreasing density.Notably,the air entry value and residual suction are influenced by void ratio,with higher void ratios leading to decreased air entry values and residual suctions,underscoring the critical role of void ratio in hydraulic behavior.Additionally,the critical state line(CSL)in the bi-logarithmic space of void ratio and mean effective stress shifts towards higher void ratios with increasing matric suction,significantly affecting dilatancy and critical states.Furthermore,the study demonstrated that the mobilized friction angle and modulus properties depend on confining pressure and matric suction.A novel modified dilatancy equation was proposed,which enhances the predictability of CREFMs'responses under variable loading,particularly at high stress ratios defined by the deviatoric stress over the mean effective stress.This research advances the understanding of CREFMs'performance,especially under fluctuating environmental conditions that alter suction levels.展开更多
A dynamic spherical cavity-expansion penetration model is suggested herein to predict the penetration and perforation of concrete targets struck normally by ogivalnosed projectiles.Shear dilatancy as well as compressi...A dynamic spherical cavity-expansion penetration model is suggested herein to predict the penetration and perforation of concrete targets struck normally by ogivalnosed projectiles.Shear dilatancy as well as compressibility of the material in comminuted region are considered in the paper by introducing a dilatant-kinematic relation.A procedure is first presented to compute the radial stress at the cavity surface and then a numerical method is used to calculate the results of penetration and perforation with friction being taken into account.The influences of various target parameters such as shear strength,bulk modulus,density,Poisson＇s ratio and tensile strength on the depth of penetration are delineated.It is shown that the model predictions are in good agreement with available experimental data.It is also shown that the shear strength plays a dominant role in the target resistance to penetration.展开更多
The dilation angle is the most commonly used parameter to study nonlinear post-peak dilatancy(PPD)behavior and simulate surrounding rock deformation;however,simplified or constant dilatancy models are often used in nu...The dilation angle is the most commonly used parameter to study nonlinear post-peak dilatancy(PPD)behavior and simulate surrounding rock deformation;however,simplified or constant dilatancy models are often used in numerical calculations owing to their simple mathematical forms.This study developed a PPD model for rocks(rock masses)based on the Alejanoe-Alonso(A-A)dilatancy model.The developed model comprehensively reflects the influences of confining pressure(σ_(3))and plastic shear strain(γ^(p)),with the advantages of a simple mathematical form,while requiring fewer parameters and demonstrating a clear physical significance.The overall fitting accuracy of the PPD model for 11 different rocks was found to be higher than that of the A-A model,particularly for Witwatersrand quartzite and jointed granite.The applicability and reliability of the PPD model to jointed granites and different scaled Moura coals were also investigated,and the model was found to be more suitable for the soft and large-scale rocks,e.g.deep rock mass.The PPD model was also successfully applied in studying the mechanical response of a circular tunnel excavated in strain-softening rock mass,and the developed semi-analytical solution was compared and verified with existing analytical solutions.The sensitivities of the rock dilatancy to γ^(p) and σ_(3) showed significant spatial variabilities along the radial direction of the surrounding rock,and the dilation angle did not exhibit a monotonical increasing or decreasing law from the elasticeplastic boundary to the tunnel wall,thereby presenting the σ3-or γ^(p)-dominated differential effects of rock dilatancy.Tunnel deformation parabolically or exponentially increased with increasing in situ stress(buried depth).The developed PPD model is promising to conduct refined numerical and analytical analyses for deep tunneling,which produces extensive plastic deformation and exhibits significant nonlinear post-peak behavior.展开更多
It is important to study the dilatancy property of water-saturated rock for understanding the engineering behavior of loaded rock mass. This study carried out the uniaxial and triaxial compressive experiments on the w...It is important to study the dilatancy property of water-saturated rock for understanding the engineering behavior of loaded rock mass. This study carried out the uniaxial and triaxial compressive experiments on the water-saturated red sandstone, analyzed the influences of confining pressure and pore pressure on dilatancy property of water-saturated rock, and discussed the reasonable basis of the stress of dilatancy onset as a strength design parameter of rock engineering, finally established the prediction model of the stress of dilatancy onset under the impacts of confining pressure and pore pressure. The results show that the strength parameters(the stress of dilatancy onset and peak strength) and deformation parameters(axial strain and circumferential strain) of water-saturated sandstone increase with the confining pressure, and the relations can be fitted with a positive linear function. The cohesion and internal friction angle obtained from the stress of dilatancy onset decrease by 11.57% and 7.33%, respectively, when compared with those obtained from the peak strength. The strength parameters and deformation parameters of water-saturated sandstone decrease basically with the increase of pore pressure, in which the relations between strength parameters or axial strain and pore pressure can be fitted with a negative linear function. However, the relation between the peak circumferential strain and the pore pressure should be characterized by a negative exponential function, and the circumferential strain at dilatancy onset isn't affected by the pore pressure.展开更多
Surrounding rocks of weakly consolidated soft rock roadway show obvious strain softening and dilatancy effects after excavation. A damage coefficient concerning modulus attenuation was defined. Response models of stre...Surrounding rocks of weakly consolidated soft rock roadway show obvious strain softening and dilatancy effects after excavation. A damage coefficient concerning modulus attenuation was defined. Response models of stress and displacement of surrounding rock of soft rock roadway and analytical expressions to calculate plastic zones under different interior pressures and non-uniform original rock stresses were derived based on damage theories and a triple linear elastic-plastic strain softening model. Influence laws of dilatancy gradient on damage development, distributions of stresses and displacement in plastic region were analyzed. Interior pressure conditions to develop plastic region under different origin rock stresses were established and their influences on plastic region distribution were also discussed. The results show that the order of maximum principle stress is exchanged between ~0 and trr with the increase of interior pressure P0, which causes distributions of plastic zone and stress shift. Dilatancy effect which has great influences on the damage propagation and displacements in plastic region has little effect on the size of plastic region and stress responses. The conclusions provide a theoretical basis for a reasonable evaluation of stability and effective supporting of weakly consolidated soft rock roadway.展开更多
Explicit finite difference code was used to calculate the stability factors of shallow tunnels without internal support in limit state. The proposed method was formulated within the nonassociative plasticity. For the ...Explicit finite difference code was used to calculate the stability factors of shallow tunnels without internal support in limit state. The proposed method was formulated within the nonassociative plasticity. For the shallow tunnels in soft clay, without considering the influences of pore water pressure and dilatancy, numerical results were compared with the previously published solutions. From the comparisons, it is found that the present solutions agree well with the previous solutions. The accuracy of the strength reduction technique was demonstrated through the comparisons. The influence of the pore water pressure was discussed. For the shallow tunnels in dilatant cohesive-frictional soils, the dilatant analysis was carried out.展开更多
基金support from the China Scholarship Council(CSC)-University of Technology Sydney joint scholarship and the National Key R&D Program of China(Grant No.2016YFC0800200)is gratefully acknowledged.
文摘A series of suction-controlled triaxial tests was conducted on Nanyang expansive clay to investigate the effects of dry density and suction on dilatancy and strength.The suction of the soil samples was controlled using a vapour equilibrium technique,with four suction levels ranging from 3.29 MPa to 198.14 MPa,where water retention is dominated by adsorption.The experimental results show that the tested soil exhibits a brittle failure mode under high suction,significantly distinguishing the hydro-mechanical behaviour of the soil at high suction from that observed at low suction.This brittle failure mode significantly increases the contribution of suction to peak strength compared to residual strength,causes the soil to fail before reaching the critical state,a phenomenon not observed in soils under high suction,and results in dilatancy caused by damage to the soil particle aggregates rather than particle rearrangement.The dilatancy data obtained from the triaxial tests reveal that significant soil dilatancy occurs during shear after reaching peak strength,with the maximum dilatancy angle increasing with suction and decreasing with confining pressure.However,the initial dry density has a negligible impact on the soil's dilatancy under high suction levels.This observation further supports that,for unsaturated soils under high suction levels,dilatancy is attributed to damage to soil particle aggregates rather than the rearrangement of soil particles.
基金jointly supported by the Science Fund for Distinguished Young Scholars of Hunan Province,China(Grant No.2024JJ2073)the National Natural Science Foundation of China(Grant No.52178443)the Fundamental Research Funds for the Central Universities of Central South University,China(Grant No.2022ZZTS0620)。
文摘This study investigated the hydraulic and mechanical behaviors of unsaturated coarse-grained railway embankment fill materials(CREFMs)using a novel unsaturated large-scale triaxial apparatus equipped with the axis translation technique(ATT).Comprehensive soil-water retention and constant-suction triaxial compression tests were conducted to evaluate the effects of initial void ratio,matric suction,and confining pressure on the properties of CREFMs.Key findings reveal a primary suction range of 0 e100 kPa characterized by hysteresis,which intensifies with decreasing density.Notably,the air entry value and residual suction are influenced by void ratio,with higher void ratios leading to decreased air entry values and residual suctions,underscoring the critical role of void ratio in hydraulic behavior.Additionally,the critical state line(CSL)in the bi-logarithmic space of void ratio and mean effective stress shifts towards higher void ratios with increasing matric suction,significantly affecting dilatancy and critical states.Furthermore,the study demonstrated that the mobilized friction angle and modulus properties depend on confining pressure and matric suction.A novel modified dilatancy equation was proposed,which enhances the predictability of CREFMs'responses under variable loading,particularly at high stress ratios defined by the deviatoric stress over the mean effective stress.This research advances the understanding of CREFMs'performance,especially under fluctuating environmental conditions that alter suction levels.
文摘A dynamic spherical cavity-expansion penetration model is suggested herein to predict the penetration and perforation of concrete targets struck normally by ogivalnosed projectiles.Shear dilatancy as well as compressibility of the material in comminuted region are considered in the paper by introducing a dilatant-kinematic relation.A procedure is first presented to compute the radial stress at the cavity surface and then a numerical method is used to calculate the results of penetration and perforation with friction being taken into account.The influences of various target parameters such as shear strength,bulk modulus,density,Poisson＇s ratio and tensile strength on the depth of penetration are delineated.It is shown that the model predictions are in good agreement with available experimental data.It is also shown that the shear strength plays a dominant role in the target resistance to penetration.
基金funded by a Special Fund for Basic Research on Scientific Instruments of the National Natural Science Foundation of China(Grant No.41827807)the Study on Intelligent Technology for Tunnels Construction of Sichuan-Tibet Railway(Grant No.19-21-1).
文摘The dilation angle is the most commonly used parameter to study nonlinear post-peak dilatancy(PPD)behavior and simulate surrounding rock deformation;however,simplified or constant dilatancy models are often used in numerical calculations owing to their simple mathematical forms.This study developed a PPD model for rocks(rock masses)based on the Alejanoe-Alonso(A-A)dilatancy model.The developed model comprehensively reflects the influences of confining pressure(σ_(3))and plastic shear strain(γ^(p)),with the advantages of a simple mathematical form,while requiring fewer parameters and demonstrating a clear physical significance.The overall fitting accuracy of the PPD model for 11 different rocks was found to be higher than that of the A-A model,particularly for Witwatersrand quartzite and jointed granite.The applicability and reliability of the PPD model to jointed granites and different scaled Moura coals were also investigated,and the model was found to be more suitable for the soft and large-scale rocks,e.g.deep rock mass.The PPD model was also successfully applied in studying the mechanical response of a circular tunnel excavated in strain-softening rock mass,and the developed semi-analytical solution was compared and verified with existing analytical solutions.The sensitivities of the rock dilatancy to γ^(p) and σ_(3) showed significant spatial variabilities along the radial direction of the surrounding rock,and the dilation angle did not exhibit a monotonical increasing or decreasing law from the elasticeplastic boundary to the tunnel wall,thereby presenting the σ3-or γ^(p)-dominated differential effects of rock dilatancy.Tunnel deformation parabolically or exponentially increased with increasing in situ stress(buried depth).The developed PPD model is promising to conduct refined numerical and analytical analyses for deep tunneling,which produces extensive plastic deformation and exhibits significant nonlinear post-peak behavior.
基金supported by the National Natural Science Foundation of China (Nos. 51404266 and 11502229)the National Program on Key Basic Research Project of China (No. 2013CB227900)
文摘It is important to study the dilatancy property of water-saturated rock for understanding the engineering behavior of loaded rock mass. This study carried out the uniaxial and triaxial compressive experiments on the water-saturated red sandstone, analyzed the influences of confining pressure and pore pressure on dilatancy property of water-saturated rock, and discussed the reasonable basis of the stress of dilatancy onset as a strength design parameter of rock engineering, finally established the prediction model of the stress of dilatancy onset under the impacts of confining pressure and pore pressure. The results show that the strength parameters(the stress of dilatancy onset and peak strength) and deformation parameters(axial strain and circumferential strain) of water-saturated sandstone increase with the confining pressure, and the relations can be fitted with a positive linear function. The cohesion and internal friction angle obtained from the stress of dilatancy onset decrease by 11.57% and 7.33%, respectively, when compared with those obtained from the peak strength. The strength parameters and deformation parameters of water-saturated sandstone decrease basically with the increase of pore pressure, in which the relations between strength parameters or axial strain and pore pressure can be fitted with a negative linear function. However, the relation between the peak circumferential strain and the pore pressure should be characterized by a negative exponential function, and the circumferential strain at dilatancy onset isn't affected by the pore pressure.
基金Project(51174128)supported by the National Natural Science Foundation of ChinaProject(20123718110007)supported by the Specialized Research Fund for the Doctoral Program of Higher Education of China
文摘Surrounding rocks of weakly consolidated soft rock roadway show obvious strain softening and dilatancy effects after excavation. A damage coefficient concerning modulus attenuation was defined. Response models of stress and displacement of surrounding rock of soft rock roadway and analytical expressions to calculate plastic zones under different interior pressures and non-uniform original rock stresses were derived based on damage theories and a triple linear elastic-plastic strain softening model. Influence laws of dilatancy gradient on damage development, distributions of stresses and displacement in plastic region were analyzed. Interior pressure conditions to develop plastic region under different origin rock stresses were established and their influences on plastic region distribution were also discussed. The results show that the order of maximum principle stress is exchanged between ~0 and trr with the increase of interior pressure P0, which causes distributions of plastic zone and stress shift. Dilatancy effect which has great influences on the damage propagation and displacements in plastic region has little effect on the size of plastic region and stress responses. The conclusions provide a theoretical basis for a reasonable evaluation of stability and effective supporting of weakly consolidated soft rock roadway.
基金Project(200550) supported by the Foundation for the Author of National Excellent Doctoral Dissertation of ChinaProject (09JJ1008) supported by the Natural Science Foundation of Hunan Province, China
文摘Explicit finite difference code was used to calculate the stability factors of shallow tunnels without internal support in limit state. The proposed method was formulated within the nonassociative plasticity. For the shallow tunnels in soft clay, without considering the influences of pore water pressure and dilatancy, numerical results were compared with the previously published solutions. From the comparisons, it is found that the present solutions agree well with the previous solutions. The accuracy of the strength reduction technique was demonstrated through the comparisons. The influence of the pore water pressure was discussed. For the shallow tunnels in dilatant cohesive-frictional soils, the dilatant analysis was carried out.
