The shear strength parameters for geotechnical designs are obtained mainly from consolidated drained (CD) or consolidated undrained (CU) triaxial tests. However, during construction, the excess pore-air pressure gener...The shear strength parameters for geotechnical designs are obtained mainly from consolidated drained (CD) or consolidated undrained (CU) triaxial tests. However, during construction, the excess pore-air pressure generally dissipates instantaneously while the excess pore-water pressure dissipates with time. This condition needs to be simulated in a constant water content (CW) triaxial test. The study on Yunnan red clay is carried out to investigate the soil-water characteristics and the shear strength characteristics under the constant water content condition. Osmotic technique is used to obtain the soil-water characteristic curve. A series of CW triaxial tests are conducted on statically compacted specimens. The experimental results show that the soil-water characteristic curve has a low air entry value of 7 kPa due to large pores in non-uniform pore size distribution, and a high residual value exceeding 10 MPa. In addition, the initial degree of saturation and net confining stress play an important role in affecting the shear characteristics under the constant water content condition. Finally, a new semi-empirical shear strength model in terms of degree of saturation is proposed and then applied to Yunnan red clay. Simulation result shows that the model is capable of capturing some key features of soils. The model can be used in whole engineering practice range, covering both unsaturated and saturated soils.展开更多
Inherently anisotropic soil fabric has a considerable influence on soil strength. To model this kind of inherent anisotropy, a three-dimensional anisotropic failure criterion was proposed, employing a scalar-valued an...Inherently anisotropic soil fabric has a considerable influence on soil strength. To model this kind of inherent anisotropy, a three-dimensional anisotropic failure criterion was proposed, employing a scalar-valued anisotropic variable and a modified general three- dimensional isotropic failure criterion. The scalar-valued anisotropic variable in all sectors of the deviatoric plane was defined by correlating a normalized stress tensor with a normalized fabric tensor. Detailed comparison between the available experimental data and the corresponding model predictions in the deviatoric plane was conducted. The proposed failure criterion was shown to well predict the failure behavior in all sectors, especially in sector II with the Lode angle ranging between 60° and 120°, where the prediction was almost in accordance with test data. However, it was also observed that the proposed criterion overestimated the strength of dense Santa Monica Beach sand in sector III where the intermediate principal stress ratio b varied from approximately 0.2 to 0.8, and slightly underestimated the strength when b was between approximately 0.8 and 1. The difference between the model predictions and experimental data was due to the occurrence of shear bending, which might reduce the measured strength. Therefore, the proposed anisotropic failure criterion has a strong ability to characterize the failure behavior of various soils and potentially allows a better description of the influence of the loading direction with respect to the soil fabric.展开更多
The red clay in Chenzhou, Hunan province is mostly in unsaturated state. Simply applying the mechanical properties that derived from classic saturated soil mechanics often leads to slope failures in this region. In or...The red clay in Chenzhou, Hunan province is mostly in unsaturated state. Simply applying the mechanical properties that derived from classic saturated soil mechanics often leads to slope failures in this region. In order to study the shear strength characteristic of unsaturated red clay in Chenzhou and to explore a shear strength equation that can be easily applied in engineering practice, a series of triaxial tests of saturated and unsaturated red clay samples were performed using the regular triaxial testing apparatus. The testing results show that the peak strength of red clay drops slightly before the moisture content of 30% but decreases sharply after that. The friction angle of red clay under unsaturated state is basically equal to the effective friction angle under saturated state, while the cohesion of unsaturated red clay is far much bigger than that of saturated one, which indicates that the matric suction makes a great contribution to the cohesion. By fitting the testing results with appropriate curves, the relationships between total strength parameters and with moisture content were obtained. The total increases logarithmically before the moisture content of 35% then decreases linearly, while decreases cubically with increasing moisture content.展开更多
以含砂量较多的花岗岩残积土为研究对象,通过分析其颗粒级配推断这类土具有过渡力学行为的可能性,随后对其进行了等向固结试验与不同应力路径下的三轴剪切试验,结果表明:该残积土为过渡性质土,其力学行为不能通过临界状态理论来描述;不...以含砂量较多的花岗岩残积土为研究对象,通过分析其颗粒级配推断这类土具有过渡力学行为的可能性,随后对其进行了等向固结试验与不同应力路径下的三轴剪切试验,结果表明:该残积土为过渡性质土,其力学行为不能通过临界状态理论来描述;不同初始孔隙比的土体在各向等压固结阶段,在v-lnp′平面上的曲线不能汇集在一起形成唯一的正常固结曲线(Normal Consolidation Line,NCL),剪切过程中同样不存在唯一的临界状态线(Critical State Line,CSL),土体在固结与剪切过程中的应力状态受初始孔隙比影响,且这种影响是不会被过大的固结压力或剪切应力所消除,是一种典型的过渡力学行为;不同初始孔隙比土体在v-lnp′平面上的正常固结曲线与相应临界状态线是相互平行的,且二者间距离固定,与初始孔隙比无关。展开更多
基金Project(51068002) supported by the National Natural Science Foundation of ChinaProject(10-046-14-1) supported by Guangxi Key Laboratory of Geomechanics and Geotechnical Engineering,China
文摘The shear strength parameters for geotechnical designs are obtained mainly from consolidated drained (CD) or consolidated undrained (CU) triaxial tests. However, during construction, the excess pore-air pressure generally dissipates instantaneously while the excess pore-water pressure dissipates with time. This condition needs to be simulated in a constant water content (CW) triaxial test. The study on Yunnan red clay is carried out to investigate the soil-water characteristics and the shear strength characteristics under the constant water content condition. Osmotic technique is used to obtain the soil-water characteristic curve. A series of CW triaxial tests are conducted on statically compacted specimens. The experimental results show that the soil-water characteristic curve has a low air entry value of 7 kPa due to large pores in non-uniform pore size distribution, and a high residual value exceeding 10 MPa. In addition, the initial degree of saturation and net confining stress play an important role in affecting the shear characteristics under the constant water content condition. Finally, a new semi-empirical shear strength model in terms of degree of saturation is proposed and then applied to Yunnan red clay. Simulation result shows that the model is capable of capturing some key features of soils. The model can be used in whole engineering practice range, covering both unsaturated and saturated soils.
基金supported by the National Science Funds for Distinguished Young Scholars of China(Grant No.50825901)the Scientific Innovation Research Scheme for Jiangsu University Graduates(Grant No.CX10B_207Z)
文摘Inherently anisotropic soil fabric has a considerable influence on soil strength. To model this kind of inherent anisotropy, a three-dimensional anisotropic failure criterion was proposed, employing a scalar-valued anisotropic variable and a modified general three- dimensional isotropic failure criterion. The scalar-valued anisotropic variable in all sectors of the deviatoric plane was defined by correlating a normalized stress tensor with a normalized fabric tensor. Detailed comparison between the available experimental data and the corresponding model predictions in the deviatoric plane was conducted. The proposed failure criterion was shown to well predict the failure behavior in all sectors, especially in sector II with the Lode angle ranging between 60° and 120°, where the prediction was almost in accordance with test data. However, it was also observed that the proposed criterion overestimated the strength of dense Santa Monica Beach sand in sector III where the intermediate principal stress ratio b varied from approximately 0.2 to 0.8, and slightly underestimated the strength when b was between approximately 0.8 and 1. The difference between the model predictions and experimental data was due to the occurrence of shear bending, which might reduce the measured strength. Therefore, the proposed anisotropic failure criterion has a strong ability to characterize the failure behavior of various soils and potentially allows a better description of the influence of the loading direction with respect to the soil fabric.
文摘The red clay in Chenzhou, Hunan province is mostly in unsaturated state. Simply applying the mechanical properties that derived from classic saturated soil mechanics often leads to slope failures in this region. In order to study the shear strength characteristic of unsaturated red clay in Chenzhou and to explore a shear strength equation that can be easily applied in engineering practice, a series of triaxial tests of saturated and unsaturated red clay samples were performed using the regular triaxial testing apparatus. The testing results show that the peak strength of red clay drops slightly before the moisture content of 30% but decreases sharply after that. The friction angle of red clay under unsaturated state is basically equal to the effective friction angle under saturated state, while the cohesion of unsaturated red clay is far much bigger than that of saturated one, which indicates that the matric suction makes a great contribution to the cohesion. By fitting the testing results with appropriate curves, the relationships between total strength parameters and with moisture content were obtained. The total increases logarithmically before the moisture content of 35% then decreases linearly, while decreases cubically with increasing moisture content.
文摘以含砂量较多的花岗岩残积土为研究对象,通过分析其颗粒级配推断这类土具有过渡力学行为的可能性,随后对其进行了等向固结试验与不同应力路径下的三轴剪切试验,结果表明:该残积土为过渡性质土,其力学行为不能通过临界状态理论来描述;不同初始孔隙比的土体在各向等压固结阶段,在v-lnp′平面上的曲线不能汇集在一起形成唯一的正常固结曲线(Normal Consolidation Line,NCL),剪切过程中同样不存在唯一的临界状态线(Critical State Line,CSL),土体在固结与剪切过程中的应力状态受初始孔隙比影响,且这种影响是不会被过大的固结压力或剪切应力所消除,是一种典型的过渡力学行为;不同初始孔隙比土体在v-lnp′平面上的正常固结曲线与相应临界状态线是相互平行的,且二者间距离固定,与初始孔隙比无关。
