真三轴条件下非饱和黄土的有效应力屈服特性

Effective stress yielding behavior of unsaturated loess under true triaxial conditions

为了研究非饱和黄土在有效应力空间的屈服特性,利用真三轴仪对非饱和原状黄土进行了不排水等向净应力压缩固结和不同中主应力参数b值的剪切试验,研究了真三轴压缩条件下非饱和黄土的有效应力屈服变化规律。研究结果表明:有效应力比随着中主应力或净围压的增大而减小,中主应力的增大作用对有效球应力的影响大于广义剪应力;由有效应力比-体应变关系曲线确定的剪缩屈服曲线在有效应力空间具有良好的规律性,屈服点的有效屈服应力随着中主应力和初始吸力的增大而增大;π平面上的有效应力屈服强度面和强度破坏面与SMP强度准则稳合较好,有效球应力和初始吸力越大,屈服强度面和强度破坏面越大。提出了真三轴条件下弹性剪应变和塑性剪应变的计算公式,通过分析有效应力与塑性应变关系得出有效应力空间中不同子午平面内的塑性势面呈椭圆形,且随着中主应力的增大,椭圆屈服面增大。

To study yield characteristics of unsaturated loess in the effective stress space,a series of undrained isotropic net stress compression consolidation and shear tests with different intermediate principal stress parameters b is conducted on unsaturated intact loess by using true triaxial apparatus.The effective stress yielding behaviors of unsaturated loess under true triaxial compression conditions are studied.The results show that the effective stress ratio decreases with an increase in intermediate principal stress or net confining pressure,and the effect of intermediate principal stress on effective spherical stress is greater than that of generalized shear stress.The yield curves determined by the effective stress ratio-volume strain curves have good regularity in the effective stress space,the effective yield stress at yield point increases with an increase in intermediate principal stress and initial suction.The effective stress yield strength surfaces and the strength failure surfaces on theπplane are in good agreement with the SMP strength criterion.As the effective spherical stress and initial suction are larger,the yield strength surface and strength failure surface are more larger.The equations of elastic shear strain and plastic shear strain under true triaxial conditions are proposed.By analyzing the relationship between effective stress and plastic strain,it is concluded that the plastic potential surfaces on different meridian planes in the effective stress space are elliptical,and the elliptical yield surface increases with an increase in intermediate principal stress.