常压至高压下砂土强度、变形特性试验研究

 砂土材料常压至高压下的强度、变形特性是构建砂土模型的首要问题。开展3种粒组砂土8 MPa围压范围内的等向压缩试验以及0.2～6.4 MPa围压范围内的三轴剪切试验，将砂土常压至高压范围内的力学特性进行系统分析，以获得能够将常压至高压范围内的强度、变形特性进行统一描述的力学参数。通过研究发现：(1) 砂土在高压下出现一定量的颗粒破碎，改变了砂土的剪切耗能机制，使得砂土三轴压缩剪切由剪胀软化特征向剪缩硬化特征转变；(2) 砂土材料的三轴压缩剪切峰值应力比受砂土粒径、围压共同影响，M-C强度准则在高压条件下不再适用；而残余应力比则基本不受粒径、围压的影响，是典型的无黏性摩擦型岩土力学参数，应作为砂土基本力学特性指标；(3) 砂土材料在常压至高压范围内的剪切过程中存在较明显的临界状态现象，临界状态曲线与等向压缩曲线形态相同均呈指数衰减型并在高压条件下产生交叉，两者共同构成砂土材料的状态区间能够体现常压至高压范围内的剪胀与剪缩特征。

Experimental study of strength and deformation characteristics of sand under different pressures

The isotropic compression tests and triaxial shear tests were carried out for 3 different groups of sand. The mechanical properties of sand were analyzed in detail. A certain amount of particle breakage occurred under high pressure，which changed the shear energy consumption and led to a transition from shear dilation and softening to shear contraction and hardening. The particle size of sand and the confining pressure affected the peak stress ratio of sand. The classical M-C strength criterion was found to be not applicable anymore under the high pressure condition. However，the strength formula of the residual stress ratio was hardly affected by the particle size and the confining pressure. The residual stress ratio was a typical cohesionless frictional geomaterial property. The sand showed notably critical state phenomenon in the shearing process from common pressure to high pressure. Both the critical state curve and the isotropic compression curve declined exponentially and crossed each other under the high pressure. Two curves together constituted the state interval of sand which reflects the shear dilation and shear contraction.