Hydro-mechanical double-yield-surface model for unsaturated sand and clay

Abstract

Hydro-mechanical coupling behavior analysis with a sophisticated model for both unsaturated sand and clay is still a challenge. In this study, a hydro-mechanical coupling model with two plastic deformation mechanisms, i.e., loading collapse and shear sliding, for unsaturated soils is formulated using the Bishop’s stress as the stress variable and using the void ratio and the effective degree of saturation as the state variables. An expression for the critical state line related to the effective degree of saturation in the void ratio-soil skeleton stress semilog plane is explicitly implemented, which is combined with a non-associated flow rule for the shear sliding yield surface to guarantee the satisfactory simulation of the dilation or contraction during shear for unsaturated soils including sand and clay. The predictive capability of the model to reproduce the main features of unsaturated soil behavior is analyzed by simulating the triaxial tests on silty sand and kaolin. 使用精细的本构模型来同时分析非饱和砂土和黏土水力耦合特性依旧是一个挑战。提出了一种包含加载湿陷及剪切滑移双重塑性机制的水-力耦合模型。力学模型中选取Bishop应力作为应力变量,采用孔隙比和有效饱和度作为状态变量。模型中给出了孔隙比-平均土骨架应力的半对数坐标系内依赖于有效饱和度的临界状态线的表达式,其与剪切滑动屈服面的非关联流动准则的结合保证了模型可以更合理地预测非饱和土（包括砂土和黏土）的剪胀和剪缩性质。通过模拟粉砂和高岭土的三轴试验,对该模型预测非饱和土主要特征的能力进行了分析。