A New Model for Unsaturated Soil Using Skeleton Stress and Degree of Saturation as State Variables

Abstract

In this paper, based on experimental results a new constitutive model, using skeleton stress and degree of saturation as independent state variables, is proposed for unsaturated soil, in which the influence of the degree of saturation can be properly described. In the model, a very simple moisture characteristics curve considering moisture hysteresis of unsaturated soil is also proposed. The moisture characteristics curve can not only be applied to secondary drying process but also primary drying process originated from slurry soil. The constitutive model is able to describe not only the behavior of unsaturated soil but also saturated soil because the skeleton stress can smoothly shift to effective stress if saturation changes from unsaturated condition to saturated condition. Meanwhile the overconsolidation, one of the main features of soils that are discussed in the models for saturated soils, is also considered together with the degree of saturation. Other mechanical features such as structure of soil and stress-induced anisotropy can be easily incorporated into the proposed model within the framework of the present research. It is known from the simulation that the main features of unsaturated soil in isotropic consolidation test and triaxial compression test under drained and exhausted condition with different confining stress and suction can be qualitatively described.