A hydro-mechanical constitutive model for unsaturated soils over a wide saturation range

Abstract

A hydro-mechanical constitutive model for unsaturated soils is proposed to describe the hydraulic and mechanical behaviour over a wide saturation range. Bishop’s effective stress and the effective degree of saturation are taken as the basic constitutive variables. A simple and novel loading-collapse yield curve is constructed to capture the variation of the yield stress with the hydraulic state over a wide saturation range. A non-orthogonal plastic flow rule is adopted to obtain the direction of the plastic strain increment. A simple water retention model is developed to describe the hydraulic behaviour of unsaturated soils. The proposed constitutive relation is presented through the calculation of the total strain increment and the calculation of the increment of the effective degree of saturation. All material parameters can be determined through conventional laboratory tests. The performance of the proposed model is illustrated through numerical examples of three classical stress paths, i.e., the isotropic compression path with constant suction, the wetting path with constant net stress, and the triaxial shearing path with constant suction and mean net stress. The capability of the proposed model to capture the hydraulic and mechanical behaviour of unsaturated soils is validated by simulating the test results from the literature.