A General Fully Coupled Elasto-Plastic Constitutive Model for Unsaturated Soils

Abstract

This paper presents a constitutive model able to describe the reversible and irreversible responses typically observed in the mechanical and water retention behaviour of unsaturated soils. The model is an extension to the 3D stress conditions of the original one proposed by Wheeler and co-workers for isotropic stress states. The framework is especially suitable to model the couplings between the mechanical and the water retention behaviour in unsaturated soils, including, for example, the effect of the degree of saturation on the mechanical response and the influence of deformation in the water retention capacity of soils. The proposed mathematical formulation is based on the theory of elasto-plasticity for strain hardening materials and it is suitable for the implementation of the constitutive model into a finite element program. It is assumed that the behaviour of unsaturated soils can be regarded as the consequence of the joint action of several mechanisms that can be individually or simultaneously activated depending on the generalised stress path considered. The performance of the model is studied by comparing model outputs against experimental data for isotropic stress conditions and a satisfactory agreement is achieved. Also the model performance under the stress conditions of the triaxial test is studied for a fictitious shearing stress path.