An elastoplatic framework for coupling hydraulic and mechanical behavior of unsaturated soils

Combining theory of mixture with interfaces (TMI) and the continuum theory of plasticity, a theoretical framework for modeling the elastoplastic constitutive behavior of unsaturated soils is presented. We show that capillary hysteresis, i.e., soil water characteristic curves (SWCCs), is associated with a dissipation mechanism due to the irrecoverable change in volume fraction of water. Within this context, plastic deformation and capillary hysteresis can be consistently simulated in a hierarchical way. Plastic deformation is described by using an intergranular stress tensor that does not require any empirical coefficients and the capillary hysteresis is simulated within the framework of cyclic plasticity. This framework preserves all the advantages of unsaturated soil models based on the effective stress, two stress state variables, and the theory of mixtures. As a first step in developing a comprehensive constitutive model within this framework, a detailed model to simulate SWCCs is presented and compared with experimental data and a good comparison is obtained. A brief description of a novel experimental setup used to rapidly measure the SWCCs is also presented. Finally an isotropic coupled hydraulic–mechanical model is presented and the coupling effects between plastic deformation and capillary hysteresis are investigated.