A fully coupled hydro-mechanical model for the analysis of partially saturated multiphase geo-structures using the bounding surface plasticity

This paper presents a fully coupled plasticity model for the rigorous analysis of fluid flow and solid skeleton deformation in variably saturated porous media. The flow deformation behaviour of unsaturated soils is described through the simultaneous solution of governing partial differential equations, including the equilibrium equation and the continuity equations of pore fluids. The coupling between solid and fluid phases is established based on the effective stress concept with the effective stress parameter as a function of suction. The elasto-plastic behaviour of geomaterials is formulated using the bounding surface theory. The fully coupled flow deformation framework along with the UNSW bounding surface constitutivelaw are implemented into COMSOL Multiphysics commercial software to simulate the results of several laboratory tests conducted on soils with different degrees of saturation under various drainage conditions and loading paths. The close agreement between the numerical solutions and experimental data from the literature indicates the good performance of this new elastic-plastic unsaturated model and emphasises its capability to capture the different characteristic features of response of soils with a variety of saturation degrees and over-consolidation ratios.