Generalised Elasto-Plastic Stress-Strain Relations of a Fully Coupled Hydro-Mechanical Model

Wheeler and co-workers have recently proposed an elasto-plastic framework involving the coupling of hydraulic and mechanical behaviour in unsaturated soils. A characteristic of the model is that it has been formulated in terms of Bishop's stress and modified suction (i.e. suction multiplied by porosity). By using these new stress variables it is possible to predict the influence of the degree of saturation on the stress-strain behaviour. In particular, this new framework is able to represent the coupling between hydraulic and mechanical behaviour, allowing the prediction of influences of changes in the degree of saturation on the stress-strain behaviour and conversely, influences of volumetric strains on the water retention relationship. In this paper a 3D generalization of the stress-strain governing equations of this model is proposed based on concepts of multi-dissipative materials. This is a proper framework as in this model the coupled hydro-mechanical behaviour is described by three elasto-plastic mechanisms