Advances in modelling hysteretic water retention curve in deformable soils

Experimental findings on the hysteretic nature of the soil water retention curve, relating the degree of saturation to the matric suction, have generally to be superimposed with the aspects due to the deformability of the soil matrix. Indeed, most state-of-the-art models for retention curves only feature one of these two essential features, that is either capillary hysteresis or void ratio dependency. In an effort to set an advanced comprehensive model for the retention curves, it is proposed to review some recent results of the capillary hysteresis and focus on the elasto-plastic analogy in the degree of saturation versus suction relationship. The paper also contributes to quantifying the effects of mechanical straining on the retention curve on the basis of experimental data from the literature besides those obtained by the authors. The intrinsic shape of the soil water retention curve is first defined, followed by the empiric relationship between air entry value and void ratio. The retention sub-model of a complete constitutive model for unsaturated soils is described, the mathematical formulation being based on kinematic hardening and featuring direct coupling with the mechanical stress-strain module. Model capabilities are assessed on complex retention outlines, displaying the added value of the proposed framework for prediction issues.