A model for the water retention behavior of deformable soils including capillary hysteresis

Experimental findings on the hysteresis of the soil water retention curve, relating the degree of saturation to the matric suction, have to be superimposed with the aspects due to the soil matrix deformation. In order to set a comprehensive model for the retention behavior, we propose to review the main mechanisms of the capillary hysteresis. The paper also quantifies the effects of mechanical straining on the retention curve on the basis of experimental data. The intrinsic shape of the soil water retention curve is first defined, followed by the empirical 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.