Modelling the variation of degree of saturation in a deformable unsaturated soil

An improved relationship for the variation of degree of saturation in an unsaturated soil is presented, incorporating the influence of changes of void ratio. When combined with an elasto-plastic stress–strain model, this is able to represent irreversible changes of degree of saturation and changes of degree of saturation caused by shearing. Experimental data from tests on compacted Speswhite kaolin are used to demonstrate the success of the proposed new expression for degree of saturation. The experimental data involve a wide variety of stress paths, including wetting, isotropic loading and unloading under constant suction, constant suction shearing, and constant water content shearing. Improved representation of the variation of degree of saturation has important consequences for numerical modelling of coupled flow-deformation problems, where the expression used for the degree of saturation can influence significantly the suction generated within the soil and hence the predicted stress–strain behaviour.