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

TLDR

The study introduces an improved relationship for degree‑of‑saturation variation in unsaturated soil that incorporates void‑ratio changes. This relationship is integrated into an elasto‑plastic stress–strain model and validated against extensive laboratory tests on compacted Speswhite kaolin under diverse stress paths, including wetting, loading, unloading, and shearing. The enhanced representation significantly affects numerical coupled flow‑deformation models by altering the suction and thereby the predicted stress–strain behavior.

Abstract

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.