A water retention curve and unsaturated hydraulic conductivity model for deformable soils: consideration of the change in pore-size distribution

This paper presents a hysteretic water retention curve (WRC) and unsaturated hydraulic conductivity model for deformable soils based on the change in pore-size distribution (PSD). The PSD plays a decisive role in the water retention behaviour of soils. Although its evolution during deformation is rather complicated, experimental data showed that the overall shapes and distribution characteristics of the PSD function are not significantly altered. Based on these findings, the PSD function at a deformed state is obtained by horizontal shifting and vertical scaling of the corresponding PSD function at a reference state. On this basis, a hysteretic WRC model is formulated to account for the influences of deformation and hysteresis on the variation of saturation, using seven model parameters with clear physical meanings. The proposed model is then incorporated in the Mualem model to predict the unsaturated hydraulic conductivity for deformable soils, using only one additional parameter. A large number of published laboratory tests are used to validate the proposed model, showing that it can reasonably capture important features of retention and permeability properties for deformable soils in most cases under consideration.