Coupling pore-size distribution and volumetric strains to predict soil-water characteristic curves

The soil-water characteristic curve of soils [SWCC] represents the relationship between suction and degree of saturation. This relationship is fundamental when coupling mechanical and hydraulic behaviors of unsaturated soils. Because the SWCC depends on the void ratio of the soil, it displaces to the left or the right of the suction axis depending on whether the soil experiences compression or expansion. These considerations overcome a serious difficulty when coupling hydro-mechanical behavior since the measured SWCC is only valid for the conditions in which it was determined and not for every deformed state. Hence, when dealing with soils that suffer considerable strains the predicted response of any constitutive model will certainly be inaccurate if the effect of volumetric deformation is not included in the SWCC. In this paper, we present a porous model generated from the initial PSD of the soil that approximately reproduces the initial structure of the material. Based on experimental results, some hypotheses are considered in order to derive a simple equation that defines the new PSD for any deformed state. Model fits well when comparing experimental and predicted SWCCs for any deformed state including large deformations. Because the model is conceived through its PSD, it naturally predicts intermediate wetting-drying paths such as scanning curves which offers an additional feature for constitutive models intended to reproduce cyclic loading.