Modelling volume change behaviour for unsaturated soils in the stress-saturation space

Volume change behaviour of unsaturated soils is usually modelled in terms of stress and suction. This approach is consistent with laboratory tests where suction is a controllable variable. However, it also suffers some limitations. This paper presents an alternative approach for modelling volume change behaviour of unsaturated soils. A new volume change equation is proposed in terms of stress and degree of saturation, to give a better explanation to the non-linear change of soil compressibility under constant suctions. The soil compression index is assumed to be a function of the effective degree of saturation and is interpolated from the known compressibility at the fully saturated state and that at a dry state. The proposed model for volume change is validated against a variety of experimental data in literature.