A novel unified model for volumetric hardening and water retention in unsaturated soils

This paper presents a novel unified model coupling soil volumetric hardening and water retention. The volumetric hardening law is formulated using the effective stress concept and can be applied to various soil types with unified formulations. This law also considers the influence of stress-induced anisotropy, and provides an enhanced prediction of soil response under elevated stress levels and loading–unloading cycles. Furthermore, this law is coupled with a new Soil Water Retention Curve (SWRC) model by considering the dependency of SWRC on the volume change. The new SWRC model captures the hysteretic nature of the water retention, and offers an improved prediction of the hydraulic path for high suction levels. The SWRC model also allows capturing the experimentally observed reduction in the degree of saturation which may occur during the early compression stage under constant suction. With the coupling of the volumetric hardening law and the SWRC model, the unified model is finally developed. The unified model is validated with reasonable accuracy against a wide range of experimental data reported in the literature on clay, silt and sand.