Abstract:

A widely accepted two-parameter theory proposed by Fredlund for unsaturated soils uses the net stress and suction as stress-state variables; it cannot consider the effect of saturation degree or water content on the stress-strain behaviour and strength of unsaturated soils directly. The triaxial test results show that even if the path of net stress and the suction are the same, the stress-strain relation and strength are different due to different saturation degrees. While other conditions are the same, the higher the saturation degree of the specimen, the higher the stress ratio versus strain relation. The latest elastoplastic constitutive model coupling hydraulic and mechanical behaviours could quantitatively reproduce the above behaviours of unsaturated soils.

Key words: unsaturated soil, stress state variable, saturation degree, triaxial test