Abstract:

The principle of effective stress is the most important and fundamental principle in soil mechanics, by which soil mechanics has separated from continuum mechanics and become an independent discipline. Traditionally, however, the validity of the effective stress principle remains questionable for unsaturated soils. The historical evolution of the effective stress for unsaturated soils is reviewed firstly based on an expression of the work input into multiphase porous media; and then the formulation of the generalized effective stress for unsaturated soils is put forward. It is shown that neither the single effective stress nor the two-stress state variable approach is sufficient to describe the deformation and strength characteristics of unsaturated soils. By considering the deformation work input of unsaturated soils, the concept of generalized effective stresses that can be used to simulate the behavior of unsaturated soils is proposed. The proposed approach is fundamental and theoretically sound, paving a solid way to simulate the fundamental behavior and constitutive relation of unsaturated soils.

Key words: unsaturated soil, effective stress, theory of multiphase porous media, deformation work