Effective stress in unsaturated soil: a microstructural analysis

When we talk about deformation and failure of a soil, we mean the deformation and failure of the soil skeleton, which, according to the principle of effective stress (Terzaghi, 1936), are governed by the intergranular forces expressed in terms of a continuum quantity called effective stress. From the viewpoint of elasto-plasticity in soil mechanics, the effective stress plays two roles:

Although the principle of effective stress is regarded as one of the most fundamental concepts in soil mechanics, its applicability to unsaturated soils has been debated for a long time (refer to Chapter 3, Fredlund and Rahardjo,...