ABSTRACT
In this paper, the hypotheses on which the effective stress principle of saturated soils is based and the limitations are first discussed. Some problems on the effective stress of unsaturated soils are then focused on. The formula of average soil skeleton stress that is derived from equilibrium equations of unsaturated soils is provided. Limitations and validity of effective stress principle of unsaturated soil is then discussed. The concept of soil structure is also discussed in this paper and a comprehensive definition of structure of unsaturated soils is formulated.
