On the mechanics of partially saturated soils

This paper discusses a rule of decomposition of stresses in saturated soils based on average stress measures in the constituents. On the basis of this decomposition a mathematical framework for describing the mechanical response of partially saturated soils under undrained conditions is proposed. The formulation is derived by treating partially saturated soil as a three phase medium. The liquid (water) and gas (air) phases are assumed to be separated by curved boundaries across which discontinuities in pressure exist due to the surface tension of the liquid. The formulation is restricted to the case when air is entrapped within the liquid phase which is assumed to be continuous. The framework incorporates the average pore size as an independent parameter which governs the evolution of suction pressures in the soil.