This study proposes an approach to simulate the effects of initial density on the relative coefficient of permeability for unsaturated soils. The density-dependent permeability function is derived based on (i) an incremental relationship between the degree of saturation and the initial void ratio with various suctions and (ii) the relationship between the permeability function and the soil-water retention curve (SWRC). Only one additional parameter is required in the proposed function, which can be calibrated using a conventional SWRC test. A number of test results in the literature are employed to validate the proposed density-dependent permeability function, and the model predictions indicate good agreement with the experimental data in the literature.

The principle of effective stress is the most fundamental and important principle in soil mechanics. It serves as the foundation of modern soil mechanics. This paper starts with a discussion of effective stress expressions for unsaturated soils. The relationship between the total stress and stress of each phase in unsaturated soils is developed based on three-phase equilibrium equations of a representative element volume (REV). The expression of average soil skeleton stress, defined as effective stress, for unsaturated soils is then derived. This expression is consistent with the effective stress equation in unsaturated soils derived based on deformation work in the energy conservation equation. The general philosophy for the definition of effective stress in unsaturated soils is pointed out, followed by the discussion of some fundamental problems of unsaturated soils, including effective stress, choice of stress state, capillary phenomenon, and so on. The limitations and application scope of the...

This paper presents a new triaxial apparatus for testing soil water retention curves (SWRCs) under different temperatures. The components of this modified apparatus, as well as the special features of each component, were described. The key part of this innovative apparatus was the temperature control system, which was cooperated with a loading system and a suction control system. Different methods of heating were compared and a more effective method, which used a heating element around the pressure chamber, was consequently adopted. Under different temperatures (25, 40, and 60 °C) and different net mean stresses (40, 100, and 200 kPa), typical results from the SWRCs tests for unsaturated silty clay were presented and analyzed. The experimental results show that the volumetric water content reduces with the increasing temperature at constant suction.