Prediction of effective stress in partially saturated sand-kaolin mixtures

This paper addresses the applicability of the effective stress principle in partially saturated soils by proposing a definition of the effective stress parameter. The definition of the effective stress parameter is based on a model for the soil-water retention relationship (SWCC model) considering the soil saturation as a sum of a term representing the water stored in the bimodal soil-pore system and a term accounting the water adsorbed on the solid surface. The validation of the proposed effective stress parameter is done by conducting conventional triaxial and uniaxial tensile tests on partially saturated samples of artificial compacted sand-kaolin mixtures and by analyzing the results. It is shown that the proposed effective stress parameter is applicable for sandy to non-swelling clayey soils and it can explain the shear strength of the soil in a wide range of suctions. However, the experimental results showed significant difference in measured and predicted tensile strength for the soils with higher clay contents. This discrepancy may be attributed to soil structure effects and to the different processes determining shear strength and tensile strength, indicating the need of further research in this case.