A potential technique to determine the unsaturated soil shear strength parameter

Abstract

The shear strength behavior of unsaturated soils is a complex phenomenon. The major factors that lead to the complex behavior are grain size, natural alteration in status of moisture and associated capillary potential. The need for research is felt to understand the various aspects associated with development of shear strength of unsaturated soils. The research is conducted to obtain the most economical and reliable design solutions. The magnitude of positive pore water pressure developed in saturated soil reduces the shear strength to a great extent. The tensile pore water pressure in the capillary meniscus developed around the soil grain contacts, on the contrary, enhances the factor of safety in the case of unsaturated soil mass. In this research, the shear strength of unsaturated soil is studied for a range of saturation based on the parametric study. The principle of effective stress has proven to be the basis for understanding the shear strength of saturated soil mass and it has provided an explanation for the geotechnical engineering problems. The thesis presents a study on the shear strength of the soil specimen using the direct shear apparatus. The previous research was mainly directed towards evaluation of shear strength under controlled soil suction, by modifying the apparatus. A simple technique is put forward in this research by making use of the conventional direct shear apparatus for testing the unsaturated soil. The suction stress was induced in the soil specimen and the shear strength was evaluated. The soil water characteristic curve has been used in the research to determine the tensile pore water pressure. Hypothesis based on parametric study has been put forward to present a technique to determine the unsaturated soil shear strength parameter in the thesis.