Shear strength properties and soil-water characteristic curves of residual soil

The negative pore-water pressure or matric suction in unsaturated soil contributes to the shear strength and consequently the stability of residual soil slopes. Rainfall infiltration and water flow results in the decrease in matric suction, which will reduce the shear strength of the soil and may trigger slope failures. The unsaturated shear strength parameter (ϕb) is an unsaturated shear strength parameter, which indicates the rate of change in shear strength with respect to a change in matric suction. However, ϕb is not a constant value and ϕb value depends on the corresponding matric suctions. SLOPE/W (Geo-Slope International Ltd., 2012) is a commonly used tool for stability analysis. However, it is not capable of incorporating different ϕb values for different matric suctions. This report studies the effect of incorporating the same ϕb value and various ϕb values on the stability of residual soil slope during rainfall by using total cohesion method. Experiments were performed to obtain the saturated coefficient of permeability, soil-water characteristic curve (SWCC), and shear strength of the residual soil. The permeability function and the shear strength parameters were therefore determined and used in the seepage analysis and slope stability analysis. The results of the slope stability analyses showed a significant difference in factor of safety by incorporating the change of ϕb values and without considering the change of ϕb values.Bachelor of Engineering (Civil