Abstract
This paper presents results of saturated and unsaturated stability analysis of typical residual slopes subjected to rainfall infiltration corresponds to 50 years rainfall return period. The slope angles considered were 45° and 70°. The saturated stability analyses were carried out for original and critical ground water level commonly considered by practicing engineer. The analyses were conducted using limit equilibrium method. Unsaturated stability analyses used combination of coupled stress–pore-water pressure analysis to evaluate the effect of rainfall infiltration on the deformation and transient pore-water pressure on slope stability. Slope stability analyses were performed at some times during and after rainfall infiltration. Results show that the critical condition for slope made by sandy material was at the end of rainfall while for clayey material was at some specified times after the rainfall ceased. Unsaturated stability analysis on sandy soil gives higher factor of safety because the soil never reached saturation. Transient analysis using unsaturated soil concept could predict more critical condition of delayed failure of slopes made up of clayey soil.
Highlights
Many residual slopes in tropical region with very deep ground water table stand at a steep angle
Factor of Safety (FoS) obtained from slope stability analysis were plotted with respect to time and compared to the factor of safety obtained from conventional analysis considering the original ground water level (GWL) and the assumed critical GWL
Unsaturated slope stability analysis was performed on Slope 1 and Slope 2 in three stages
Summary
Many residual slopes in tropical region with very deep ground water table stand at a steep angle. Heavy downpour may cause raising ground water level (GWL), development of a perched water table and positive porewater pressure in the soil slope This condition will further decrease the shear strength of soil and eventually make the slope increasingly susceptible to failure. Pore-water pressure variation induced by rainfall infiltration is not considered in the current practice using limit equilibrium method. The effect of strength and modulus reduction due to rainfall infiltration could be considered if the concept of unsaturated soil was applied in the analysis [1]. Both effect of stress and pore water pressure should be incorporated in the slope stability analysis.
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