Effects of perched water table on slope stability in unsaturated soils

Instability is an extremely important consideration in the design and construction of man-made slopes and natural slopes. Slope failures and landslides are influenced by geologic topographic and climatic factors. In tropical region, most of the slope failure occurs during severe rainfall. Rain water infiltrates into the slope and reduce the soil matric suction and the strength of the soil. Perched water table may also develops depending on the permeability of the soil layers in the slope and the rate of infiltration. In the paper, effect of perched water table, which occurs after severe rainfall and underlying of impermeable layer were studied. The effects of perched water table on factor of safety of slope were analysed by varying the permeability ratio of soil layers, thickness of impermeable layer, position of impermeable layer, number of impermeable layer and orientation of impermeable layer.