Rainfall infiltration analysis in unsaturated residual soil slopes

Rainfall-induced slope failure is a common geotechnical problem in the tropics where residual soils are abundant. Residual soils are formed due to the weathering of rocks and lie at the location of the parent rock. They are characterized by the significant variations in the level of weathering and the composition of the weathered product over short distances, Quite often, the ground water table is low during the dry season and these soils are in an unsaturated state. The shear strength of the unsaturated soils is enhanced due to presence ofmatric suction. With the infiltration of rainwater, the matric suction will be depleted for some depth, As the rain progresses the depth of depletion increases. This aspect was studied in this research with an infiltration model. The model was applied initially to a slope formed of homogeneous soil and later to a slope where two layers of significantly different levels of weathering exist. In this study, simulated rainfalls of different intensities and durations representative of tropical climatic conditions were applied to the two different cut slope of southern highway in Sri Lanka. Each Cut slope was analyzed by having different types of weathering profiles. A finite element computer package SEEPIW2007 was used to simulate the infiltration through unsaturated soil