Determination of permeability characteristics and SWCC of an unsaturated residual soils in Sri Lanka

Abstract

Sri Lankan residual soils are formed by weathering of the metamorphic parent rock. Failure in slopes made of such residual soils frequently occurs due to excessive rainfall. With the rain water infiltration, soil will gradually get into a saturated state loosing the matric suction. Sometimes perched water table could also develop. Therefore, with the rainfall, slopes that are stable in dry periods may be subjected to failure. Soil Water Characteristic Curves (SWCC) and knowledge of variation of permeability in unsaturated soil are essential to model this behavior and to devise a reliable early warning system which is in most demand in the present day context. This research project focuses on the development of the permeability function of an unsaturated residual soil in Sri Lanka. Permeability function for both wetting and drying phases were investigated. The method is based on continuously drying and wetting the soil sample while continuously monitoring the suction gradient and the change in soil mass.