Determination of Fundamental Characteristics of Unsaturated Residual Soils in Sri Lanka

Abstract

The complex behavior and limited studies of unsaturated soil leads to difficulties in implementing effective design procedures, mainly in slope stability. As Sri Lanka is a tropical country mostly consist of residual soil, it experiences drying and wetting conditions. Methods available for slope stability and landslides prevention techniques in Sri Lanka are not cost effective and accurate. As such, in this research study, Soil Water Characteristic Curve (SWCC) was developed for residual soil available in Sri Lanka using tensiometers and which may useful in the slope stability analysis. Disturbed residual soil samples collected from a landslide in Southern expressway near Beliatta area was used for this research study. The Soil Water Characteristic Curve (SWCC) and permeability function were developed for the residual soil by conducting a series of laboratory tests using tensiometers. The continuous drying and wetting paths were developed to represent the natural soil under dry and rainy seasons. Further, shear strength parameters under different moisture contents were determined using a series of direct shear tests. As such, shear strength parameters corresponding to different matric suctions were obtained. Further, SWCC was developed for the residul soil using available empirical methods such as Arya-Paris model. The results obtained depicted that cohesion kept decreasing and friction angle kept constant with the increasing of saturation of soil on wet side and a slight increment on dry side. Further, cohesion and the suction show a non linear relationship. The SWCC obtained through tests and empirical methods were approximately equal for the considered suction range. Permeability results shows a rapid increment when suction reduces.