Using soil water characteristic curve in computing unsaturated hydraulic conductivity of compacted tropical soil

Abstract

Contaminants flow through compacted soil liners and coversare usually considered under saturated conditions during design stage. Whereas, the compacted soil barriers in reality are neither completely saturated nor completely dry, rather they are in an unsaturated state. Thus, unsaturated flow principles need to be properly simulated to determine the contaminant flow through compacted soil barriers in order to protect groundwater. Soil water characteristic curve (SWCC) which is the relationship between soil suction and water content is the main modeling parameter of unsaturated soil. This paper evaluates the SWCC data of a tropical laterite soil used as a liner material in sanitary landfill. The effect of gradation with respect to fines content on the dry of optimum, optimum and wet of optimum moisture contents on SWCC were investigated. Laboratory tests using pressure plate apparatus were conducted to determine the variation of volumetric water content with soil suction for a pressure range of 1 kPa to 1000 kPa. The experimental SWCC data were fit to the Brooks and Corey parametric equation to compute the unsaturated hydraulic conductivity. Based on the SWCC data, greater air entry suctions were obtained for specimens with higher fines contents when compacted wet of optimum moisture content and the water retention capacity increased with increase in fines content. Using the SWCC, the unsaturated hydraulic conductivities of the soil liner used in simulating leachate migration were computed.