Capillary barrier system for landfill capping

Substantial economic and population growth generate a large amount of solid waste in the world. It is common to dispose solid waste by dumping them in sanitary landfills. The most important requirement of a landfill is that it does not pollute or degrade its environment. A method to reduce leachate from a landfill is to reduce rainwater infiltration into a landfill. The use of a cover system for the landfill such as a capillary barrier system (CBS) can reduce rainwater infiltration. A CBS is a man-made two-layer cover system designed as an unsaturated system, harnessing the distinctly different hydraulic properties between a fine-grained layer (sand) and a coarse-grained layer (gravel) of soils. Previous research works indicated that a single layer CBS could be used as slope stabilization purposes against rainfall-induced slope failure in Singapore. In this study, a double layer CBS is proposed to minimize the infiltration of rainwater into the landfill. The recycled materials were used in the double layer CBS to reduce the cost associated with the construction of a cover system in the field and to maintain environmental sustainability. One dimensional seepage analyses were performed to determine the optimum thickness of fine-grained and coarse-grained layers within a double layer CBS and to determine the suitable material combination within the double layer CBS. One dimensional infiltration tests were carried out in the laboratory to verify the results of the numerical analyses. The results from the numerical analyses and infiltration tests indicated that double layer CBS performed better than single layer CBS in minimizing rainwater infiltration.