Seepage through municpal landfill clay liners after cyclic drying and rewetting

Abstract

The sustainability of municipal landfills and quality of water-soil environment is being compromised by the leachate percolation through the bottom sealing liner. The compacted mineral liners, using clays of various plasticity to assure the saturated hydraulic conductivity lower than 1 10 m s, are among the most popular isolations of municipal waste landfills. But high plasticity clays present significant expansivity so they are prone to swelling, shrinkage and resultant cracking. Swelling and shrinkage of compacted clay liners, caused by cyclic drying and watering of substrate, are irreversible and after several cycles may result in a huge increase in the hydraulic conductivity and drastically reduced sealing capabilities of compacted clay liners. This paper presents the assessment of selected substrates’ plasticity influence on the isolating capabilities of the municipal landfill’s bottom liner undergoing cyclic drying and rewetting. The plasticity of tested clay materials was determined and classified by the standard methods. Saturated hydraulic conductivity of the studied clays formed by the standard Proctor method was measured by the laboratory falling head permeameters for compacted soils. Measurements of saturated hydraulic conductivity of the tested substrates after three cycles of drying and rewetting were performed in the standard 100 cm steel cylinders by the falling and constant head laboratory permeameter. Shrinkage of the tested compacted specimens was determined also in the standard 100 cm steel cylinders and classified basing on dimensionless indicator COLE. Determination of water seepage through the tested bottom compacted clay liners was based on the standard form of Darcy law for the saturated conditions of soil medium. The obtained results showed influence of plasticity of clays on decrease in their sealing capabilities after several cycles of drying and rewetting and, by extension, undesirable increase in the seepage volume through the compacted bottom liner.