Locally available expansive soils as a liner material for municipal landfills

Abstract

The bottom liners in the municipal landfill sites are expected to prevent the migration of pollutants (leachate) to the groundwater. Different types of liner materials are being used in the construction of liners of municipal landfills over the world. Compared to the liner materials such as Geosynthetic Clay Liners (GCL) and High Density Polyethythene (HDPE), Compacted Clay Liners (CCL) are more economical, if materials are locally available. Different types of clay have been experimented for their suitability as liner materials in many countries. An expansive soil however, having a high plasticity index can be expected to absorb more volume of water emanating from the leachate and as a result it can withstand longer dry periods before cracks develop. Further, even if cracks do develop during a prolonged dry period, the cracks may self heal with the subsequent exposure to a rainy period as the shrink-swell behavior of expansive soils is reversible. Therefore, in this study, the suitability of a locally available expansive soils in which the major clay mineral is montmorillonite was investigated for use in landfill liners. For this purpose expansive soils obtained from Digana and Moragahakanda areas of Sri Lanka were chosen as candidate soils. The Rowe Cell apparatus was used to measure the hydraulic conductivity of the consolidated soil sample using de-aired water as the permeant liquid. The results showed that for all the test specimens hydraulic conductivity was less than 1x 10-9 m/s conforming to the requirements of maximum hydraulic conductivity recommended for liner materials. Similar tests were performed on expansive soils obtained from Moragahakanda amended by the addition of 5% bentonite (Sodium Bentonite). Addition of bentonite resulted in a decrease of hydraulic conductivity by a significant amount. Therefore, it can be concluded that subjected to the satisfaction of durability criteria the expansive soils of Digana and Moragahakanda are suitable as liner materials and have the potential to be incorporated into a relatively thin liner by amending with bentonite.