Parameters affecting the permeability of bentonite-granular soil mixtures

Abstract

Clay is the natural material which is very effective when used as a liner for waste disposal because of its extremely low permeability. As the clay is used to prevent the leakage of hazardous wastes by minimizing the flow of liquids through it, its most significant feature in this scope is its permeability. It is well known that addition of clay in high permeable soils decreases the permeability of final mixture. In this study, parameters affecting the permeability of bentonite-ganular soil mixtures have been investigated. Tests have been conducted on different aggregate compositions in order to determine the particle size distribution providing minimum void ratio. Series of hydraulic conductivity tests have been conducted on two different bentonite–aggregate compositions. For enhancing hydraulic conductivity performance of bentonite-aggregate mixtures, a water soluble polymer, namely Shore Pac was added and effects of polymer on permeability were investigated. Test results showed that addition of small amount of polymer extremely decreased the permeability of bentonite-granular soil mixtures. It is noted in the literature that there is an inverse relationship between viscosity of permeant and hydraulic conductivity. Viscosity determination tests have been conducted to determine effects of polymer on viscosity. Tests revealed that viscosity of polymer-water solution dramatically increased with the increase in polymer amount. Changes in viscosity and hydraulic conductivity values due to polymer addition were compared and it was concluded that reduction in hydraulic conductivity mainly caused by the increase in viscosity.