Swelling of compacted clay under osmotic gradients

Abstract

Compacted clay liners in landfills and brine ponds are subject to chemical concentration gradients between the soil water in the clay and the reservoir solution. Soil water is the solution residing in soil pores that is chemically composed of water $(H_2O)$ molecules and dissolved salts molecules (ISSS, 1976). These differences in salt concentration generate an osmotic suction difference: osmotic suction refers to suction arising from the presence of dissolved salts in water (Lu & Likos, 2004). This suction difference is dissipated through the diffusion of salts and flow of H2O molecules (Barbour & Fredlund, 1989). Changes in the dissolved salts concentration of soil water from salt diffusion in response to osmotic suction difference will alter the swell magnitudes of expansive clays, which are strongly influenced by salt concentration (Bolt, 1956; Mesri & Olsen, 1971; Yong & Warkentin, 1975; Mitchell, 1993). Osmotic suction differences between soil water and reservoir solution may thus alter the wetting-induced volume change behaviour of compacted clays used as liners in landfills and brine impoundments.