Computation of hydraulic conductivity of montmorillonitic clays by diffuse double layer theory

Abstract

Knowledge of hydraulic conductivity of clays is very important in many cases and in waste containment system in particular. Several investigations have been carried out on hydraulic conductivity in the past and it has been brought out that the hydraulic conductivity is strongly influenced by the pore fluid chemistry apart from the soil type and void ratio. Based on the theoretical considerations, the effect of dielectric constant of the pore fluid, valency and concentration of cations in the pore fluid, it is surmised that the hydraulic conductivity is significantly influenced by diffuse double layer thickness, which reduces the pore volume through which flow takes place. A study of Gouy-Chapman diffuse double layer theory show that the diffuse double layer thickness is negligible for non-polar fluid with very low dielectric constant (e.g. CCl4). Considering the thickness of diffuse double layer contributed by CCl4 as zero, the equivalent thickness of diffuse double layer as affected by dielectric constant, valency, concentration, hydrated radius of cation and specific surface has been estimated and presented for montmorillonitic clays. The effective void ratio has been evaluated and a unique relationship between effective void ratio and hydraulic conductivity has been brought out for montmorillonitic clays with different pore medium chemistry. The present study throws more light on the fundamental mechanisms controlling the hydraulic conductivity in clays.