Impact of placement and field conditions on hydraulic conductivity and lifetime of liners

The sand-expansive clay liners have a wide application in geoenvironmental and geotechnical projects as hydraulic barriers or cover layers in waste management systems. The flow and mass variations have a significant effect on the hydraulic conductivity of sand-expansive clay liners during their lifetime. This study suggests the use of flooding and/or standing water as a technique to ensure adequate long-term performance. The placement conditions and environmental exposures do have a major effect on the lifetime of liners. The performance of liners is influenced by the size of fluid flow, mass stability, and applied vertical-stresses. This study aimed at investigating the effect of flow and mass variations on the hydraulic conductivity of sand-expansive clay liners during their lifetime. A series of permeability tests were conducted for compacted specimens of sand-expansive clay mixtures with 15 and 20% clay content and sand with 15%-bentonite. The influence of two different vertical stresses (7 and 30 kPa) on the hydraulic conductivity of sand-expansive clay mixture with 20% clay content is monitored and compared over 100 days period, applying a continuous flow of water. The effect of temperature variations and volume-changes were also observed. It was found that the hydraulic conductivity initially measured would not remain stable when subjected to continuous flow for an extended time. The mass loss contributed initially to increasing the hydraulic conductivity until a certain stage where the hydraulic conductivity improves due to soil-structure collapse. The outcome of this work suggests the use of flooding and/or standing water as a technique to ensure adequate long-term performance to accommodate the influence of placement and environmental exposure.