Effects of wetting-drying cycles on the air permeability of compacted Téguline clay

Due to their low permeability and self-sealing ability, compacted clays are often considered as barrier materials in waste disposal. In most disposal cases these materials are exposed to atmosphere and thus subjected to wetting-drying cycles. As a result, their microstructures might significantly change and sometimes cracks can occur, giving rise to changes in hydro-mechanical properties. It is expected that this microstructure change can be evidenced through changes in air permeability since any growth of micro-cracks can greatly affect the air permeability. In this study, the air permeability evolution of Téguline clay compacted at 12.7% and 16.0% water content during wetting-drying was investigated. The results show that the final water content, void ratio and degree of saturation decreased with the increase of wetting-drying cycles. Cracks occurred in the radial direction on the sample surface rather than in the axial direction after 4-5 wetting-drying cycles. The coefficient of air permeability of the compacted samples is larger than those of the samples subjected to wetting-drying cycles. It also appears that the coefficient of air permeability increases with wetting-drying cycles and the initial water content has insignificant effects on the wetting-drying behaviour and air permeability characteristics. Furthermore, the coefficient of air permeability in the axial direction is larger than the one in the radial direction after the initial 2 wetting-drying cycles, suggesting an anisotropic behaviour with larger shrinkage in the axial direction. These findings show clearly that the effects of wetting-drying cycles on soil microstructure can be effectively investigated through air permeability measurements.