Experimental investigations were carried out to evaluate the hydraulic performance of Compacted Clay Liners (CCLs) in landfills before waste placement and after waste placement. Results exhibited positive correlation between CCLs’ hydraulic conductivity and plasticity indices when CCLs exposed to daily thermal or wet-dry cycles. Overlaying the CCL with a layer of geomembrane minimized the effects of daily thermal and wet-dry cycles. After waste placement, the hydraulic conductivity for CCL specimens increased by two to three times their initial values when exposed to 55℃ for 75 days. Initial
increase in hydraulic conductivities for all CCL specimens occurred when the permeant was changed from tap water to leachate. However, as the leachate exposure time increased, hydraulic conductivity readings decreased to as low as one order of magnitude after 75 days of leachate permeation at room temperature. The rate of hydraulic conductivity reduction due to leachate permeation was slower at higher temperatures.