Effect of leachate and freeze-thaw cycles on the hydraulic conductivity of clayey barriers

The effect of freeze-thaw cycles on the hydraulic conductivity (HC) of clayey barriers in water retaining structures and municipal solid waste landfills is a key issue in designing barrier systems in those structures. The effect of freeze-thaw cycles on the hydraulic conductivity of a compacted clayey soil from Nazlou Region of Urmia City and a geosynthetic clay liner (GCL) was investigated. The effect of effective stress on the hydraulic conductivity change of clayey soil in freeze-thaw cycles was studied for water and leachate. The flexible-wall triaxial hydraulic conductivity apparatus was used to measure the HC of specimens subjected to freeze-thaw. During the freezing process, ice lenses grow in soil sample and when they melt, a network of cracks is left causing the increase of HC. Increasing the effective stress reduces the increased hydraulic conductivity due to freeze-thaw. The results show that on the contrary to compacted clayey soil, the application of freeze-thaw cycles does not significantly affect the HC of GCL. Interaction of clayey soil with leachate leads to decrease in thickness of diffuse double layer and thus the hydraulic conductivity of clayey soil increases. Increase in hydraulic conductivity of clayey soil and GCL subjected to freeze-thaw and permeated with leachate is lower than that for water.