The Effect of Long-Term Permeation of Inorganic Salts on the Geotechnical Characteristics of Bentonite-Amended Clay Liners

Bentonite-amended clay liners in engineered landfills are designed to prevent groundwater contamination from landfill leachate. Although numerous studies have examined the shortterm effect of inorganic salts present in the landfill leachate on geotechnical properties of the bentonite-amended clay liners, studies on their long-term effects remain limited. Therefore, this study evaluated the long-term effects of CaCl₂ and NaCl, salts commonly found in landfill leachate, on the plasticity, swelling, compressibility, and hydraulic conductivity of clayey soil amended with 10% and 20% bentonite. These samples were immersed in 1M solutions of CaCl2 and NaCl for 180 days to investigate their long-term effects. In contrast to the results obtained when water was the pore fluid, the liquid limit, plastic limit, free swell index, and free swell of bentonite-amended soils decreased in the presence of CaCl2, MgCl2, and NaCl solutions. Samples immersed in salt solutions showed significantly lower liquid and plastic limits than fresh samples prepared with the same salt solutions. The hydraulic conductivity of all samples exposed to CaCl2 and NaCl decreased with effective stress and reached values less than 1 × 10⁻⁹ m.s-1. The addition of more bentonite did not significantly improve hydraulic conductivity when exposed to different salt solutions in the long term. In conclusion, samples with higher bentonite content are more susceptible to attack by inorganic salts over the long term.