Effect of wet-dry cycling on swelling and hydraulic conductivity of GCLs

Atterberg limits, free swell, and hydraulic conductivity tests were conduct ed to assess how wet-dry cycling affects the plasticity and swell of benton ite, and the hydraulic conductivity of geosynthetic clay Liners (GCLs) hydr ated with deionized (DI) water (pH 6.5), tap water (pH 6.8), and 0.0125-M C aCl2 solution (pH 6.2). The plasticity of bentonite hydrated with DI water increased during each wetting cycle, whereas the plasticity of bentonite hy drated with tap water and CaCl2 decreased during each wetting cycle. Wet-dr y cycling in DI water and tap water had Little effect on swelling of the be ntonite, even after seven wet-dry cycles. However, swelling decreased drama tically after two wetting cycles with CaCl2 solution. Hydraulic conductivit y of GCL specimens remained low during the first four wetting cycles (simil ar to 1 X 10(-9) cm/s). However, within five to eight cycles, the hydraulic conductivity of all specimens permeated with the 0.0125-M CaCl2 solution i ncreased dramatically, to as high as 7.6 x 10(-6) cm/s. The hydraulic condu ctivity increased because cracks, formed during desiccation. did not fully heal when the bentonite rehydrated. In contrast, a specimen continuously pe rmeated for 10 months with the 0.0125-M CaCl2 solution had low hydraulic co nductivity (similar to 1 x 10(-9) cm/s), even after eight pore volumes of h ow.