Combined influence of subsoil water content and mass per unit area on cation exchange behavior of geosynthetic clay liners

Abstract

Hydration tests were performed on geosynthetic clay liners (GCL) to examine the influence of subsoil water content (wsubsoil) and mass per unit area (MPUA) on the cation exchange occurred during hydration. Increase in the wsubsoil increased the final water content of GCL (wfinal). At MPUA of 4.0 kg/m2, wfinal increased from 70 to 109%. Such increase was less pronounced when MPUA was considered. Also, an inverse relation between MPUA and wfinal existed where wfinal increased as the MPUA decreased. The greatest wfinal was determined when wsubsoil was ∼17% and MPUA of GCL was ∼3.0 kg/m2 (112%). The exchange reaction was the most favorable when wsubsoil was ∼8% and MPUA of GCL was ∼3.0 kg/m2 (mole fractions of monovalent cations, XM, decreased from 0.81 to 0.65) and the least favorable when wsubsoil was ∼17% and MPUA of GCL was ∼3.0 kg/m2 (XM decreased from 0.81 to 0.80). Combined influence of MPUA and wsubsoil showed that although cation exchange depends on both factors, wsubsoil had significant role in this reaction more than MPUA. The findings of cation exchange analyses were supported with swell index tests. The hydrated GCLs had lower swell indices than the virgin GCL (17.5–19.0 mL/2g vs. 21.5 mL/2g), indicating cation exchange.