Effect of effective stress on hydraulic conductivity of bentonite–polymer geosynthetic clay liners to coal combustion product leachates

Experiments were conducted to evaluate the hydraulic conductivity of five geosynthetic clay liners (GCLs) permeated with four synthetic coal combustion product (CCP) leachates (ionic strength = 473–4676 mM). One of the GCLs contained conventional sodium bentonite (Na-B), and the other four GCLs contained a bentonite–polymer (B-P) composites with polymer loading ranging from 0.5 to 12.7% (B-P-0.5–B-P-12.7). Hydraulic conductivity tests were conducted at 20 kPa until reaching hydraulic and chemical equilibrium and then the effective confining stress was increased incrementally from 20 to 100, 250 and 500 kPa. The hydraulic conductivity of B-P GCLs with high polymer loading showed a faster decreasing trend than that of Na-B and B-P GCLs with lower polymer loading as the effective confining stress increased. Additionally, the hydraulic conductivity of GCLs permeated with a synthetic CCP leachate with ionic strength of 473 mM decreased significantly as the effective confining stress increased, whereas the GCLs permeated with an aggressive CCP leachate (e.g. ionic strength = 4676 mM) had limited reduction in hydraulic conductivity at elevated effective confining stress.