Impact of Geomembrane Defect on Leakage Rate of Landfill Composite Liner Under Mechanical–Chemical Coupled Conditions

Hydraulic conductivity tests and numerical simulations were conducted to evaluate the leakage through a geosynthetic clay liner (GCL)–geomembrane composite liner with a geomembrane defect under mechanical–chemical coupled conditions. A circular geomembrane defect with a diameter of 2 to 7 mm was created in the geomembrane to simulate different defect sizes that may be encountered in the field. Hydraulic conductivity tests were conducted on 155-mm-diameter specimens under an average effective stress of 40 or 240 kPa to simulate different layers of waste placed and permeated with the 100 or 250 mM CaCl2 solution to simulate the aggressive waste leachates that could increase the hydraulic conductivity of GCLs. The maximum leakage rate that can be observed in the field was calculated using the equivalent hydraulic conductivity of the composite liner or predicted using finite-element modeling. The results show that the leakage rate of the composite liner with a geomembrane defect was consistently lower than the leakage rate of the GCL alone. The decrease in the size of geomembrane defects, the decrease in leachate concentration, and the increase in effective stress resulted in a decrease in the leakage rate. Nevertheless, the leakage rate of the composite liner was only up to 17× lower than the leakage rate of GCL alone. The composite liner with a geomembrane defect was not able to achieve an equivalent or lower leakage rate than a standard compacted clay liner alone, suggesting that GCLs need to maintain low hydraulic conductivity even with the protection of geomembranes.