Laboratory investigation of gas leakage rate through a GM/GCL composite liner due to a circular defect in the geomembrane

The migration of gas through a geomembrane overlying a geosynthetic clay liner (GM/GCL composite) in a landfill cover occurs primarily through defects in the geomembrane. This paper presents the experimental results of an investigation on gas flow through a GM/GCL composite liner where the geomembrane contained a circular defect. It shows that the gas leakage rate is affected by differential gas pressure, moisture content of the GCL, contact conditions, and defect diameter. Moisture content of the GCL was found to be a significant parameter controlling the gas flow rate. This implies that the GCL in a GM/GCL composite should be kept hydrated to high moisture content in order to achieve an effective composite barrier to gas in case a defect occurs in the geomembrane. It is also shown that intimate contact between the geomembrane and the geotextile supported GCL is required to reduce gas leakage rate through a composite system.