Gas transmissivity at the interface of a geomembrane and the geotextile cover of a partially hydrated geosynthetic clay liner

The migration of gas through a geomembrane overlying a geosynthetic clay liner in a composite landfill cover is primarily a result of the flow through defects in the geomembrane. The nature of the contact conditions between the GCL and the geomembrane is of paramount importance if the leakage rate of a GCL/ GM composite barrier with a defect in the geomembrane needs to be assessed effectively. The present paper reports on interface gas transmissivity measured in a specially made cell. It was found that the gas transmissivity ranged between 2 x 10(7) m(2)/s and 4.5 x 10(-7) m(2)/s for the range of moisture content and differential gas pressure investigated. This corresponded to a reduction of approximately 40% in the gas transmissivity when the moisture content increased from essentially dry to 120%.