Gas permeability of geosynthetic clay liners

Series of gas permeability tests were performed on partially saturated needle-punched geosynthetic clay liners (GCLs) with nitrogen (N-2) as the gas permeant medium. The hydration procedure was found to have a strong influence on the gas permeability of the GCLs. For the range of overburden pressures considered in the present investigation, a reasonable linear relationship on a linear-log scale has been observed between the permeability and the volumetric water content. A decrease of around 1 to 1.5 order of magnitude in the permeability of a granular bentonite type of GCL and about 2 to 3 order of magnitude in the permeability of a powder bentonite type of GCL have been observed for the range of volumetric water content studied (46% < theta < 73%). A well defined linear relationship was found to exist between the permeability and the air content. This relationship is independent of the overburden pressure and is specific to each type of GCL. The size and shape of the gravel in the drainage layer immediately above the GCL was found to affect its gas permeability, when subjected to high overburden pressure. (C) 2000 Elsevier Science Ltd. All rights reserved.