Gas permeability tests of partially saturated needle punched GCL showed that the intrinsic gas permeability was very sensitive to the change of gravimetric moisture content and volumetric water content. For the conditions examined, it was found that the desiccated GCL tended to have higher intrinsic gas permeability than the hydrated GCL at a comparable gravimetric moisture con tent, as desiccation leads to shrinkage and the formation of desiccation cracks of the bentonite component. The results imply that hy-drated GCL in cover system must be properly protected from desiccation, as there is strong possibility for gas to escape if the GCL starts to desiccate. Furthermore, the tests showed that the presence of overburden pressure during hydration could reduce intrinsic gas permeability of hydrated GCL indicating that the GCL should be subjected to confinement at time of installation or hydration.
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