Effect of GCL Properties on Shrinkage When Subjected to Wet-Dry Cycles

The potential shrinkage of eight different geosynthetic clay liners (GCLs) subjected to wetting and drying cycles is examined. It is shown that the initial (e.g, off-the-roll) moisture content may affect the initial shrinkage but did not notably affect the final equilibrium shrinkage. For GCLs with granular bentonite and wetted to a moisture content of about 60% (or greater) in the hydration phase, the actual moisture content did not appear to affect the magnitude of the final equilibrium shrinkage. However, it did affect the rate of shrinkage. Specimens brought to about 100% moisture content in each cycle reached a constant shrinkage value much faster than those brought to about 60% in each wetting cycle. GCLs containing powdered bentonite generally shrank more than those containing granular bentonite. All of the powdered bentonite specimens continued a slow accumulation of strain with increasing cycles, even up to 75 cycles. The shrinkage of a needle-punched GCL with a thermally treated scrim-reinforced nonwoven carrier geotextile and granular bentonite was less than that for a needle-punched GCL with a simple nonwoven carrier and granular bentonite. For some products, there was considerable variability in GCL shrinkage for specimens from the same roll and tested under nominally identical conditions, whereas for other products, the variability was relatively small. The shrinkage strain required to cause the loss of a 150–300 mm panel overlap is shown to be able to be mobilized in about five wet-dry cycles in the experiments reported.