Physical modelling of nonwoven/nonwoven GCL shrinkage under simulated field conditions

A physical model was employed to evaluate the potential shrinkage of a needle-punched nonwoven/nonwoven geosynthetic clay liner (GCL) subjected to simulated daily heating/cooling cycles (23 degrees C for 16 h; 60 degrees C for 8 h; 23 degrees C for 16 h etc. at the top) modelling solar exposure conditions of an overlying black geomembrane and simulated field moisture conditions where the GCL must rehydrate with water from a silty sand foundation soil with an initial moisture content of 16-17% in a closed system. It is shown that when the GCL was allowed to hydrate to 110% gravimetric moisture content before being subjected to daily heating/cooling cycles there is a relatively rapid increase in maximum shrinkage strain to 1.7% (corresponding to shrinkages of similar to 75 mm for a 4.42 m wide roll) over the first 5 cycles and 3.8% (similar to 170 mm) over the first 14 cycles. The shrinkage rate then decreases giving a maximum shrinkage strain of 4.5% (similar to 200 mm) after 50 heating/cooling cycles. Experiments are conducted for the GCL with different initial gravimetric moisture contents and it is shown that the initial moisture content at the time the heating/cooling cycle commenced has a substantial effect on shrinkage. Consistent daily cycles of the magnitude examined are shown to suppress GCL shrinkage, but a cool period during which the GCL can hydrate from the subsoil, followed by significant daily thermal cycles, increases the shrinkage. The implications with respect to field shrinkage are discussed. (C) 2013 Elsevier Ltd. All rights reserved.