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 °C for 16 h; 60 °C for 8 h; 23 °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 ∼75 mm for a 4.42 m wide roll) over the first 5 cycles and 3.8% (∼170 mm) over the first 14 cycles. The shrinkage rate then decreases giving a maximum shrinkage strain of 4.5% (∼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.