Engineering Performance of Geosynthetic Clay Liners in Contact with Brine under High Temperature

Geosynthetic Clay Liners (GCLs) have been widely adopted in barrier systems for waste containment facilities. GCLs must be adequately hydrated at all times to maintain their low hydraulic conductivity. However, in several applications the GCL is subjected to high temperatures and its bentonite is therefore at risk of dehydration and desiccation. This is the case in landfills, brine ponds, solar ponds and tailing ponds. Higher desiccation risks have been found in artificial ponds exposed directly to solar radiation. This is due to higher temperature (sometimes >80oC), as well as lower overburden pressures due to the shallow water depth. In addition, the GCL may be exposed to salt solutions. It is therefore that, understanding the behaviour of GCLs under the action of thermal gradients, in the presence of salt, is critical. The main findings of this project can be summarized as follows. The presence of brine resulted in changes in both osmotic and matric suctions in GCLs, as their SWCCs drastically changed when hydrated by a sodium rich brine. GCLs in column experiments experienced high levels of desiccation when subjected to thermal gradients. Creating air gaps between the composite liner and heat source led to a decrease of the temperature to which the GCL was exposed but did not reduce the extent of desiccation and cracking appreciably. Moreover, the polymer-enhanced GCL failed to self-heal when permeated with a sodium-rich brine. On the other hand, the new proposed I-GCLS design succeeded in increasing GCL hydration rates compared to conventional designs. In addition, when subjected to thermal gradients, the new design significantly reduced dehydration and completely prevented cracking. Finally, by adjusting parameters controlling moisture exchange between the liners and subsoils, reasonable predictions of liner system behaviour were obtained by the THM model, including predictions of GCL desiccation when subjected to relatively high heating temperatures (78oC)