Field Performance of Exposed Geosynthetic Composite Liner Systems

Abstract

Geosynthetic clay liners (GCL) overlain by a geomembrane (GMB) in a geosynthetic composite liner system in landfill liner and other waste containment applications can be left exposed for weeks, months, or in some extreme cases, even years. Three known consequences of leaving a GMB-GCL composite liner system uncovered, namely geomembrane wrinkling, GCL panel shrinkage, and more recently down-slope erosion of bentonite from a GCL are investigated in a second field experiment at the Queen’s University Environmental Liner Test Site (QUELTS II). Wrinkles were quantified for black and high albedo white high-density polyethylene geomembranes (both smooth and textured). Relative to the black geomembrane, wrinkles in the white geomembrane formed later in the morning and reduced sooner in the evening. Wrinkles in the white geomembrane relative to the black were less frequent, smaller in height, and had much shorter maximum interconnected lengths. GCL panel shrinkage and solar-driven down-slope bentonite erosion were quantified for four GCLs (two powdered bentonite GCLs, one polymer enhanced bentonite GCL, and one multicomponent GCL with a polymer coating installed coating up) left covered only by a black geomembrane, and for one GCL (containing fine-grained granular bentonite) left covered by a black geomembrane, white geomembrane, or 0.3 m of gravel cover. All GCLs experienced some overlap reduction except the GCL covered by gravel, although no loss of panel overlap occurred during 28 months of monitoring. If immediate cover is not possible, the choice of GCL type and the use of a white geomembrane can result in slower shrinkage rates. In addition to timely covering, GCL selection can reduce bentonite susceptibility to down-slope erosion. The polymer coated GCL (coating up) was found to be the most resistant to down-slope erosion, while the polymer enhanced and powdered bentonite GCLs were all far more resistant to erosion than the fine-grained granular bentonite GCL, although no erosion features with bentonite loss were detected on any GCL within the first seven weeks of exposure following the May 2012 construction. The use of a white geomembrane reduces the thermal effects on the composite liner, but ultimately did not prevent solar-driven down-slope bentonite erosion.