Observations of bentonite erosion from solar-driven moisture migration in GCLs covered only by a black geomembrane

ABSTRACT: Manufacturers of geosynthetic liner materials recommend that composite geomembrane/geosynthetic clay liners (GCLs) be covered in a timely fashion to avoid potential issues that may arise under the action of long-term solar exposure. In this paper, field evidence of a new, never before reported solar-exposure driven damage mechanism for GCLs covered only by a black geomembrane and left exposed for more than 3 years is presented. Solar exposure can give rise to a large daily variation in geomembrane temperature, which causes a moisture cycle within the interface between the geomembrane and GCL resulting in the formation and flow of condensed moisture beneath the geomembrane. All four of the GCL products investigated at the Queen's University Environmental Liner Test Site were shown to have experienced significant bentonite erosion after 4.7 years of exposure. Erosion was identified in the field through a tactile survey of GCL panels in which the stiffness response of the GCL to touch was used to identify eroded zones. A change in the colour of the GCL, although useful to identify possibly eroded zones in some GCL products, proved ineffective in others. Erosion features were observed with widths up to and exceeding 200 mm across, making them unlikely to undergo self-healing upon hydration and application of normal stress. As a result, the observed erosion features would have severe adverse consequences for leakage rates through the GCL component of a composite liner barrier system. These observations provide yet another strong motivation for timely covering of composite landfill liner systems.