Case history of liner veneer instability

Abstract

Construction conditions experienced during installation of a landfill geocomposite liner system led to two slides on a 3H:1V slope during construction. The landfill was being developed for final disposal of flue gas desulfurization by-product material (FGD). The slides occurred in two different areas of the 3H:1V slope and encompass 10,500 and 20,235 m2 in the Fall of 1996 and Summer of 1997, respectively. The slides developed by movement along the PVC geomembrane/compacted clay liner interface during or shortly after placement of the protective FGD cover material over the drainage sand layer. Laboratory direct shear tests revealed that the shear strength of this interface is sensitive to the moisture content of the exposed compacted clay liner. The direct shear tests revealed reductions in the available shear strength of 35% and 37% for the peak and large displacement values as the compacted clay liner moisture content increased by 8 percentage points. In addition, shear stresses induced by surface traffic activities might result in shear displacements along the interface, which in some cases were large enough to lower the available shear resistance of the geomembrane/compacted clay interface to a post-peak or large displacement value. This paper discusses the slides, direct shear testing, slope stability analyses used to evaluate the mobilized interface shear strength parameters, the relationship between moisture content and geomembrane/compacted clay liner interface strength, and the effect of shear displacement on the mobilized shear strength.