Laboratory investigation of unsaturated clayey soil-geomembrane interface behavior

Abstract

Suction-controlled interface direct shear tests were conducted on textured and smooth HDPE geomembrane counterfaces in contact with lean clay. Soil samples were compacted wet of optimum to simulate placement conditions in a composite liner. Tests on saturated samples and soil only were conducted for comparison. Additionally, limited testing was conducted to study the effect of shearing rate on the results. Results reveal that matric suction provided increased shearing resistance, compared to the saturated case, for the textured and smooth geomembrane interfaces, and the extended Mohr-Coulomb envelope provided a good model for geomembrane interface strength. However, strength increases were relatively small compared to soil only, particularly for the smooth interface. Total and water volume changes during shearing were significantly different for unsaturated and saturated conditions. Water volume changes during shearing in saturated soil and interfaces corresponded directly to volume change tendencies during shearing; however, for unsaturated soils this was not the case. Shearing displacement rate was observed to have a profound effect on the shearing resistance of textured geomembranes but had little apparent influence on the smooth geomembrane. Results of this study provide great insight into the unsaturated shearing behavior of clay-geomembrane interfaces and important data for development of constitutive models.