Comparative Assessment of Single- and Double-Interface Shear Tests of MSW Landfill Liners Using Large Direct Shear Equipment

Geosynthetics form an integral part of engineered municipal solid waste (MSW) landfill lining systems, as they provide cost saving and technical benefits. Their introduction in lining systems, however, has presented new potential interfaces for shear failure especially on bases and on side slopes of engineered MSW landfills. In the laboratory, interface shear strength parameters used in slope designs of landfill lining systems are determined through single-interface testing configurations as per ASTM D5321-20 and D6243-20 standards. However, single-interface testing configurations do not provide a clear understanding of shear strength transfers among the lining components and does not aid in pin-pointing the interface facilitating failure especially when a multi-layered lining system has been proposed. Multi-interface testing configurations present an alternative that may address such limitations. But there is minimum information available on this type of testing as it is not stipulated in any official laboratory testing standard. This study was conducted to provide an understanding of the potential use of multi-interface testing configurations of MSW landfill liners, through identifying similarities and dissimilarities to the single-interface testing configurations. These interface tests were conducted on geosynthetics and geomaterials from a proposed lining system of a new landfill cell in South Africa.