Effect of Soil Fines on Geosynthetic Interface Shear Strength

The interface between a geosynthetic drainage composite (GDC) and textured geomembrane (GMX) is assumed to be free of soil particles and other debris to facilitate drainage, maintain interface shear resistance, and minimize clogging. However, soil particles usually can pass through the GDC and accumulate on the upper surface of the primary-GMX during landfill construction and operation. This paper presents a case study involving a geosynthetic bottom liner system with a leachate collection and removal system above the primary-GMX comprised of granular drainage media and an underlying GDC. After exhumation, the primary-GDC/GMX interface contained significant soil particles while the secondary-GDC/GMX interface did not. Torsional ring shear tests were conducted to study the impact of the soil particles on the primary- and secondary-GDC/GMX interfaces to understand why failure occurred along the top of the secondary-GMX and not the primary-GMX even though similar geosynthetics were used for both interfaces.