Shear Resistance Characteristics of Soil–Geomembrane Interfaces

The shear resistance at soil–geomembrane interfaces is critically important for the proper design of geomembrane-lined side slopes of landfills, reservoirs, and canals. The dependable design and construction of such applications is enhanced by the experimental documentation of the interaction behavior between different soils and various geomembrane types. Toward this end, direct shear tests were conducted on 29 soil–geomembrane interfaces using a conventional (100 mm) shear box. Two dry and dense uniform sands, one with rounded and one with sub-angular grains of the same size, and one compacted cohesive soil of low plasticity were tested in contact with seven geomembranes of different types with smooth or rough surfaces. The direct shear tests yielded linear failure envelopes with no adhesion for the sand–geomembrane interfaces and polynomial failure envelopes for the cohesive soil–geomembrane interfaces, possibly indicating a transition from drained to undrained conditions at the interface with increasing normal stress. Sub-angular sand grains, soft geomembranes, and rough geomembrane surfaces were found to mobilize interface shear resistance more effectively. The shear resistance parameters are functions of the shearing displacement at the cohesive soil–geomembrane interfaces and their values at failure reveal a transition from “friction-like” behavior to “adhesion-like” behavior as normal stress increases. The ratio between the friction coefficient values for the sand–geomembrane interfaces tested ranges from approximately 1 to 2. For the geomembrane types tested, differences in failure shear stress at the cohesive soil–geomembrane interfaces are generally limited to ± 20%.