Monotonic, cyclic and post-cyclic shearing behavior of sand-EPS geofoam interface

Sand-EPS geofoam is commonly used as a seismic buffer in a variety of geotechnical applications to alleviate damages imposed by seismic vibrations. Evaluation of the properties of the sand-EPS geofoam interface is an essential part of the design and installation of EPS geofoam in direct contact with the parent sand. In this study, a series of laboratory tests are carried out using a large-scale direct shear apparatus to evaluate the monotonic, cyclic and post-cyclic behavior of the sand-EPS geofoam interface. Adopting the relative density of the parent sand, the density of EPS geofoam, the applied normal stress, the cyclic shear strain semi-amplitude and the number of cycles as the variable parameters, their influence on the response of the sand-EPS geofoam interface is investigated. According to the experimental results, with the increase in the number of cycles, sand relative density, EPS geofoam density and the applied normal stress, the equivalent or secant stiffness of the sand-EPS geofoam interface increases while its damping ratio declines. The results of the monotonic (MDS) and post-cyclic monotonic (CMDS) shearing experiments also show that with an increase in the EPS density and normal stress, which offers greater resistance against sliding, the mobilized shear stresses generally increase.