Experimental Investigation of the Shear Behavior of EPS Geofoam

Geofoam has been used in a wide range of geotechnical engineering projects since 1960s; either as lightweight fill material (e.g. embankments and bridge approaches) or as compressible inclusion (e.g. retaining walls and culverts). In most of these projects, geofoam is installed either in direct contact with other geofoam blocks or other construction material. Successful design of these composite systems requires a good understanding of both the compression and shear behavior of the geofoam blocks as well as the shear strength of the interface. In this study, an attempt has been made to measure the shear strength parameters of expanded polystyrene (EPS) geofoam blocks of different densities as well as the interface strength parameters as these blocks interact with sand as well as polyvinyl chloride (PVC) material. A series of direct shear tests has been carried out on geofoam samples of three different densities, namely, 15, 22 and 35 kg/m³. Shear test results on geofoam monoblocks showed that the increase in density results in an increase in the material cohesion, which is associated with a decrease in the internal friction angle. Most of the interface resistance was found to develop at small displacements. For geofoam–PVC interface, both the adhesion and angle of interface friction slightly increased with the increase in geofoam density. The measured geofoam–sand interface strength revealed a consistent increase in the angle of interface friction as the density of geofoam material increased. These experimental results can be used to guide engineers in estimating the interface parameters needed for both analytical and numerical analyses involving soil–EPS–structure interaction.