Stress-strain modeling of EPS geofoam for large-strain applications

Both small- and large-strain applications of expanded polystyrene (EPS) geofoam involve interactions with the surrounding geologic materials. The stress-deformation response of this material, however, differs significantly from those of the adjoining geologic materials. A well-justified constitutive law for EPS is, thus, a prerequisite for reliable solutions for soil-structure interaction problems where such material is used. This paper describes a stress-strain law for EPS geofoam for its large-strain applications based on the incremental theory of plasticity. In the derivation of the constitutive relationship, the geofoam was taken as a von Mises material, and it was assumed that the hardening regime follows a hyperbolic curve. The material parameters of the constitutive model were determined from a series of unconfined compression tests performed on EPS specimens of various sizes, shapes and densities. These parameters are functions of the absolute dimensions of the tested specimens as well as the density of EPS. The validity of the model was confirmed by numerical simulations on the compression testing program of EPS geofoam.