Development of a hyperbolic constitutive model for expanded polystyrene (EPS) geofoam under triaxial compression tests

Triaxial tests were conducted to develop a constitutive model of cellular type expanded polystyrene (EPS) geofoam block under short-term (immediate) loading. Specimens of EPS geofoam with densities of 15, 20, 25, and 30 kg/m(3) were tested under confining stresses of 0, 20, 40, and 60 kPa. Test results show that EPS geofoam displays nonlinear major principal stress-strain behavior, which is a function of confining stress and density, and a higher maximum compressive strength with increased density and confining stress. The EPS geofoam exhibits directional deformation along the axis of major principal strain with no dilative shearing, and the generated axial and volumetric strains produce a linear correlation that is a function of density and confining stress. From the test results, a new hyperbolic model simulating the stress-strain behavior of EPS geofoam is proposed. This model includes the major principal stress and strain as well as density and confining stress. Strain-dependent tangent modulus and Poisson's ratio influenced by the confining stress and density of the EPS geofoam are derived from the model. The model shows the elastic tangent modulus and Poisson's ratio increase with density and decrease with confining stress. Compared to previous models, the proposed hyperbolic model is shown to give best fit to the measured test data. (C) 2004 Elsevier Ltd. All rights reserved.