Stress-strain responses of EPS geofoam upon cyclic simple shearing: Experimental investigations and constitutive modeling

This paper investigates the cyclic simple shearing behaviors of Expanded Polystyrene (EPS) geofoams considering influences of the shear strain amplitude (γ_a), number of shear cycles, shear rate, vertical stress (σ_n), and EPS density (ρ_EPS). The experimental results demonstrate that the cyclic shear stress (τ)-shear strain (γ) relationships of EPS are not sensitive to the shear rate. As the γ exceeds 2%, the EPS yields and its τ-γ relationships and backbone curve become nonlinear. There are linear relationships between the elastic modulus E, elastic shear modulus G_e, and plastic shear modulus G_p. They increase linearly with an increase in the ρ_EPS. The G_e and G_p are not sensitive to the γ_a. The cyclic shear stiffness G increases while the equivalent damping ratio D of EPS decreases with an increase in the σ_n and ρ_EPS. The G decreases while the D increases nonlinearly as the γ_a increases. Empirical models were developed to describe the variations of the G_e, G_p, G, and D with σ_n, ρ_EPS, and γ_a. A modified Hardin-Drnevich model was proposed to describe the backbone curves and τ-γ loops upon cyclic simple shearing, which has achieved good agreement with the experimental measurements and the testing results from the literature.