Experimental Study on Monotonic and Cyclic Shear Behaviors of EPS Geofoam and Its Interfaces with Structures

Abstract

This study experimentally investigates the shear behaviours of Expanded Polystyrene (EPS) geofoam and its interfaces with structures through simple shear tests. The results demonstrate that the shear behaviours of EPS is predominantly governed by EPS density and vertical stress. Under monotonic shearing, EPS exhibits strain-hardening behaviour, with the apparent shear strength controlled by the equivalent cohesion that increases linearly with density. Under cyclic shearing, EPS forms symmetric hysteresis loops. The secant shear stiffness increases with EPS density and vertical stress, while the equivalent damping ratio exhibits an opposite trend. Significant irrecoverable volumetric contraction accumulates nonlinearly with the number of cycles. For the EPS-structure interface, the shear mechanism transitions from friction- dominant mechanism (exhibiting ideal plasticity) to adhesion-dominant mechanism (exhibiting strain hardening) with increasing vertical stress or decreasing EPS density. Under cyclic interface loading, a progressive degradation of shear stiffness and damping ratio was observed. Using 3D laser scanning, a direct correlation was established between interfacial mechanical response and the evolution of surface roughness on the EPS specimen. These findings provide reliable data and insights for designing EPS-based geotechnical systems such as lightweight embankments and seismic buffers.