EPS beads-sand mixtures for geotechnical seismic isolation: performance and mechanisms

Expanded polystyrene (EPS) possesses material properties well suited for geotechnical seismic isolation (GSI), including low modulus, low density, and very low seismic impedance. When incorporated into foundation soils, such low-modulus materials reduce both the horizontal and rocking stiffnesses of the foundation system, while the pronounced impedance contrast with surrounding soils modifies seismic wave transmission. In this way, both inertial and kinematic soil-foundation-structure interaction can be deliberately exploited as isolation mechanisms. This study investigates the potential of EPS beads-sand mixtures for GSI by examining the seismic response of two GSI configurations. A series of geotechnical centrifuge tests was conducted using 12 input earthquake ground motions. The results demonstrate that EPS beads-sand mixtures can provide effective seismic isolation, with peak structural response demands reduced by over 50% on average, while also limiting foundation uplift and mitigating shaking-induced ground settlement, thereby providing new experimental evidence for GSI mechanisms and isolation performance.