Linear visco-elastic 1D site response of sand-EPS geofoam layers under cyclic loading

A two-part study was undertaken to evaluate the dynamic behavior of sand-EPS geofoam composite layers. The first part aimed at evaluating the dynamic properties of both sand and expanded polystyrene (EPS) geofoam, by performing a series of bender element and strain-controlled cyclic triaxial tests. EPS geofoam with density of 10 and 12 kg/m³ and Chamkhaleh sand with relative density of 55% were tested under confining pressures of 10 and 20 kPa. Normalized shear modulus and damping ratio curves were obtained and compared with the values reported in the literature. They show the dependence of the shear modulus and damping ratio on shear strain, confining pressure and density of the materials. The second part of the study involved linear visco-elastic 1D site response analysis of sand-EPS geofoam layers with different layer arrangements. Results showed that shear modulus attenuation occurs with increase in the volume fraction of the EPS geofoam and this diminution of the response amplitude becomes greater with lower EPS geofoam density. Finally, it was shown that replacing a lumped EPS geofoam inclusion with multiple very thin layers, while maintaining the overall EPS geofoam content, results in a diminished response effect.