Dynamic properties of sand-EPS bead mixtures

Soils modified with Expanded Polystyrene (EPS) beads are typically used as lightweight mixtures to solve many geotechnical challenges. In seismically active areas, understanding the relationship between dynamic properties and strain levels of such mixtures is important for geotechnical applications. The aim of the study is to evaluate the shear modulus and material damping of sand-EPS bead mixtures over a wide range of strains to provide a basis for evaluation of using such mixtures as seismic buffers behind earth retaining structures and for base isolation in seismic areas. Dynamic properties of sand-EPS bead mixtures are evaluated from resonant column and cyclic triaxial tests at small and large strains, respectively. Sand-EPS bead mixtures with varying EPS bead content, up to 2.5% by weight, have been tested at confining pressures of 50, 100 and 200 kPa. Results were analyzed to calculate the small-strain shear modulus, minimum damping ratio, shear modulus degradation curves, and damping curves. Results indicate a decrease in shear stiffness with increasing bead content at all strain levels. Material damping is relatively unaffected at small shear strains; however, it increases at larger strains. The dynamic testing performed yielded properties that can be reflected on applicability of the mixture in geotechnical applications.