Nondestructive Shear Stiffness Evaluation of EPS-Sand Composites Using Quartz and Calcareous Aggregates

The influence of expanded polystyrene (EPS) beads inclusion on the shear stiffness of a quartz-based material and a calcareous-based material has been examined by performing a comprehensive series of non-destructive bender element tests. To this end, siliceous-based Firoozkooh and calcareous-based Hormuz sands are mixed with different percentages of expanded polystyrene beads and then tested with a bender element apparatus embedded in a triaxial cell. Accordingly, the influences of confining pressure, void ratio, grain size distribution, and different percentages of expanded polystyrene beads on the small-strain shear modulus of siliceous and calcareous sands are thoroughly studied and discussed. For all mixtures of both sands, the maximum shear modulus increases with increasing confining pressure, but decreases with increasing void ratio and expanded polystyrene beads content in the mixture. The contribution of expanded polystyrene beads to the reduction of small-strain shear modulus is observed to be more pronounced for the quartz-based aggregate as compared to the calcareous-based aggregate. The confining pressure is also observed to have no influence on the small-strain shear modulus of the composites at high expanded polystyrene bead contents due primarily to the notably high compressibility of soft beads diminishing the augmented interparticle contact forces caused by increasing isotropic confinement. Using the results of experiments, different small-strain shear modulus expressions are developed for quartz-based and calcareous-based compacted fill-expanded polystyrene beads composites, which can be utilized for design purposes in earthen structures.

Use of lightweight fill materials in various civil engineering applications has always been of great interest to engineers. Such materials are commonly utilized to reduce excessive settlements and lateral pressures and to increase the safety factor of geotechnical structures such as man-made slopes. Expanded polystyrene (EPS) as a kind of lightweight material can be employed for filling purposes in slopes and highway embankments, lightening of backfill soils, reducing lateral earth pressures on retaining structures and cutting down construction costs. Use of such materials not only provides a lightweight fill solution, but also helps to save the environment by recycling these materials instead of stockpiling them. Mixing granular soils with EPS beads to enhance their geotechnical properties has recently gained great attention from the geotechnical engineering community. As 40% of the ocean floor surface is covered with carbonate soil, the use of EPS beads-carbonate sand mixtures for engineering applications is favorable to practitioners. Results of this study show that the addition of EPS beads leads to a reduction in the overall stiffness of composites. Moreover, the effect of EPS beads on the shear stiffness of mixtures is related to the properties of the host sand, including grain shape and minerology.