Small-strain dynamic characteristics of multilayered rubber-sand composites

The rubber sand mixture (RSM) is an effective seismic isolation material, and understanding its layered structure is essential for optimizing its performance in geotechnical earthquake engineering. This study investigates the dynamic characteristics of multi-layered RSM composites, identifying the optimal rubber content (RC) and initial parameters for their use as buffers. To this end, a series of resonant column tests were conducted to compare the differences between layered rubber-sand (LR-S) and conventional RSM by measuring their dynamic shear modulus and damping ratio at small strain amplitudes. The experiments on LR-S involved constructing configurations with three-, five-, and seven-layer structures, while varying the RC and confining pressure to assess their influence on the composite’s dynamic behavior. Results show that the dynamic shear modulus of LR-S is reduced by 6–13 times compared to RSM. Additionally, the damping ratio of LR-S decreases with increasing RC, contrasting with RSM behavior. As confining pressure rises, the damping ratios of pure sand and RSM decrease, whereas the damping ratio of LR-S increases, akin to pure rubber. Additionally, LR-S demonstrates a continuous upward trend in damping ratio with increasing shear strain. These findings are pivotal for designing effective seismic mitigation and underground isolation systems.