Seismic Isolation Effect of Unconnected Piles-Caisson Foundation With Thin Cushion Layer: Large-Scale Shaking Table Tests

This paper reports the results of large-scale shaking table tests on a novel unconnected piles-caisson foundation (UPCF) with a thin cushion layer for seismic isolation. The tests compared traditional thick-cushion and thin-cushion UPCFs under various seismic intensities and wave types. The results demonstrated that the thin-cushion UPCF significantly outperformed traditional thick-cushion designs, achieving a maximum intensity isolation efficiency of 70.1%. This superior performance was attributed to the free rotation of cushion particles, enabling a larger natural vibration period of the cushion. A new evaluation parameter, intensity isolation efficiency, was introduced, which exhibits greater stability and relevancy than peak isolation efficiency. The study also revealed the impact of cushion material, thickness, and seismic wave characteristics on isolation performance, uncovering a nonlinear correlation between square root of acceleration and isolation efficiency. Additionally, an embedded thin-cushion design effectively reduced structural displacement but partly compromised isolation efficiency, highlighting the need for future research to balance these factors. This research contributes to the development of more effective seismic isolation strategies for bridges and other structures in high-intensity seismic zones.