Dynamic load transfer behaviour of piled raft foundations in saturated sand

Abstract

This study investigates the dynamic response and load-sharing mechanism of a piled raft foundation subjected to earthquake loading. A series of 1g shaking table tests was conducted to analyse the dynamic behaviour of soil–structure interaction. The experimental setup involved models of two- and five-story aluminium frame structures supported by a 3 × 3 piled raft foundation embedded in fully saturated Jumunjin sand under both loose and dense conditions. The results reveal that effective stress recovery occurs at varying depths and progresses more rapidly in the lower layers, while the shallower strata experienced excess pore water pressure ratios approaching 1. In loose sand, where piles remain stiff, but the surrounding soil is soft, peak ground acceleration response reached approximately 200% of the input acceleration at intermediate depths, decreasing down to 130% towards the surface. Notably, under dynamic excitation, the load supported by friction piles decreased by 30% and was gradually transferred to the raft as shaft resistance decreased. In contrast, in end-bearing pile conditions, soil compaction and loss of contact with the raft helped maintain pile resistance, allowing the piles to carry approximately 90%–100% of the applied load. These findings highlight the importance of considering soil density and pile bearing type in the seismic design of piled raft foundations, particularly in regions with deep bedrock.