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The Foundation Input Motion (FIM) arising out of kinematic soil-pile interaction forms an integral part of the seismic analysis of pile-supported structures. Several studies in the recent past have recognized the importance of the filtering effect produced by pile foundations. This paper presents a comprehensive investigation of the influence of raft embedment on the Foundation Input Motion from piled rafts. A hybrid numerical methodology based on the finite element-boundary element method is employed to rigorously model rectangular piled rafts in varying soil conditions. Analysis of transfer functions in the frequency domain suggests that the translational response is suppressed by increasing embedment of the raft. An increase in rocking response is also synchronous with this decrease in translational motion. A transient response analysis carried out using eight different earthquake time histories showed that the spectral acceleration curve is altered by the embedment effect. A set of simplified expressions are proposed to incorporate the embedment effects in the spectral acceleration ratio curve of a pile group. These proposed expressions have the potential to enable a quick estimation of the effect of embedment in the seismic design of pile-supported structures.

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