Kinematic Response Characteristics of a Piled Raft Foundation-Paper

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The study investigates how an embedded raft affects the earthquake-induced kinematic response and dynamic impedances of piled raft foundations. The authors use a three-dimensional finite-element substructuring method implemented in ACS SASSI, explicitly modelling the soil between piles to capture pile–soil and raft–soil interactions. The method is checked against published analytical results for a pile group and centrifuge-test data for a piled raft in clay, with generally good agreement.<br /><br />The main analyses examine a four-pile raft in clay for pile spacing-to-diameter ratios of 4–10. Results show that pile layout strongly influences rocking: peak rotation approximately doubles as spacing increases from 4 to 10. The raft’s effects vary with frequency. It increases translational motion in the dimensionless-frequency range of about 0.4–0.65, with translation reported to rise by as much as three times. At low frequencies (up to about 0.25), the raft reduces rotation; its effect at higher frequencies depends on pile configuration.<br /><br />Comparisons with corresponding pile groups also show that the raft substantially reduces dynamic stiffness over a dimensionless-frequency range of roughly 0.23–0.6 and increases damping above about 0.4. These findings indicate that raft embedment and pile arrangement can materially alter foundation input motion, rocking, stiffness, and damping. The authors conclude that raft effects should be included when assessing seismic soil–structure interaction for piled raft foundations.

Keywords

piled raft foundation

embedded raft

earthquake response

dynamic impedance

soil-structure interaction

pile-soil interaction

raft-soil interaction

rocking motion

finite element analysis

seismic engineering