Estimation of Peak Acceleration and Bending Moment for Pile-Raft Systems Embedded in Soft Clay Subjected to Far-Field Seismic Excitation

Abstract

An extensive suite of three-dimensional finite-element simulations was carried out to examine the response of pile-raft-soil systems under seismic excitation representative of far-field events. The numerical procedure was first validated by a series of seismic centrifuge tests performed mainly on 4×3 pile-raft systems embedded in soft clays and was subsequently extended to study the influence of various factors on the computed raft acceleration and maximum bending moment near the pile head. The factors considered were pile length, pile flexural stiffness, peak base acceleration, superstructural mass, soil stiffness, soil frictional angle, pile density, and soil-layer thickness. With the help of dimensional analysis, the results of the parametric studies were processed and interpreted using regression analysis to derive correlations for predicting the maximum pile-group bending moment and peak raft acceleration. Such correlations are highly useful in the practical seismic design of pile-raft systems embedded in soft soils, because they provide quick first-order predictions for making initial engineering judgments prior to performing more-detailed and rigorous numerical simulations.