Effect of pile type and pile head fixity on the seismic response of a 5 × 5 pile-raft system embedded in a soft clay subjected to far-field ground motions

摘要

Many studies have shown that seismic-induced ground motions can be greatly amplified by soft soil layer(s), which suggests that the installed piles may be subjected to amplified loading even under small or moderate earthquakes. This paper presents results from a series of Three-Dimensional (3D) finite element analyses on different pile-raft systems embedded in a soft clay subjected to a set of three far field ground motions with identical frequency spectra but different peak accelerations. The behaviour of the clay was simulated using a hyperbolic-hysteretic soil model, which was calibrated using laboratory test data from cyclic triaxial and resonant column tests on kaolin clay. The computed accelerations at the clay surface and raft top generally had much larger magnitudes and dominant periods compared to the base motion, due mainly to ground motion amplification and period lengthening effects caused by the soft clay. The peak raft acceleration and maximum pile bending moment were found to approximately linearly increase with the peak base acceleration. Besides, the pile flexural rigidity and pile head fixity (fixed and hinged head) also had a great influence on the pile bending moment response, while the raft acceleration response was comparatively less sensitive to the changes in pile type and pile head fixity.