Narrow Results

This paper examines the seismic response of clay pile-raft system with flexible and stiff piles using centrifuge and numerical studies. Centrifuge studies showed that interaction between pile-raft and clay will cause a significant softening in the clay adjacent to the pile-raft which produced a lengthening of resonance period in near-field soil compared to the far-field soil. The difference of response among the raft and the soil at both near- and far-field indicates that ground motion at both near- and far-field cannot be representative of raft motion. There is also significant difference between flexible and stiff pile response. It has been shown in a previous study that, for stiff pile, the soft clay acts as an inertial loading medium rather than a supporting medium. For this reasons, the bending moment diagram extends deep into the soft soil stratum. However, for flexible pile, the supporting effect of the surrounding clay is much more significant than in stiff pile. As a result, the bending moment envelope for flexible pile under earthquake shaking is very similar to the head-loaded test results, with an active length of pile below which no significant bending moment occurs.

One of the important factors in the amplification of seismic waves arriving the ground surface is site effects. Site effects, known as topographic irregularities, lead to seismic wave scattering, and this phenomenon can amplify or reduce the displacement recorded in different parts of a site. Therefore, it is necessary to investigate these effects for an accurate evaluation of the dynamic response of the structures built on these sites. One of the topics that has been given little attention is the interaction effects of topographic irregularities on each other’s dynamic responses. Using the three-dimensional boundary element method (3D-BEM) in the frequency domain, this study investigated the dynamic response of the site with canyons and hills adjacent to each other at different intervals and under SH seismic waves with different angles and dimensionless frequencies and with the hill in different geometries (semi-elliptical, triangular, semi-circular). The obtained results indicated that parts of the canyon that are adjacent to the hill underwent the greatest amplification, especially when the distance between the canyon and the hill is small. It was also found that the incident angle of the waves is one of the important parameters in the obtained displacement pattern on the site. Although the wave hit the canyon-hill site vertically, the results revealed that an asymmetric displacement pattern was experienced on the dynamic response of the site due to the phenomenon of amplification of seismic wave dispersion.