Influence of pile rake angle on the seismic response of pile foundations and piled structures

Abstract

Even though inclined piles have traditionally been used to withstand large horizontal loads, the lack of understanding about their response under seismic loads (or under associated loads derived, for instance, from soil settlementor liquefaction) have prevented their use in seismic regions. However, several authors have showed that inclined piles may provide potential benefits with respect to the seismic response of the superstructure and of the foundation itself. For this reason, the dynamic responseof this type of foundations isnow being studied. The kinematic interaction factors of pile foundations with inclined elements is one of the aspects that have not received enough attention. The influence of pile rake angle on the seismic response of the superstructure is another aspect that still needs more research. These are precisely the two aspects on which this paper will focus.In order to compute kinematic interaction factors, a three-dimensional boundary element –finite element coupling formulation is used. The system is excited by harmonic vertically-incident shear waves.The paper presents kinematic interaction factors corresponding to inclined single piles, and square 2 by 2 and 3 by 3 pile groups in ready-to-use dimensionless format. It is shown that, while the kinematic response of inclined single piles is rather independent of the rake angle, the kinematic restriction of the pile cap produces a significant dependence on that factor: horizontal displacements are reduced with the rake angle, while rotation changes sign for a certain configuration and increases significantly afterwards. These results can be used to compute the response of a superstructure by substructuring in order to study further the influence of rake angle on it.