ABSTRACT
Pile foundations are widely used both onshore and offshore to transfer heavy structural loads to competent load bearing soil strata or bedrock. Geotechnical engineers are called upon to design deep foundations when the shallow layers of soils beneath the building are either unable to support the loads imposed by the superstructure on the shallow foundations or if the shallow layers may become unstable due to the cyclic shear stresses induced by the earthquake loading. Under such circumstances it is imperative to look for pile foundations that transfer the load from the superstructure to more firm and stable soil strata at deeper levels or onto bedrock. In this chapter the seismic design of pile foundations is considered in the light of the EC8 Part 5 (2003) provisions as well as some of the current research findings. It is perhaps helpful if some of the well-known examples of failures of pile foundations during or following an earthquake loading are considered first. 9.1.1 Examples of pile foundation failures following earthquake loading
Although pile foundations are widely used in the regions of high seismicity around the world, there are a number of examples where the pile foundations have failed during strong earthquake events. Such failures can cause either collapse of the superstructure or excessive settlements and rotations. During the 1964 Niigata earthquake the Showa Bridge collapsed as shown in Figure 9a. Figure 9b shows one of the piles that was extracted during the post earthquake investigation, while Figure 9c shows the schematic diagram of the collapsed spans.The Showa bridge collapse was attributed to many causes. For example, Hamada (1992) proposed that lateral spreading of the soil following liquefaction (see Figure 9c) caused large displacements at the pile heads and resulted in the dislodging of the spans. Bhattacharya et al (2005a) have proposed that buckling of the piles in liquefied sands could have caused the collapse of the Showa Bridge. The Showa Bridge collapse is not a unique event. There have been many other failures involving pile foundations.
