ABSTRACT

When designing pile foundations to be constructed in improved ground, there is no reasonable and unified method for determining the subgrade reaction characteristics after ground improvement. Consequently, there is also no systematic seismic design method that considers the influence of the dynamic behavior of the improved ground on pile foundations during earthquakes. The authors have developed a reasonable construction method of pile foundation in which, prior to installing piles, the ground is improved around the heads of the piles in soft ground or ground subject to liquefaction during earthquake (Tomisawa & Nishikawa 2005a; b). In this method, the increased shear strength due to ground improvement is reflected in the horizontal resistance of the pile. This method uses a combination of pile foundation construction and common ground improvement methods, including deep mixing, preloading, and sand compaction piling, and is referred to as the composite ground pile method.