Performance of Soil Improvement Techniques in Earthquakes

In the last four decades, there has been a steady trend toward the use of ground improvement as a countermeasure against the hazard of liquefaction. It is well understood that sites with ground improvement suffer less ground deformation and subsidence than adjacent, unimproved areas. However, the lack of quantitative performance data has inhibited the development of empirical relationships between site design parameters such as remediation zone depth and lateral extent and site performance parameters such as ground and building settlement for a given level of earthquake shaking. To date, we have compiled over 90 case histories on the performance of improved sites from 14 earthquakes in Japan, Taiwan, Turkey, and the United States. The collection of field case histories, as the first step towards a greater understanding of the performance of improved soil sites during earthquakes, are summarized in this paper. The field case histories cover a wide range of improvement methods, from conventional densification methods like sand compaction piles to less common lateral restraint-based methods such as sheet pile walls or deep soil mixing grids. The collected data indicate that improved sites generally performed well. About 10 percent of the surveyed sites required significant post-earthquake remediation, repair or demolition. Unacceptable performance designations resulted most often for excessive ground deformations in the presence of a severe lateral spreading hazard or because of an insufficient remediation zone depth