Performance of Piled Raft Foundation with Grid-Form Ground Improvement During the 2011 off the Pacific Coast of Tohoku Earthquake
Akihiko Uchida*, Kiyoshi Yamashita*, and Nobuyuki Odajima**
*Research and Development Institute, Takenaka Corporation, 5-1, 1 Chome, Ohtsuka, Inzai, Chiba 270-1395, Japan
**Building Design Department, Takenaka Corporation, 1-1, 1 Chome, Shinsuna, Koto-ku, Tokyo 136-0075, Japan
Grid-form ground improvement by the deep cement mixing method is one of the countermeasures against soil liquefaction. Improvements by this method were confirmed during the southern Hyogo Prefecture Earthquake in 1995. The number of building foundations adopting this method has increased in the last years. During the 2011 off the Pacific coast of Tohoku Earthquake, which occurred on March 11, severe liquefaction damage was observed in reclaimed land in the Tokyo Bay area. Since then, liquefaction countermeasures have been recognized to be important to reclaimed land. A building foundation improved by grid-form ground improvement method is introduced in this paper. Field investigation results of ground around the building after the 2011 earthquake are presented. The effect of liquefaction prevention on gridform ground improvement is discussed based on dynamic nonlinear analysis of soil layers with actual acceleration records. Comparing field investigation results to simulation analysis, we concluded that gridform ground improvement prevented liquefaction of original soil surrounded by grid-form walls during the 2011 earthquake.
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