UPLIFT OF SEWAGE MANHOLES AND PIPES DURING THE 2004 NIIGATAKEN-CHUETSU EARTHQUAKE(<Special Issue>Geotechnical Disasters in 2004 and 2005)

概要

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About 1,400 sewage manholes were uplifted during the 2004 Niigataken-chuetsu earthquake in Japan. Many buried sewage pipes were also uplifted. Before the restoration work, detailed soil investigations were carried out to reveal the mechanism of the uplift. Based on the investigations, it was clarified that uplift occurred in mainly clayey grounds. No sand boils were observed on the clayey ground. However, boiled sands were observed just beside the uplifted manholes and above the buried pipes. During the construction of buried pipes and manholes, the ground was excavated first, the pipes and manholes were placed in the ditches, then the ditches were filled with sand. The soil investigation of the sand fill after the earthquake revealed that the sands were very loose and easy to liquefy. It was concluded that the uplift of the manholes and pipes occurred due to the liquefaction of the sand fill. In preparation for the restoration work, appropriate countermeasures for future earthquakes were discussed, and finally, the cement mixing method was selected.
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