ABSTRACT
ABSTRACT: Many sewage manholes and pipes were uplifted during the 1993 Kushiro-oki, the 2003 Tokachi-oki and the 2004 Niigataken-chuetsu earthquakes in Japan. Before the restoration work, detailed soil investigations were carried out to reveal the mechanism of the uplift. Based on the investigations, it was found that the uplift mainly occurred in clayey grounds. 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 research on the sand fill after the earthquake revealed that the sands were very loose and easy to liquefy. Then, it was concluded that the uplift of the manholes and pipes occurred due to the liquefaction of the sand fill.
