Abstract
In this paper, the authors focus on the flotation mechanism of underground structures induced by liquefaction of the ground during/after an earthquake and the method of countermeasure designing for it. As for the flotation mechanism, it is guessed that the soils to the bottom of the structure from the circumference during floating were supplied. This guess is based on the assumption that the flotation occurred by the difference of effective pressure at the bottom of the structure and the ground around the bottom. As for the countermeasure method, it thought that floating could be delayed by installing a fin in the base part of the structure and interrupting this supply. This way of thinking was confirmed by shaking table tests performed respectively four times on the soils with buried structure case, no-countermeasure case, and the countermeasure case. Next, the establishment of an evaluation method of the safety against flotation is surely necessary in the design. In finite element analysis, it was examined through the simulation of shaking table tests if finite element analysis could be used as an evaluation of the safety against the flotation. As a result of this study, flotation is influenced by the difference in pressure, the proposed countermeasure method is effective and flotation can be reproduced by the analysis.
