Author(s): Shinji Kioka; Maiko Ishida
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Abstract: Sea ice carried to land by tsunamis has been reported to cause serious damage to private houses and bridges from the impact of the ice floes (e. g., in the 1952 Tokachi-Oki Earthquake). In this study, some new experimental results and theoretical considerations were added to reexamine the phenomena of run-up tsunamis containing ice in addition to our previous studies. We suggested the following mechanisms/processes behind the action of force caused by a tsunami with ice. After the collision force imparted by the ice floes acts on structures, the tsunami flow is blocked by the formation of ice jams between the structures, and a large static force also acts on the structures because of the ice jam formation. Even after the water subsides, horizontal force caused by ice pile-up, such as active earth pressure, remains. It was confirmed that the active pressure and the residual force could be estimated by Rankine's earth pressure theory when ice fragments were regarded as Mohr-Coulomb materials. A simple theoretical model was developed to estimate the water depth and the tsunami force on structures caused by tsunami run-up flow using only a parameter as the open ratio instead of structure width and pitch, which was modeled by analogy to the occurrence of a negative bore caused by the sudden closing of a sluice gate. The validity of the simple theoretical model was also confirmed by the further experimental results in this study. It was also found that, when the ice jam formed, although there was dispersion in the water depth in front of the structures and there was no clear difference between the open ratios, the water depth was roughly the same value as that in the case with less than 0.3-0.4 of the open ratio under a no-ice.
Year: 2018