Author(s): Shinji Kioka; Takahiro Takeuchi; Naohiro Maruta
Keywords: No Keywords
Abstract: If a tsunami in ice-covered sea reaches the coast, run-up waves carrying ice may causegreater damage than regular waves due to their dynamic action occurring in ice-floe-laden flows; that is, forming pile-ups and jams of the ice floes in addition to the collision force by the ice floes. In the past, some damages to residences and infrastructures by ice floes at the time of the 1952Tokachi-oki tsunami and the 2011 Great Tohoku tsunami have been reported so far. This paper reviews the results of a previous model experiment by the authors on tsunamirun-up containing ice, adds some new observations and gives suggestions to contribute to measures for the mitigation of disasters. 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 water level rise and because of hydrostatic pressure between the structures due to the ice-jam. Even after the water subsides, active pressure caused by ice pile-up remains. Some proposals were also made from a practical viewpoint. In designing of facilities with openings such as windows and gaps in piloti structures especially in regions prone to lots of tsunami-related debris such as timber, cars and containers as well as ice floes, the design force acting on such parts should not be reduced because of the jamming. It is also necessary to evacuate to higher places than for no-ice tsunami due to increased water levels and pile-up. In addition, a quasi-3D DEM was developed with consideration of vertical motion in a 2D DEM in order to simulate pile-up and ice jam formation, and an example of results obtained from simulating the run-up of ice floes caused by a tsunami was presented. Such calculation was expected to be useful for the compilation of hazard maps and the development of disaster mitigation plans in the future.