2015 Volume 29 Issue 2 Pages 124-131
East coasts of Hokkaido, facing Okhotsk Sea and Pacific Ocean, are covered by sea ice drifted from northern Okhotsk Sea in late January through early of March. When tsunami occurs during the term and arrives at the ice-covered coasts, the disaster risks are significantly increased since ice floes carried by run-up tsunami can extend the possible damages through distinct dynamic behaviors occurring in ice-floe-laden flows; that is, forming pile-ups and jams of the ice floes, and enhancing ice and hydraulic forces. In this paper, features of the previous damages to residences and infrastructures by sea ice for the 1952 Tokachi-oki tsunami and the 2011 Tohoku tsunami are firstly discussed for charactering the ice-structure interactions. The fracture mechanisms of the ice floes colliding to structures during jamming and piling-up processes are identified on the basis of model experiments as well as numerical computations using a 3D Distinct Element Method. We also find structures with openings, such as windows and space between columns, induce ice jams and pile-ups and dam up the run-up flows, resulting in downstream water level rise and thus significant increase of hydraulic pressure acting on the structure, which indicates the increased risks expected in urban area.
