Mechanisms of Damage to Coastal Structures due to the 2011 Great East Japan Tsunami

Abstract Computational fluid mechanics, field measurements, and empirical methods are used to determine the reasons for the failure of the Kamaishi Breakwater, the Utatsu highway bridge, a concrete girder bridge in Iwate Prefecture, and many small seawalls and buildings during the 2011 Tohoku Tsunami. Results show that the Kamaishi Breakwater failed due to the pressure at the caisson's heel exceeding the bearing capacity of its rubble mound foundation, along with scour of the unarmored landward side of the rubble mound due to the jet resulting from overtopping of the caisson. The Utatsu highway bridge failed due to trapping of air between the bridge's girders, superelevation of the bridge deck toward the ocean, and the presence of a seawall under the bridge. Scour was also liable for the failure of many smaller seawalls and buildings; in some cases this scour was enhanced by rapid-drawdown-induced liquefaction of sandy soils.