EVALUATION OF THE STABILITY OF VARIOUS TYPES OF COASTAL DYKE AGAINST OVER-FLOWING TSUNAMI CURRENT

Abstract

During the 2011 Great East Japan Earthquake, at many places, fill-type coastal dykes fully collapsed by over-flowing tsunami current by two mechanisms. Mechanism A: the subsoil in front of the downstream slope was scoured, which destabilized the concrete facing on the downstream slope. Mechanism B: the concrete panels on the crest and the downstream slope were lifted up and flowed away by the tsunami current. The backfill was then quickly eroded. Based on small-scale model tests in the laboratory, to prevent Mechanism B, as well as to increase the seismic stability, it is proposed to reinforce the backfill,cover the slopes and crest with concrete panels connected to each other and to the reinforcement layers.