The field survey of the 2011 Tohoku Tsunami in Unosumai District of Kamaishi City, Iwate Prefecture suggested the collapse of embankment due to momentary liquefaction. We performed numerical simulation of the effect of pore pressure variation on the stability of embankment. A consolidation model considering saturation of the soil was applied. The numerical analysis demonstrated that the embankment with lower saturation can be unstabilized by the rapid drawdown due to tsunami. Laboratory experiment in the oscillatory flow tunnel also verified that unsaturated sand bed becomes unstable by the rapid decrease in pressure and thus significantly increases the sand transport rate.
