Joint research on the wave-induced liquefaction of sea bed

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In this research project the wave-induced liquefaction of sea-bed is treated analytically and experimentally. The main results of this project are summerized below.1.There are two types of liquefaction in the loosely deposited sea-bed ; one is sustainable liquefaction which is accompanied by the built-up mean pore pressure and the other one is transcient liquefaction caused by the damping and phase lag in the oscillating pore water pressure. The sand bed is densified by such process of liquefaction.2.The dynamic similitude of this phenomenon was derived by using the one-dimensional mathematical model and the applicability of the model was verified numerically, thereby the basis for the experimental work was made clear.3.The entrained air in the sea-bed affect strongly the feature of the wave-induced liquefaction. To estimate the quantity of the involved air, we tried to adopt a measuring technique based on geo-acoustics. At present there are several problems in the method for the practical use.4.The flow of liquefied sand around several types of coastal structures are observed in the laboratory. The dynamic behavior of this phenomenon is explained to some extent by the mathematical model developed in this research.5.It has been shown through the field observation of a large scale coastal erosion occured in Yumigahama beach in Tottori Prefecture, the wave-induced liquefaction near the coast is an important factor to cause such a large scale erosion.