Joint research on the wave-induced liquefaction of sea bed

本文对波浪液化海床进行了分析和实验研究。现将本项目的主要成果总结如下：在松散沉积的海床中存在两种液化类型；一种是伴随累积平均孔隙压力的持续液化，另一种是由振荡孔隙水压力的阻尼和相位滞后引起的瞬态液化。这种液化过程使砂床致密化。利用一维数学模型推导了该现象的动态相似度，并对模型的适用性进行了数值验证，为实验工作奠定了基础。海床中夹带的空气对波浪液化的特征有强烈的影响。为了估计卷入空气的数量，我们尝试采用一种基于地声的测量技术。目前该方法在实际应用中还存在几个问题。在实验室中观测了几种海岸构造周围液化砂的流动情况。本研究建立的数学模型在一定程度上解释了这一现象的动力学行为。对鸟取县Yumigahama海滩发生的一次大规模海岸侵蚀的现场观测表明，海岸附近的波浪液化是造成大规模海岸侵蚀的重要因素。

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.