In order to explain the landing posture of artificial reef block on the sea bottom throw down from the barge, we made the experiment to clarify the rolling motion of falling block in the water, and measured the period and amplitude of the rolling motion of several model block bodies in experimental cylindric water tank. The results were as follows : Ro11ing period and amplitude were related to the parameter (Iん2) obtained by the inertia moment J (g. cm2) and steady falling velocity u (cm/s) of

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... he block bodies. Rolling period was sli如tly increased with growth of Iん2, but rolling amplitude slightly decreased with this. It was assumed that when the large reef block was falling in sea water, the rolling inotion was Ionger in period and smaller in amplitude than the smaller model block bodies. Furthermore言t was suggested that the rolling motion of the falling block body in the water can be estimated by dynamic analysis theoretically.