Underground Cave Detection and Generation Mechanism of Unevenness on Artificial Sandy Beach

Unevenness which is sometimes seen on a nourished sandy beach may induce a serious accident, and therefore checking the safety of the nourished beach in advance is important. In this study, field survey to detect underground caves on an artificial sandy beach has been carried out by using a ground-penetrating radar (GPR) system. Also, in the survey site, more than 10 of unevenness were formed just after a heavy rain in the rainy season of 2010. Therefore, the generation mechanism of unevenness has been investigated by analyzing the locations and the underground structure where the unevenness were formed. The result is that the unevenness had been formed by that the nourished sand had fallen into a space between stones lying under the nourished sand. The mechanism has also been confirmed through a simple experiment.