Experimental Study on Breakwater Against Overflow and Big Waves

Coastal structures face the risk of destruction on a catastrophic scale from the huge hurricanes and tsunamis occurring as of late. The extensive damage that these storms inflict on coastal structures stresses the need to design coastal structures that can withstand and operate appropriately against a variety of complex phenomena. However, the phenomena triggering such disasters neither not fully investigated nor understood; for instance, one such phenomenon is the superposition of high waves and high tide as the likely cause of damage to breakwaters. To clarify such a complex phenomenon, we conducted a series of experiments focused on breakwater stability against the superposition of high waves and overflow.

The result of the experiments made the following clear: First, the water pressure at the front wall of the caisson corresponds to the superposed pressure of overflow and waves. On the other hand, the water pressure at the rear wall was mainly affected by overflow but not by the waves. Thus, breakwaters can be exposed to the higher risks of sliding and overturning due to the superposed force of overflow and waves. Secondly, the wave pressures acting on the front wall of the caisson were larger than the pressures estimated by existing wave pressure formulas (Goda(1973) Formula and others) and it became about 1.5 times at maximum. Lastly, it was confirmed that overflow impingement positions to the rubble mound behind a caisson fluctuated because of the waves, which may extend damage caused by scouring over a wide range and destabilize breakwaters.