An Experimental Study of Characteristics of Solitary-Wave-Induced Scour Around a Pile Breakwater with a Discussion on Effects of the Distance Between Piles

Understanding tsunami-induced scour at a pile breakwater is important for the foundation safety of this type of coastal defense structures. A series of wave-flume tests were performed for G/D = 0.11, with G being the gap size and D the pile diameter, to study the characteristics of the solitary-wave-induced local scour around a pile breakwater, including the scour-hole depth, scour-hole length, deposition sandbar height and the scoured volume. It was found that the jet flow through the gaps between piles caused the local scour around individual piles. A more or less two-dimensional deposition sandbar was found on the down-wave side of the pile breakwater in the later stage of the scour process. A new empirical equation was introduced to approximate the evolution of the depth of the scour hole induced by a series of solitary waves. The equation was verified by existing data reported in the literature for G/D = 0.39 and the new data reported in this study. Effects of the distance between piles on the characteristics of the local scour were discussed by comparing the results for G/D = 0.11 and 0.39. The comparison showed that the scour-hole depth and height of the sandbar for G/D = 0.11 were all noticeably larger than the corresponding values for G/D = 0.39.