Wave scour around group of vertical piles

The paper presents the results of an experimental investigation on scour around pile groups with different configurations exposed to waves. Two kinds of tests were carried out: the actual scour experiments, and bed shear stress measurements. Seven kinds of pile-group arrangements were tested, including the side-by-side arrangements of piles, tandem arrangements of piles, and triangular and square group arrangements with two-, three-, and four-pile groups, The variations with the pile spacing as well as the Keulegan-Carpenter number, KC, were investigated. The scour depth can increase with respect to its single-pile value by as much as a factor of 3 for moderate KC numbers [such as O(10)] for most of the pile-group configurations for small pile spacings. For small KC numbers, this increase can be even higher, by as much as a factor of 10 or more. For a given pile spacing, the scour depth is mainly governed by the KC number. In agreement with the single-pile case, the larger the KC number, the larger the scour depth. The bed was live in all the tests except a few cases.