Experimental investigation of current-induced local scour around composite bucket foundation in silty sand

In recent years, local scour has received attention because it may have a negative effect on coastal structures. Because of the large-scale arc transition and other special constructs, flow patterns around composite bucket foundation are complicated, and the local scour around composite bucket foundation has rarely been reported in the literature. In the present study, a detailed laboratory testing program on model with diameters of 150 cm and 75 cm embedded in silty sand was conducted in a flume. The scouring process and equilibrium scour hole geometry under steady and bidirectional current were investigated in detail. A procedure was suggested to predict the ultimate scour depth based on the observed variation of the scour depth over a limited time period. The equilibrium scour depth under a bidirectional current was approximately 16% less than that under a steady current, and there were two spoon-shaped scour holes in the steady current scour, whereas four saddle-shaped scour holes were discovered in bidirectional current scour. Based on these results, a functional relationship was suggested between the scour depth and other parameters, such as the diameter of the foundation, Shields parameter and median diameter of the soil bed. (C) 2016 Elsevier Ltd. All rights reserved.