Experimental Study of Local Scour around Twin Piles in Oscillatory Flows

Abstract

Laboratory experiments have been carried out to investigate the scour around single piles and twin-pile groups subject to oscillatory flows. The Keulegan-Carpenter number, which is proportional to the ratio between the maximum excursion of water particles and the pile diameter, ranges from 3 to 110 in the experiments. To verify the experimental setup, the scour around a tall monopile was first studied, and the results were found to agree well with the previous research. The effect of the pile height and the influence of the twin-pile layout on the scour have been subsequently investigated. It was found that the scour became independent of the pile height once the pile was four times higher than the diameter. An empirical expression was constructed to describe the exponential variation of the scour depth with the pile height. The individual piles in a twin-pile group were found to behave independently when the separation was three times greater than the pile diameter. The relationships between the scour depths around the twin-pile groups and the group configuration were established graphically.