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Scour prediction is essential for the design of offshore foundation structures. In this study, we experimentally investigate the clear-water scour around pile groups of the circular arrangement, with uniform bed sediment and steady current. Five pile-group arrangements and two flow velocities are considered. We illustrate the scouring process around each arrangement and derive the equilibrium scour depth. Based on our experimental results as well as previously published data, we check the accuracy of three widely-used empirical methods in predicting equilibrium scour depth of pile groups. It is found that, based on the effective diameter calculated for a rectangular arrangement, the predictions of all the selected methods lead to significant overestimation. Here, we propose a new effective diameter to represent the characteristic geometry of a circular arrangement. Essentially the projected width of a pile group is calculated by the diameter of a monopile that has the same cross-sectional area of the pile group. Using the new effective diameter, the predictions from the selected empirical methods are remarkably improved. • Circular arrangement pile groups are studied through experimental investigations. • A new effective diameter is proposed to represent such foundations′characteristic. • Three empirical methods for estimating equilibrium scour depth are evaluated. [ABSTRACT FROM AUTHOR]

Wave forces on different pile-supported structures in regular and irregular waves are investigated experimentally. As a new characteristic geometric scale, an effective diameter is proposed to analyze the dimensionless total wave forces. With the effective diameter, unified empirical formulas describing the dimensionless wave forces versus Keulegan-Carpenter ( KC ) number are obtained for different complex pile-supported structures in regular and irregular waves. [ABSTRACT FROM AUTHOR]