Experimental study of scour around pile groups in steady flows

This paper presents comprehensive experimental results of scour around pile groups with different pile arrangements under different steady flow conditions, with the main aim of analyzing the influence of pile spacing (G/D) and Froude number (Fr). The temporal developments of scour depth measured at different positions around different piles are provided and yield exponential functions. The temporal variations of scour depth at the front pile and the rear pile are significantly different for small values of Fr. The equilibrium scour depth of pile groups decreases with G/D, and the scour depth at the rear pile is apparently smaller than that at the front pile. The critical value of G/D representing the pile group effect tends to increase with Fr. The equilibrium scour topography is divided into local scour at individual pile and global scour over entire area of pile group, and the local scour is less obvious with the increase of Fr. Additionally, the results of scour hole dimensions show that the length of the scour hole upstream of the pile group decreases with G/D while the width of the scour hole increases slightly with G/D. Finally, empirical relationships are obtained to predict the equilibrium scour hole area and volume.