Spacing Effect on the Equilibrium Scour and Flow Pattern around Four-Pier group in Different Configurations

Present-day practices of bridge piers design often employ group arrangements of piers in various configurations to modify flow dynamics and mitigate subsequent scour formation around the piers. These group arrangement configurations may vary in aspects of spacing ratio, number of piers, and orientations to alter the flow-structure interaction, and hence the scour development. Investigating the turbulent flow behaviour around various common group arrangements has been a topic of interest for researchers for a few years now. This study presents an experimental investigation aimed at comparing the equilibrium scour depth caused by various four-pier group arrangements. To assess the impact of spacing, the face-to-face distance between piers (G) was taken to values of D, 2D, and 3D, where D refers to the diameter of the circular pier. The scour patterns reveal that the maximum scour depth occurred when spacing G was equal to D. The equilibrium scour depth decreased with an increase in the pier spacing to 2D and 3D, corresponding to an approximate flow intensity of 0.9. The scour contours exhibit the impact of neighbouring piers and how it differs with an increase in pier spacing. Instantaneous velocity data were collected to derive the flow characteristics in the flow field. Velocity vectors depict the influence of different configurations on the flow pattern. The study provides an insight into the spacing effects on equilibrium scour, which can be useful in the design of pier group arrangements.