Impact of airfoil collar on scour reduction around the bridge pier

Abstract

This paper investigates the effectiveness of four different airfoil collars (bc1, bc2,bc3, and bc4) in reducing scour around the bridge pier. A total of 69 experiments are conducted under two threshold velocities with two pier diameters of 0.05 and 0.06 m and four airfoil collars placed at four locations from the uniform sediment bed. This study investigates the scour hole profiles and their depth, effect of flow intensity, collar diameter, and location on scour depth, and computes the protection efficiencies. The results show that the collar effectively reduces the scour depth. When the collar is located at bed level (i.e., y = 0, where y is water depth from the bed), y/4, y/2, and 3 y/4 above the bed level, the protection efficacies are found to be ranging between the percentages 65–100%, 40–53%, 23–38%, and 8–29% for bc1, bc2,bc3, and bc4, respectively. An empirical relationship is proposed for variation of scour depth with respect to time. Statistical sensitivity analyses are performed and found that the most and least sensitive parameters are h/y and Tc, where h and Tc are the collar's location from the water surface and dimensionless time, respectively.