Experimental Study on the Effect of Thickness and Level of the Collar on the Scour Pattern in 180° Sharp Bend with Bridge Pier

Scouring around the bridge's piers is one of the major causes of serious damage to the bridge pier. A laboratory modelling method has been utilized in this research to study the effect of level and thickness of collar on scouring around the pier. The experiments were carried out in a channel with a 180° bend and a relative curvature radius equal to 2. This channel is composed by the straight upstream- and downstream-directed paths, respectively, 6.5 and 5.1 m long and 1 m wide. All experiments were conducted with a constant discharge capacity equal to 0.07 m3⁄s. The obtained results indicated that the installation of the collar at the initial bed surface and 0.4 pier width under the initial bed level with thickness of 0.12 and 0.06 pier width helped gain the best results in reducing the amount of scouring when placing the pier at 90° of the bend. It also decreased 70% of the maximum depth of the scour hole in comparison with when the collar was not implemented. In the positions of 60° and 120°, the thickness parameter has no appreciable effect on scouring, and the best level of collar in this positions is same as the pier located at 90° of bend.