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Abstract
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Employment of protective structures is vital for reducing the effect of the local scour created surrounding the bridge piers.
One of the most effective protective structures used for controlling and reducing scour surrounding the bridge piers is the
collars. Hence, research on the mechanism of scouring surrounding the combination of pier and collar as well as the effect
of collar on reduction of scouring surrounding the pier is of great significance. In this study, the effect of various collar
width-to-pier width ratios on reduction of scouring parameters surrounding the rectangular piers has been investigated
experimentally in various 180-degree sharp bend positions. The experiments were conducted under clear water and threshold of sediment motion in the upstream straight path. Results indicated that collars with collar width-to-pier width ratios equalto 3 to 4 perform the best at reducing the maximum depth of scouring in front of the nose of piers. Increasing the width of collar surrounding the piers reduces the maximum depth of scouring. Increasing the length of pier reduces the efficiency and effectiveness of the collar in delaying the scour process at the pier nose as well as the amount of the maximum scour reduction. The highest amount of scour depth reduction occurred in the vicinity of the pier and the collar at the 90-degree section with the collar installed with a ratio of collar width to pier width equal to 4 surrounding the piers with a ratio of length to width equal to 2 and 3 by approximately 75 and 70%, respectively
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