Application of collar to control scouring around rectangular bridge piers

Various methods have been attempted to control scouring around bridge piers, such as using riprap, slots through the pier, a group of small piles in front of the pier, and collars. Following successful application of collars on circular piers for reduction of scouring, in this work the effectiveness of collars on rectangular piers was tested. Experiments were carried out in the threshold of sediment motion with piers aligned and skewed at 5° and 10° to the flow, and with collars of different widths and at various elevations. It was found that wider collars at lower levels are more effective and that effectiveness of collars reduces by increasing the skewness of the pier. Maximum reduction of scouring was 74, 56 and 35% for a collar with a width equal to the pier width at streambed elevation when pier was aligned, skewed at 5° and skewed at 10° to the flow respectively.