A laboratory study of the effect of asymmetric-lattice collar shape and placement on scour depth and flow pattern around a bridge pier

Abstract

In this study, the effect of collar shape and alignment on reducing scour depth at the front part of a bridge pier, under clear water conditions, was investigated to determine changes in the flow pattern around the structure. Collars were examined in two asymmetrical shapes with dimensions of (3 × 4) and (3 × 6) at three levels of installation relative to the bed: At bed level itself, and at 1 and 2 cm above the bed. The results revealed that the presence of the collar not only reduced the ultimate scouring depth but also delayed the formation of the scouring hole. This impact was observed to be greater as the size of the collar increased. In addition, lowering the alignment of the collars can lead to their better performance and efficiency in the cost of the design. Therefore, collars installed on the bed surface indicated good performance in controlling scour. On the other hand, once the flow characteristics around the bridge pier with and without collar were examined, it was determined that affecting the downstream flow reduces the strength of the vortices and changes the reciprocating behavior and the displacement of the vortices.