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 its alignment on reducing scour depth in the front part of the structure, with the pier under clear water conditions, was investigated to determine changes in the flow pattern around the structure. The collars were examined in two asymmetrical shapes with dimensions of and at three levels of installation relative to the bed: bed level, 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, reducing the alignment of the collars can lead to better performance of the collar and its 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.

Characteristics of reducing local scour around cylindrical pier using a horn-shaped collar

“…Compared with a circular collar, a rectangular collar has better protection to the sediment surface; it reduces maximum scour depth around piers by 79%. Raeisi and Ghomeshi [16] proposed an elliptical collar to weaken the downstream vortex through interference on the water flow downstream of the bridge pier, which has better performance than the ordinary circular collar. For the three-dimensional collar, Bestawy et al [17] developed a conical collar, which was found to have a good effect on reducing scour around the pier through a single pier model experiment, and the scour depth downstream side of the pier was reduced by 61.1%.…”