Study of Collar Effect on Scour Reduction around Vertical Semicircular Bridge Abutments

Bridge abutments cause constriction in river section and change the pattern of river flow. Due to presence of a bridge abutment in a river the velocity and bed shear stress increase, vortices are formed and finally local scouring around structure commences and as a result a scour hole develops. In order to reduce scouring around bridge abutments one method is to set the collar. Collar by deflecting the down flow mitigate scour and produce a time delay in scour hole development process. Hence in this research the effect of collar on scour reduction around vertical semicircular bridge abutments was experimentally investigated. Experiments were conducted in the flume with 6 m long and 0.8 m wide under clear water condition (i.e. = 0.85). The results showed that collars reduced the scour depth significantly, and 63.5 to 100 percent reduction on the scour depth and delay on the time of scouring were observed using different collars. Maximum scour depth also moved downstream of the bridge abutment.