Reduction of local scour at a bridge pier using collar in a 180 degree flume bend

In this study, the use of collars for reducing the effects of local scour at a bridge pier is presented together with the time aspect of the scour development. The adoption of a collar is based on the concept that its existence will sufficiently inhibit and/or deflect the local scour mechanisms so as to reduce the local scour immediately adjacent to the pier. The overall objective of the research is to study the temporal development of the scour for a pier fitted with a collar and a pier without a collar. The study was conducted using in a 180 degree laboratory flume bend with a relative radius of R/B = 4.67 operated under clear-water conditions. The median size and geometric standard deviation of bed material were equal to d50 = 2 mm and sg = 1.7, respectively. Tests were conducted using one pier with 60 mm diameter in positions of 60 degree under one flow conditions. In this study, the time development of the local scour around the abutment fitted with and without collar plates was studied. The effects of various sizes of collars fitted at different elevations on the temporal development of scour depth at the abutment were also studied. The time development of the scour hole around the model pier with and without a collar installed was compared with similar studies on bridge piers. The results of the model study indicated that the maximum depth of scour is highly dependent on the experimental duration. It was observed that, as the size of a collar plate increases, the scour decreases. The minimum depth of scour occurs for the collar at diameter of 3D placed at elevation of -0.1 D from the bed surface. © 2010 Asian Network for Scientific Information.