عنوان مقاله [English]
نویسندگان [English]چکیده [English]
Local scour hole around bridge piers occurs because of flow separation and developing several vortices. Such scour hole may cause failure of the bridge especially during the river floods. In this study, the use of collars to reduce local scour at a bridge pier is presented with respect to time of scour development. This study was conducted using a 180 degree laboratory flume bend with a relative radius of Rc/B=4.67 with Plexiglas sidewalls. Tests were conducted using one pier with 60 mm diameter in the positions of 60 degree under one flow 32 lit/s and depth 12 cm under clear-water conditions. In this study, the time development of the local scour around the pier fitted with and without collar plates and four sizes of collars fitted at four elevations was studied. The soil materials used in the study had a d10 = 2 mm and geometric standard deviation 1.3. 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. So minimum depth of scour is dependent on the 3D collar and poisoned at -0.1D elevated.