Effect of Netted Collar on Cubic Bridge Pile Groups on the Maximum Local Scour Depth

Every year by flooding in various parts of the world a large number of bridges are destroyed just when its need to used widely. Most of this bridge destruction are due to scour around their piers. Erosion and the movement of the bed materials due to water flow is called scour. During this process, a hole is developed around piers and progress to reach to a depth of equilibrium gradually. For this research a laboratory flume with 6m length and width of 73cm located in the hydraulic laboratory of the Shahid Chamran University of Ahvaz was used. In order to reduce the scour around pile groups a flat plate with small thickness called collar are installed around the middle set of the pile groups. The collars used were netted with four percent
0% (simple collar) of 30%, 50% and 70% and they were installed in three levels, on the bed, 0.5D and 1D above the bed. The experiments were conducted under clear water condition and three Froude Number were equal to 0.12, 0.14 and 0.16 and the results were compared with the case of piers without collar. The results showed the simple collar located on the bed and netted collar with 70% of opening located on the level of 0.5D relative to the bed surface in both cases the reduction of scour in the front pier were equal to 86 percent compared to non-collar and these cases had the highest performance