Influence of Sacrificial Piles on Scour Reduction of Cylindrical Bridge Pier

Local scour around a bridge pier results from the flow and pier interaction and separation of the flow at the sides of the pier. One of the methods for a local scour countermeasure at bridge piers is the use of sacrificial piles. Sacrificial are piles placed upstream of a bridge pier for the purpose of protecting it from local scour by deflecting the high-velocity flow and reducing vortex system behind them. In this paper the effects of pile size and spacing between sacrificial piles are investigated in an experimental flume under clear-water condition. Uniform bed sediment with a median diameter of 0.5 mm was used. The cylindrical pier was 40 mm in diameter (D). The sacrificial piles were of 32, 27 and 20 mm diameters (d) and the distances of the first sacrificial pile were equal to 2.8D, 2.95D, 3.1D and 3.4D from the upstream face of the pier. Three different flow rates were used, identified by V/Vc equal to 0.67, 0.81 and 0.94. The results show that increasing flow intensity reduces the sheltering effect of the pile group. Also up to optimum distance, increasing the sacrificial pile diameter improves the effect of these piles, but for larger distances of the sacrificial piles the most efficient scour reduction occurs for the smallest sacrificial piles diameter. Furthermore, the experimental results show that when the sacrificial pile is located at a distance equal to 2.95D of pier (X), the significant scour reduction nearly to 39 - 121% will occur.