Abstract: The change in riverbed morphology and the reduction of bridge pier foundation's buried depth resulted from local scour around the pier are major causes of bridge failure. An all-time and all-round 3D numerical simulation on the flow scour around the foundation of bridge pier is carried out by using LES (Large Eddy Simulation) in association with the equation of flow motion and the theory of sediment dynamics. The streamlines of eddy flow around the bridge pier foundation and the contours of riverbed elevation were acquired. The effects of flow velocity and median particle size on local scour around bridge pier were examined. The numerical simulation results suggest that the depth of the scour pit increases with the increase of the initial flow velocity and the formation of scour pit accelerates in the meantime. Scour pit depth also extends with the reduction of riverbed's median particle size; but when the median particle size is small to a certain extent, the depth of scour pit shrinks because of the increasing of cohesion between sediment particles.

Key words: scour around bridge pier, large eddy simulation, flow velocity, depth of scour pit, median particle size