Local Scour Around Bridge Piers

TLDR

Local scour around bridge piers is driven by the horseshoe vortex system at the pier base, with blunt‑nosed piers generating a strong pressure field, and the sediment transport conditions determine whether the scour is clear‑water or involves continuous sediment motion. The study proposes design criteria for blunt‑nosed piers in clear‑water and continuous‑sediment scour. The authors discuss deviations from ideal design conditions and suggest alternative design methods for such cases. Findings show that the pier Reynolds number governs horseshoe vortex strength, and that equilibrium scour depth depends on the initial sediment transport condition under steady uniform flow with fully developed bed material transport.

Abstract

Local scour caused by the horseshoe vortex system which forms at the base of the piers is considered. Piers which induce a pressure field strong enough to cause the formulation of the horseshoe vortex system are termed blunt nosed; all others being classed as sharp-nosed piers. The condition of the sediment transported into and out of the scour hole forms the basis for the further classification of the scour process into clear-water scour and scour with continuous sediment motion. The pier Reynolds number is shown to be an important variable describing the strength of the horseshoe vortex system. Further, the equilibrium scour depth depends on the initial sediment transport condition for a steady uniform flow with fully developed bed material transport. Design criteria are proposed for blunt-nosed piers under the conditions of clear-water scour and scour with continuous sediment motion. Several deviations from the above ideal design conditions are discussed; methods for design in these cases are suggested.