Hydrostatic and Dynamic Pressure of Local Scour of Bridge Piers: Examination and Analysis

Scouring of bridge piers is one of the topics that is fast gaining prominence in sediment hydraulics. The collision of water flow with the pier of the bridge and its separation are the main causes of local scour around the pier of the bridge. Following the impact of water on the pier of the bridge, the pressure from the free surface of the flow toward the bed is reduced, leading to a downflow, which collides back with the mainstream, hence creating a horseshoe vortex. Horseshoe vortices are most prominent in front of the bridge pier. The separation of the current behind the pier the base of the vortex creates wake vortices. The reason for the formation of wake vortices is the increase in shear stress behind the bridge pier. Studies show that horseshoe and wake vortices are heavily involved in creating scour holes around the bridge pier. Local scouring often occurs in two modes, that is, clear-water and live bed scouring. The former is caused by the lack of advection of sediments above the bridge pier, while in the latter, the upward bed carries sediment, and the scouring hole is filled with sediments carried from the upward bed, hence reducing the depth of the scouring hole.Examination of the model simulations revealed that scouring occurs downstream of the hydraulic structures at the bridge piers, and generally, at any site where the intensity of the currents is locally heightened. The results of the study on the placement and geometric shape of bridge piers further revealed that the highest amount of scouring occurs in spindle-shaped piers compared to other forms and shapes, within which the maximum amount of scouring is witnessed in the relatively sharp edges. The simulation also revealed the amount of scouring is minimal in an arrangement in which two piers are in the front, and three piers are in the back.

Keywords:

Scouring of bridge piers , horseshoe vortex , geometric shape of bridge piers , static pressure , dynamic pressure