A Novel Collar Design to Mitigate Bridge Pier Scour

The study presented herein will introduce an alternative bridge pier scour countermeasure, in the form of a novel three-dimensional collar, which will reduce or eliminate the harmful scour around the base of the pier. Bridge pier scour, which is the erosion of riverbed material from around the base of bridge piers, is one of the leading causes of bridge failure. Scour is caused by the flow separating around the bridge pier. As the approaching flow impacts the upstream face of the pier, a portion is redirected downwards to the riverbed where it forms a vortex. This vortex continues to develop around the upstream face and sides of the pier, in the shape of a horseshoe, eroding the riverbed material from around the base of the pier. The remainder of the approaching flow that is influenced by the pier, but is not redirected down to the riverbed, experiences an increase in velocity as it bypasses the pier, resulting in further scouring along the sides of the pier. The combination of these scour causing sources not only jeopardizes the structural integrity of the bridge, but also puts the public’s safety at risk. Various countermeasures are available to help mitigate this issue; however, there is not one that is easy to install, nonintrusive, maintenance free, and cost effective, in addition to eliminating or greatly reducing scour.

This novel collar will be mounted around the base of the bridge pier and will rest directly on the riverbed. This collar design was developed to contain the horseshoe vortex that forms on the front and sides of the pier and direct it safely in the downstream direction. By doing so, the collar prevents the horseshoe vortex from contacting the riverbed, eliminating therefore one of the main scour-causing mechanisms. In addition, the collar shields the riverbed around the pier from the localized accelerated flow, thus helping to avoid the other main scour-causing mechanism. However, the flow exiting off of the collar induces a small degree of localized scour. Upon further optimization, this new collar design has the potential to greatly improve the way pier scour is currently addressed, as it combines easy installation, minimal maintenance, small environmental impact, low cost, and scour reducing capabilities. The paper will present the results of a comprehensive experimental and numerical program for the design of this collar.