Preliminary Study on the Influence of an Air-Bubble Screen on Local Scour around a Bridge Pier

Flow interactions with a bridge pier and movable river bed result in local scour which can endanger bridge pier foundations. This scour is initiated by the downward flow and amplified by the so-called horseshoe vortex. A new method to reduce scouring around bridge piers has been assessed with preliminary tests. A bubble screen located upstream of the pier may counteract the downward flow and avoid the initiation of scour. Laboratory experiments have been performed in a shallow flume with a physical scale model of a bridge pier under clear-water scour conditions. The bubble screen is generated by means of a collar linked to the pier and connected to a pressurized air system. Different water and air discharges have been tested. Vertical and horizontal location of the bubble screen have also been investigated. For each experiment, the final bed topography has been measured and compared to a reference experiment without the bubble screen. The long-term experiments (approximately 6 hours) have revealed that a well-designed bubble screen may reduce the local scour around the bridge pier.