Parametric study for hydraulic design of air-bubble injections to control scour around circular bridge piers

Several countermeasure techniques have been presented to control bridge scour-induced failure. Air-bubble injection, a new method compatible with the environment, was introduced to combat destructive vortices that cause bridge piers to be scoured. Extensive experiments were conducted to determine the appropriate air-bubble injections for the least scours at a bridge pier. Two different clear-water flow intensities with air-bubble injections were assessed in different radial positions around and also on the upstream half of the bridge pier. The vertical position of air injections and air discharge were determined previously to be optimal. The long-term experiments revealed that the well-designed air-bubble injections reduced the local scour around the bridge pier. It was found that the complete air-bubble injection around the bridge pier is the best configuration and able to reduce the scour depth about 44% over the case with no air injection (non-protected pier). Moreover, the appropriate arrangement of bubble injections to lessen the scour depth is the nearest radial position of the injection to the bridge pier and with increasing the radial distance of injections to the pier, the bubble plumes move downstream by the main flow. The results indicate that bubble plumes would be effective in both flow intensity, u*/u*c = 0.7 and 0.9, as examined in the present study. © 2022 Indian Society for Hydraulics.