Aspects of Downstream Bed Sill Location for Investigating the Countermeasure with Local Scour around Cylindrical Bridge Piers

ABSTRACT The countermeasures versus local scour around bridge piers are essential for safe bridge hydraulic design. In this study, laboratory experiments were conducted to investigate the effectiveness of downstream bed sill location as countermeasure method to decrease the local scour under clear water conditions for single cylindrical pier. Four flow intensities were tested (from 0.48 to 0.96 of the threshold velocity of sediment) with five different bed sill locations (from 0 to 4 pier diameter). The measured scour depths were compared with that observed at the exposed pier (four tests for unprotected pier) to estimate the percentage reduction in scour depth for each flow intensity and to assess the aspects of bed sill location. The results revealed a significant effect of bed sill location on decreasing the scour depth with in downstream distance equal to pier diameter. Accordingly, the percentage decrease in scour depth was ranged from 4 to 30%. New empirical formula has been proposed to estimate scour depth near circular bridge piers according to different bed sill configuration. Graphical abstract