An experimental study of live-bed scour at circular pier in covered flow

Live-bed scour at a bridge pier in covered flow was experimentally investigated. The laboratory campaign also comprehended a clear-water run and preliminary tests (without the pier) that were performed to characterize the pattern of the bed-forms developing in the channel. Fixed-point measurements of the bed elevation were obtained for all the runs with a laser distance sensor. The maximum scour depth and the equilibrium time decreased for increasing flow velocity; these results are in agreement with the typical depictions of the process for open-channel flows. It must be however noted that equilibrium conditions were not achieved in the clear-water run. An analysis of the dune properties (length, height) was performed based on the results of the preliminary tests, and a comparison with literature predictors showed variable levels of agreement. The fluctuations of the scour depth after equilibrium were compared to the oscillations of the bed elevation related with the bedforms. Additional experiments in different conditions and with longer duration are presently under design.