Effects of Six-Leg Elements Row Quantity on Reduction of Cubic Bridge Pier Scour Depth

The six-leg elements with trade name of A-jack frequently have been used in coastal structures and recently have been recommended as an effective tool for controlling river bank erosion. The purpose of this study was to investigate the applicability of such elements in reduction of scour depth at bridge piers. Therefore, two series of tests without and with the mentioned elements in three different quantities of rows were carried out. Five different flow conditions, with Froude number in the range of 0.16 to 0.24 around the cubic bridge pier, were performed and bed topography was measured in all experiments.The results of this study show that for Froude number of 0.16, the six-leg elements can reduce the maximum scour depth by as much as 44%, 83% and 100% when the elements are placed in single row, in two rows and in three rows, respectively. The increase of Froude number causes reduction of the effect of six-leg elements on scour depth. So, for Froude number equal to 0.24, the above-mentioned percentages of maximum scour depth reductions were found to be 44%, 63% and 81%.