Effect of spacing and skew-angle on clear-water scour at pier alignments

Pier alignments, defined as single-row pier groups, displayed normal to main bridges' axes,are frequently used to support bridge decks. Different alignments configurations, characterized by differentcombinations of piers' shape and spacing and skew-angle of the alignment to the flow direction, lead to differentinteractions with the flow field and to different scour depths.Twenty six long lasting - 7 to 15 days - laboratory experiments were run under steady clear-water flowconditions, close to the threshold condition of beginning of sediment motion, to address the effect of pierspacing and skew-angle on the equilibrium scour depth. Alignments consisted of four cylindrical piers spacedof 1, 2, 3, 4.5 and 6 pier diameters; tested skew-angles were 0◦, 15◦, 30◦, 45◦ and 90◦.The main contribution of the paper derives from the long duration of the experiments. The functional relationof issued equilibrium scour depth with pier spacing and skew-angle is established and the dependence of thetraditional group correction factor on the same variables is defined