Riprap Gradation Effect On Local Scour Around Bridge Piers

AbstractIn this paper, an experimental flume study was carried out on riprap gradation effects on local scour around bridge piers under clear water condition . Experiments were performed on circular and semi-circular piers having diameters and widths of (57, 90, 140) mm, respectively. Five mixtures of riprap were used having different gradations and the same mean grain size of (2.83) mm. The approach depth was maintained constant for all discharges which ranged between (16) l/s to (24) l/s .Experimental results indicated the importance of riprap gradation around bridge piers and that it is an important factor on its stability. Furthermore a formula for determining Froude number (Fro) at the threshold of riprap failure in terms of the variance of riprap, , the ratio between pier width to the average flow depth (b/y), and pier shape factor (k), with (R2= 0.82) was obtained.Subject headings: Scour, Riprap, Bridge piers.