Effect of relative sediment size on clear-water equilibrium scour depth at single cylindrical piers

摘要

Experiments on local scouring around cylindrical piers were performed in steady clear-water conditions to investigate the effect of sediment size, D_(50), on equilibrium scour depth, d_(se). Thirteen experiments, run for 7 to 13 days, were carried out. The dependence of the normalized equilibrium scour depth, d_(se)/D_p, on the relative sediment size, D_p/D_(50), was identified, corroborating the findings of Sheppard et al. (1995; 1999; 2004). Contrarily to consecrated literature and associated practice, it was observed that the normalized equilibrium scour depth decreases with the relative sediment size, for D_p/D_(50) > ~100. This effect is possibly one of the causes of frequently reported over-prediction of scour by formulas established on the basis of laboratory studies, where frequently D_p/D_(50) < ~100.