Scour at Cylindrical Bridge Piers in Armored Beds

Results of laboratory experiments concerning the development of scour around a cylindrical pier placed in a bed of cohesionless sediment overlain by an armoring layer of coarser sediment are presented. Both the armoring layer and the bed beneath it were composed of uniform‐sized sediment. It was found that, under these conditions, the depth of scour at a pier may exceed that which occurs at a pier in a nonarmored bed. Local scour due to the local flow structure around a pier may either develop through the armor layer and into the finer, more erodible, sediment, or it may trigger a more extensive localized scour of the bed sediment exposed to the flow by the erosion of the armor layer. Design formulas to estimate the maximum equilibrium depths of scour are proposed.