Riprap Protection without Filter Layers

Conventional multilayered riprap and filter protections around bridge piers can be substituted by one thick single layer of riprap. Because of this simpler construction, field installations are less likely to be defective. An analytical description was derived relating the mean flow velocity, which causes initiation of erosion of the base material, to characteristics of the single‐layer protection and the base material. The governing dimensionless parameters describe suitable thickness of the riprap layer, grain size of riprap material, grain size of base material, and mean flow velocity. The diameter of the pier does not influence initiation of erosion. The theoretical expression was verified by means of comparative largescale laboratory experiments. In most design conditions the simplified riprap protection requires a thinner protective layer than the conventional riprap and filter protection.