Influence of flow conditions on scour hole shape for pier groups

Local scour at alluvial bridge foundations is caused by the interference of the flow with the structure. The usual laboratory experiments set constant flow conditions and allow local scour to develop until the equilibrium stage, which can take several days. However, as long as the geometry of the scour hole is independent of the flow conditions used to obtain a given scour depth, faster experimental methods are available in the literature. In this paper the influence of flow conditions on the shape of the scour hole is investigated experimentally for different configurations of pile groups with and without pile cap. It is found that, whenever no pile cap is present, the angle of repose of the sediment dominates the geometry of the scour hole, regardless of flow conditions. On the contrary, in the presence of a pile cap, the geometry of the scour hole strongly depends on flow conditions.