Test of Scour Protection for Bridge Piers

If flood velocities concentrated by the area constriction at bridges remove material from under the bridge pier foundations, the pier may settle or collapse. The maximum depth of scour occurring during the passage of a flood peak is difficult to ascertain or to estimate by empirical formulas or model tests. To explore further the method of limiting the depth of scour by surrounding the pier with protective material, model tests were made covering a range of constriction percentages, depths of flow, and Froude numbers, using both round and elongated piers. After determining the extent of the scour hole formed during the passage of a simulated flood, the protection afforded by a layer of protective material was tested with a repetition of the same flood. If the material of the layer was large enough to resist being moved and had a grain-size distribution capable of preventing leaching, no scour hole formed. A special test showed protection remaining intact despite stream bed degradation.