Effects of Footing Location on Bridge Pier Scour

A laboratory study was conducted to investigate the effects of footing location on the depth of scour. None of the existing pier‐scour equations have provisions for accounting for nonuniform pier configurations; rather they have a single characteristic pier dimension. This study was aimed at evaluating various techniques for characterizing the effective dimensions for a pier/footing combination when both are exposed to the flow field. The following three techniques were considered in the analysis: (f) Use of the footing width as the characteristic dimension when the footing occupies more than 10% of the flow depth; otherwise, use of the pier width (10% depth switch); (2) use of a weighted pier width (weighted width technique); and (3) use of the dominant pier/footing component by making two computations with appropriate flow parameters and selecting the larger value (dominant component technique). The first technique was the Federal Highway Administration (FHWA) recommended procedure prior to this study, but both of the other techniques gave better results in this study. The third technique has subsequently been adopted for FHWA's Hydraulic Engineering Circular No. 18 (HEC‐18) on bridge scour. The second technique, however, is a simpler technique and is as accurate.