Clear-Water Local Scour at Skewed Complex Bridge Piers

AbstractAn experimental study on flow-induced clear-water local scour at complex bridge piers was conducted using two typical pier models, nine pile-cap elevations, and seven pier skew angles from 0° to 90° with a 15° interval. Results show that a slight skew angle α imposed on an originally aligned pier can significantly increase the equilibrium scour depth dse. When a pier was skewed to the flow, the column made the largest contribution to the scour depth because its wide-pier feature became dominant. Three categories of the pier skewness were defined, namely, an aligned pier (= 0°), a slightly skewed pier (α≈15°), and a highly skewed pier (α≥30°). The influences of the pile cap and the pile group on the scouring process were weakened with increasing α. Additionally, for highly skewed piers with fully submerged pile cap, the equilibrium scour holes tended to equally expose the pier components, no matter the location of the undisturbed bed level. A new scour prediction method is presented, involving modifications for the effect of sediment coarseness. The new method leads to a higher safety margin with significantly reduced underestimation.