Live-Bed Scour at Wide and Long-Skewed Bridge Piers in Comparatively Shallow Water

Abstract

An investigation of the characteristics of live-bed scour at circular and skewed rectangular (slab) piers in comparatively shallow flows is presented. The 110 experiments were undertaken in a 2.4-m flume using two circular piers and a slab (long) pier. Based on flow shallowness, that is, the ratio of approaching flow depth (y0) to pier diameter (D), the new data span the wide-pier (y0/D<0.2) and transition-pier (0.2≤y0/D<1.4) scour ranges. The Sheppard-Melville (S-M) method shows better performance than the other existing predictors and is more readily modified. Modification to the equation for the flow shallowness factor in the S-M method is proposed, based on both the data from the present study and those from literature. The results show the considerable influence of flow shallowness ratio on scour depth at piers in comparatively shallow water, and that, even for non–ripple-forming sediment, the scour depth at the live-bed peak may still exceed that at the clear-water threshold. The modified predictor provides better accuracy than the original Sheppard-Melville method for piers with y0/D<1, and no significant underestimation of the maximum scour depth is observed.