Effect of Bridge Pier Shape on Depth of Scour

Abstract

Scour at bridge piers is a common problem in infrastructure engineering, as local scour around bridge piers is one of the most common causes of bridge failure. Prediction of the maximum depth of local scour thus plays an important role in ensuring safety and economy during design and maintenance. A computational fluid dynamics (CFD)-based simulation methodology for computing the depth of local scour around bridge piers using Flow-3D model is thus proposed in this study. The objective is to investigate the effects of the bridge pier shape on local scour in order to develop an optimal hydraulic design for minimum depth of scour. Local scouring around different shapes of pier (circular, rectangular, square, octagonal, elliptic, and lenticular) in non-cohesive bed sediment under clear water scour conditions was thus simulated for each pier shape at different of flow intensities, fluid depths, and pier sizes. By comparing the numerical results for predicted scour depth around a circular pier with the laboratory experimental results produced by Melville in 1975, the model was found to have about a 10% error rate for prediction of scour depth, demonstrating good agreement with experimental models. The model results revealed that the rectangular pier shape recorded the maximum depth of scour, while the minimum depth of scour was measured for the lenticular shape, this being about 40% lower than for other shapes. All factors investigated were found to have direct effect on scour but the most significant factor was pier width; scour reached its maximum depth value at pier width ratios of 0.2 in rectangular pier shapes; the results also showed that scour depth was comparatively higher upstream and lower downstream. Overall, the proposed numerical simulation Flow-3D method is a reliable tool for predicting and generating discussion of spatial influences on the bridge scour process.