The effect of Pile Cap's Shape at Scour Hole Dimensions at Bridges with Composite Geometry

Local scour around bridge piers is the most common reason for bridge failures. many bridges have fractured because the lack of attention to the importance of hydraulic factors every year. Despite extensive researches on local scour, there is no precise method for predicting scouring because of the complexity of the scour mechanism, especially in bridges with complex piers. In this research the effect of pile cap's shape on the scour hole dimensions was investigated by using physical simulation. Laboratory data were extracted of three scaled down models of complex piers with different pile cape's shape. The experiments were conducted in clear water conditions with uniform sediment and constant discharge. The models were made with an appropriate scale from real piers of bridges. During experiments water depth was kept constant and it provided shallow water depth condition. The variation of scour hole's length, width and depth was recorded. A 3D illustration of the model for each experiment was drawn. The length, width and depth of the scour hole coordinates were measured in three directions. The results illustrated that the length and width of the scour hole, the same as depth, are also significantly dependent on the shape of the pile cap and its elevation. Results showed that The maximum length, width and depth of the scour hole were,11lpc, 8.5bpc and 9T respectively. These results can be used by engineers and researchers in order to attain at a pattern for predicting the dimensions of the scour hole in the complex bridge piers.