Experimental Investigation of the Bed Sill Effect on the Temporal Evolution of Local Scour Hole around an Inclined Pier Group on a Foundation

One of the vital structures in the land transportation cycle is the bridge. Constructing this structure over the rivers results in an intensified 3-D flow pattern around piers which in turn causes the bed sediments to be eroded and scoured from the immediate vicinity of the pier and its foundation. It is likely that the bridge will fail particularly during a high flood event, if the foundations or piles are not constructed deep enough. Hence, besides the previous works on the study of the factors affecting scour at bridge piers, considering appropriate countermeasures against bridge scour is of primary importance. In the present study, the effect of bed sill location on the temporal evolution of the scour around an inclined pier group was experimentally investigated under various hydraulic conditions and foundation levels. A physical model of pier group with two inclined 2.5x3.5 cm rectangular piers and 28 degree inclination angle constructed on a 10x16 cm foundation was considered in the experiments. The experiments were carried out with different locations of sill (front, middle, and rear of the foundation), various flow velocities and depths, and normalized installation levels of the foundation (distance of the top of the foundation to the bed surface normalized by the pier width) equal to -1.0, -0.5, 0.0, and +1.0. The results of the present study indicate that the bed sill location has a significant effect on the temporal evolution of the depth of scour hole. Based on the comparisons made in this study, it is found that the installation of the sill in front of the foundation has a better performance in the scour mitigation rather than other arrangements. It is also concluded that the average reduction in the scour depth in all foundation installation levels is equal to 22, 18, and 15 percent for front, middle, and rear sill configurations, respectively.