Determination of Optimum Depth and Dimensions of Roughening Elements on Bridge Abutment as Scour Countermeasures

In the recent years, the failure of many bridges has reported due to local scour around abutment. Many studies have focused on reducing the scour with the help of structures reducing the destructive effects of flow. In this study, the scouring effect on two vertical wall abutments with different widths was investigated using clean water. Where the upstream face of the latter is protected with roughening elements as devices to intercept the down flow responsible for the formation of the principal vortex. Different sizes of the elements with thicknesses and protrusions equal to 0.025L, 0.05L, 0.1L, 0.2L and 0.3L (L is the length of the abutment) placed at different elevations on abutments were investigated. The optimum elevation of roughening elements obtained at 0.6L below the bed level. As the thickness and protrusion dimensions of the elements increases to 0.2L, scour depth around the abutment decreases, and after that increases if the element size become larger. In conclusion, the roughening elements with thickness and protrusion equal to 0.2L and placement of 0.6L below the sediment bed reduced the scour depth 30.4 and 32.8% at the small and large abutments, respectively.