» Research Note «Experimental investigation of scour pattern around the group of three divergent-vertical and convergent-vertical bridge piers in a 180 degree sharp bend

Most of the rivers have meandering shape in plan view. By embedding bridge piers in the river, a series of vortices establish in the flow. These vortices are the main cause of pier scour, which gradually led to formation of scour hole around the piers. Todays, the local scour is known as the main cause of bridge destruction around the world. Since the meandering rivers are the most common type of rivers in the plan, in this paper the scour processes are studied around a group of three divergent-vertical and convergent-vertical piers located at the 180 degree bend, in both cases of streamwise and transverse layouts. The experiments were conducted in a 180 degree sharp bend channel (with a ratio of central curvature radius to width of channel equal to 2) in initial sedimentary bed conditions with particle mean diameter of 1.5 mm. The results showed that in both cases of three convergent-vertical and three divergent-vertical groups-piers embedded in the flow direction, the scour around the first inclined pier and the second vertical pier reached to same value. Furthermore, the bed changes in transverse direction was more than the flow direction. In the transverse layout, it was observed that the maximum depth of scour hole near the convergent-vertical group piers was 20% more than the divergent-vertical group piers.