Investigation of Local Scour around Airfoil Shaped Pier with Collar

Methods to control and reduce local scour are based on the scour mechanism. One of these methods is the application of collar around piers and using different bridge piers geometries. In this study eight different shapes of bridge piers were used with collar around them and the obtained scour depths and rates were compared with those of circular pier. The effect of airfoil shaped piers length was also investigated. The results showed that the airfoil shaped pier with relative length of 3. 85 was more effective than the other shapes of piers due to reduction of power of horseshoe and wake vortices and the maximum scour depth reduced 22% compared to the cylinderical pier. Furthermore، using a collar with a diameter two times greater than the pier diameter in the airfoil shaped piers decreased the maximum scour depth up to 80% in comparison with circular pier and the equilibrium time of scour also increased. Also، the airfoil shaped piers which were located in flow path in inverse direction، reduced the maximum scour depth in front of pier about 60%.