Experimental Investigation of Local Scour Around Conical Pier

There are many reports about failure of bridges around the world due to scouring. This shows the importance of research on scouring and any possibility on scour protection. The method used of control of scouring around the bridge piers can be divided in two categories, namely: Direct and Indirect methods. The first method may be done by increasing the streambed resistance. This is usually done by riprap around piers. Indirect control, however, can be achieved by changing the flow pattern around a pier. The second method can be done for instance by using a collar around the pier or using a slot within the pier. Another method of the second category is to use variable section in depth. For this purpose, various slopes of conical piers are investigated in this research study. Experiments were carried out in a channel with 10 meters long, 0.3 meter wide and 0.5 meter depth, having a horizontal slope. Median size of sediment was 0.78 mm with geometric standard deviation of 1.24. The experimental results have been shown that the scour depth at conical piers decrease in compare with cylindrical ones. These observations, may partly be due to decrease in bed shear stress, which is a key parameter for the sediment transport. Therefore, from experimental data it was found that with a very mild slope on conical pier, the scour depth decreased about 15.8% when compared with the cylindrical one. For the other piers with larger slope and larger diameter on the bed, the wall side effects were appeared, however the reduction rate of scour depth was not as much as expected, compared with the first conical pier.