Research Note «Experimental Investigation on Local Scour around Conical and Pyramidal Piers

The present study was conducted to investigate the use of conical and pyramidal piers in reducing local scour risk at the bridge piers. The efficacy of different diameters on the bed and water surface (i. e. different lateral structural slopes of piers ranging from 1:60 to 1:10) with constant projected areas was studied. The experimental results for the two flow intensities (velocity of flow to critical velocity of flow) of 0. 92 and 0. 86 showed that the scour depth in bridges with conical or pyramidal piers decreased significantly in comparison to those with cylindrical and cubical piers. For the flow intensity of 0. 92، it was found from the experimental data that by making a very mild slope (1:60) in conical piers، the absolute (maximum measured depth of scour) and relative (ratio of maximum measured depth of scour to diameter on the bed) scour depths were reduced about 15. 8% and 25. 1%، respectively when compared to the cylindrical one. For the same conditions in pyramidal piers، the absolute and relative scour depths were reduced about 8. 9% and 18. 4%، respectively، in comparison with the cubical one. In the case of other piers with steeper slopes and consequently larger diameters on the bed، in spite of considering the same criteria، the side walls and wake vortex behind the pier altered the process of experiments and therefore the reduction rat