Study on the Effect of Installation Depth of Pipe on Scour Depth Under the River Crossing Pipeline in Unsteady Flow

Water and other fluid pipes that are placed on the seabed and rivers bed change the flow pattern around them. These changes increase the shear stress of the bed and the severity of turbulence around the pipe and create a scouring hole under the pipe. The scouring under the pipe may lead to instability, bending, and even breakage of the pipeline. In this study, local scouring around pipelines across the river in unsteady flow conditions was investigated. In the experiments, three pipe diameters (20, 40, and 60 mm) and three installation depths (on the bed, a quarter of the pipe diameter above the bed, and half of the pipe diameter above the bed) were used. It can be understood from the results of this laboratory study that the amount of final scour depth due to the passage of flood hydrograph is always less than the scour depth due to the steady flow corresponding to the peak flow of the hydrograph. For different pipe installation depths, the amount of scouring for the installation depth of onequarter of the pipe diameter above the bed in both steady and unsteady flow conditions is higher than other installation depths.