Time Variations of Scour Below Submerged Skewed Pipelines

Abstract

The presence of pipe across river initiates the piping effect combined with the stagnation eddy and vortex system in the vicinity of the pipeline. The main objective of the research is to investigate the physics of scour below skewed pipeline in river crossing as well as the time variations of the scour development. In this study, the experiments were conducted for four different angles of pipe (30°, 45°, 60° and 90°) across a channel and placed on the sediment bed with e/D = 0. The scour development for flow shallowness y/D = 3 and y/D = 4, initiated at downstream side of the pipe, where the bed sediment appeared to be ejected from the bed due to the piping effect process. At the initial stage, the scour process for 150mm flow depth enlarged rapidly. Whilst, the scour process for 200 mm flow depth slowly developed and after certain time, the sediment bed scoured rapidly. The scour depth increased considerably at development stage and the suspended load near the bed especially below the pipe decreased significantly compared to the initial stage. The rate of sediment eroded from the sediment bed decreased at the stabilization phase. The equilibrium phase of the scour depth considered achieved as the dimensions of the scour hole do not change significantly.