EXPERIMENTAL STUDY ON LOCAL SCOUR OF SANDY SEABED UNDER SUBMARINE PIPELINE IN UNIDIRECTIONAL CURRENTS

The similarity rules for modeling local scour of the under submarine pipeline are established by means of dimensional analytical method. The physical phenomenon of the local scour of the pipeline was modeled in a unidirectional flow flume. The experimental observation indicates that the process of the local scour around the pipeline with an initial embedment mainly includes four characteristic stages: (1) suspension of pipeline, (2) tunnel erosion, (3) lee-wake erosion and (4) equilibrium scouring stages. In the subcritical flow regime, there exists low correlativity between the equilibrium scour depth and Reynolds number. In the case of clear-water scour, the equilibrium scour depth increases with increasing Shields number, and descends linearly with increasing initial gap-diameter ratio in the examined range of initial gap-diameter ratios ( ).