Ocean-current-induced pipeline stability on sandy seabed was simulated physically in a flow flume. The process of pipeline losing onbottom stability in currents was recorded and analyzed. Experimental data show that, for a pipeline directly laid on sandy seabed, there exists a linear relationship between the dimensionless submerged weight of pipeline and Froude number, in which the current-pipe-soil coupling effects are reflected. The sand-particle size effects on pipeline onbottom stability are further discussed. The new established empirical relationship may provide a guide for the engineering practice of current-induced on-bottom stability design of a submarine pipeline.
When a submarine pipeline is installed upon sandy seabed, there exists a complex interaction between pipeline, seabed and ocean environmental loads. To keep the pipeline stable on the seabed, the soil must provide enough resistance to balance the hydrodynamic forces. Otherwise, the pipeline will breakout from its original site, i.e. pipeline on-bottom instability occurs. In the practice of submarine pipeline stability design, the submerged weight of pipeline is a key factor for influencing the soil resistance. To get a heavier pipeline, thickness of cover layer has usually to be increased. Nevertheless, a slight increase of submerged weight will bring a larger laying cost, and sometimes will make the existing laying barges unworkable. Therefore, an appropriate criterion for pipeline stability is highly desired for the determination of pipeline's submerged weight. In the past few decades, the dynamics interactions between wave/current-pipeline-seabed have attracted much interest from pipeline researchers and designers. In the 1980" s, the pipeline on-bottom stability has been investigated mainly by physical modeling in a few large projects, such as the PIPESTAB project (Wagner et al., 1987), the AGA project (Brennodden et al., 1989) and a project at DHI (Palmer et al., 1988).