Scour under submarine pipelines in waves in shoaling conditions

Submarine pipelines, one of the most important subjects in coastal engineering, are widely used in coastal structures. In order to ensure these pipelines are stable and functional during their project life, attention must be paid to their design and coastal processes. In the design phase, the possibility of local scouring under submarine pipelines must be taken into consideration. If local scour occurs under the submarine pipelines, the pipelines may either vibrate due to the hydrodynamic forces or induce additional static or dynamic loads due to self-burial. Moreover, they might be destroyed partially or fully and thus be unable to perform their functions. This paper presents experimental investigations of scour depth with respect to water depth using regular waves. The investigations encompass shoaling region conditions. Results of the measurements of velocities and beach profiles are enlightening, both for understanding of the mutual interaction between the disturbed flow field around the pipe and the seabed morphology as well as in making predictions of scour depth around submarine pipelines. Based on the present experimental data, a new equation is proposed, relating the maximum equilibrium scour depth to the modified Ursell number for the live bed condition for a rigid pipe fixed initially in contact with the bed.