Development of a design methodology for pipelines in ice scoured seabeds

Large areas of the continental shelf of northern oceans are frequently scoured or gouged by moving bodies of ice such as icebergs and sea ice keels associated with pressure ridges. This phenomenon presents a formidable challenge when the route of a submarine pipeline is intersected by the scouring ice. It is generally acknowledged that if a pipeline, laid on the seabed, were hit by an iceberg or a pressure ridge keel, the forces imposed on the pipeline would be much greater than it could practically withstand. The pipeline must therefore be buried to avoid direct contact with ice, but it is very important to determine with some assurance the minimum depth required for safety for both economical and environmental reasons. The safe burial depth of a pipeline, however, cannot be determined directly from the relatively straight forward measurement of maximum scour depth. The major design consideration is the determination of the potential sub-scour deformation of the ice scoured soil. Forces transmitted through the soil and soil displacement around the pipeline could load the pipeline to failure if not taken into account in the design. If the designer can predict the forces transmitted through the soil, the pipeline can be designedmore » to withstand these external forces using conventional design practice. In this paper, the authors outline a design methodology that is based on phenomenological studies of ice scoured terrain, both modern and relict, laboratory tests, centrifuge modeling, and numerical analysis. The implications of these studies, which could assist in the safe and economical design of pipelines in ice scoured terrain, will also be discussed.« less