Combined wave-current induced seabed liquefaction around buried pipelines: Design of a trench layer

With the increasing development and utilization of offshore oil and gas resources, seabed instability around pipelines subjected to combined ocean wave and current loadings and protection of the pipelines are becoming increasingly important. As a general practice, it is recommended to use trenching in shallow water region for the protection of submarine pipelines from the danger caused by storm waves and ocean currents changing level of the seabed. For a better understanding of the physical process involved in wave-current-seabed-pipeline interactions (WCSPI), a workable Finite Volume Model (FVM) is proposed to simulate wave-current induced soil responses around offshore pipelines. Based on the established FVM model, this study investigates the momentary soil liquefaction induced by various environmental loadings in ocean environments. In the present model, data exchange is taken place on the seabed surface to couple the flow and seabed sub-models. Unlike most previous studies, ocean currents are included in the present model, in which the Volume-Averaged Reynolds-Averaged Navier-Stokes (VARANS) equation is employed to govern non-linear fluid motions, while Biot's consolidation equation is used to link solid-pore fluid interactions in porous mediums. Numerical examples demonstrate the significant influence of ocean currents, trench geometry, and self-weight of the pipe on the wave-induced pore pressures and on the resultant seabed liquefaction around the pipeline.