Sediment Mobility Effects on Seabed Resistance for Unburied Pipelines

In order to design unburied pipelines, pipeline engineers require information about lateral and axial seabed resistances (normally known as 'friction factors') prior to and during operation. Geotechnical engineers must provide this information based on knowledge of pipeline properties, seabed conditions and metocean conditions. Accurate prediction of the seabed resistances requires accurate prediction of pipeline embedments. This paper discusses how pipeline embedments and geometries can change from the as-laid state as the result of sediment mobility around pipelines and demonstrates how these embedment changes will change the pipe-soil friction factors using a series of numerical analyses. Sediment mobility tends to cause a general trend of increasing pipe embedment, which is beneficial for hydrodynamic stability but can be onerous for thermal buckling. Recommendations are provided to accommodate these effects in design, without unnecessary levels of over-conservatism.