90 / 2025-04-24 12:55:56

The Nature of Sediment that Accumulates around Subsea Pipelines and Cables

Subsea pipelines and cables may experience changes in burial conditions during their lifetime. Estimating the level of burial is an important input to assessing operational response, e.g. for predicting the seabed resistance of controlled/uncontrolled buckling. However, there is a lack of understanding of the properties of sediment that accumulates around the pipeline: is it looser, denser or the same as the undisturbed soil at the location; is it finer or coarser than surrounding sediment? Current practice is to assume the burial sediment is the same as the intact seabed, but the appropriateness of this is untested and leads to uncertainty. This study investigates the burial process and the resulting state of the sediment around the pipeline. This was achieved by performing O-tube (i.e. sealed flume) model tests in both silica sand and carbonate silty sand, with subsequent measurement of changes of soil density and grain size at locations around the pipe. The ability of the experiments to represent realistic burial processes is validated by comparing the achieved profile in model tests with the field observations. The results improve our understanding of fundamental processes occurring during the life of a pipeline or cable, and are a consideration for future design practice.