Lateral resistance of "rigid" pipelines and cables on rocky seabeds

Abstract

Accurate assessment of lateral resistance is critical to ensure the on-bottom stability and integrity of subsea pipelines and cables in the oil/gas and marine renewable energy industries. However, on rocky seabeds recommend practices provide limited recommendations on pipe/seabed interaction, suggesting only a single value for the friction coefficient of 0.6. This paper reports on a programme of physical experiments and theoretical modelling investigating the lateral resistance of pipes on rocky seabeds. It is shown that the peak and mean effective friction can significantly exceed the interface (or Coulomb) friction coefficient when the pipe diameter (D) is similar to the median rock diameter (dn50). Only when the pipe diameter becomes large compared to the rock size does the mean effective friction approach the interface friction. The effective friction coefficient was found to vary with variability in rock size and shape, as well as the length of pipe relative to median rock diameter. Each of these findings is reproduced well using the theoretical model and demonstrating that the effective lateral friction coefficient maybe higher than 0.6 for mean friction, and significantly higher for peak friction. This implies that inaccuracy may exist in current design, which may be rectified using the theoretical model.

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ORCID for David White: orcid.org/0000-0002-2968-582X

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