Seabed friction on carbonate soils: Physical modelling of axial pipe-soil friction

This paper is concerned with the 'friction' and 'sliding resistance' that can be mobilised on the unusual carbonate sediments prevalent across many parts of the world, including Offshore Australia. Physical centrifuge model testing was conducted to evaluate the axial pipe-soil resistance on a soil obtained from the North West Shelf, offshore Australia. Tests were performed at a range of speeds, spanning drained/undrained conditions, interspersed with consolidation periods. The resulting axial friction factors are generally higher than is often assumed in conventional design practice for pipeline end expansion or buckling and walking analysis, which is consistent with the high friction angles and dilatancy of these angular carbonate soils. In addition, the results demonstrate the effect that soil drainage response and history of pipeline sliding movements can have on the axial-pipe friction. Overall, the results highlight the importance of making site-specific assessments of seabed sliding resistance, rather than rely on non-sitespecific results (particularly from different regions) that may display a very different soil response. Lastly, recommendations are made for design assessments of the sliding resistance of carbonate soils.