Correctly predicting pipe-seabed interaction (PSI) response is critical for surface-laid pipeline design. Recent updated codes and guidance documents are based on recent research that has mostly been conducted for (undrained) soft clays because the focus has been on HTHP pipelines, mostly in deep water. Consequently, the guidance on pipe-soil interaction behaviour in carbonate soils (as encountered for example, in the Arabian Gulf and the North-West Shelf of Australia) has not been updated, leaving the industry with open ended practices which may lead to questionable design. Pipe-soil interaction in carbonate soils will differ to 'conventional' soils (e.g. clays and clean silica sands) because of the higher sensitivities (increasing lay embedment), the higher angles of internal friction (leading to larger pipe-soil interface resistances and axial friction factors), the wider particle size distributions (which lead to soil drainage conditions depending on pipeline loading event) and the high degree of spatial variability. Each of these issues need to be addressed explicitly in any PSI calculation approach (and in the associated site investigation programme) in order to provide reliable pipeline design inputs. Consequently, this paper discusses carbonate soil PSI response and compares the results of PSI tests in carbonate soils to calculations using public domain code-based methods to give general recommendations about pipe-soil interaction on carbonate seabeds.
Fraser Bransby, Han Eng Low, Fangyuan Zhu, Romain Clavaud and David White
Keywords: Pipeline geotechnics, pipe-soil interaction, carbonate soils, site investigation
Publisher: DFI