Pipe-Soil Interaction for Surface-Laid Pipelines in Carbonate Sediments-Paper

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The paper examines pipe–soil interaction (PSI) for surface-laid pipelines on carbonate seabeds, where existing design guidance is largely based on tests in clay or siliceous sand and may not represent actual conditions.<br /><br />Carbonate sediments can be highly variable and contain angular, crushable grains with broad particle-size distributions. Their properties can produce high friction and pipe–soil interface resistance, substantial cyclic strength loss and remoulding, and drainage behaviour that shifts between undrained and drained depending on loading rate. These characteristics affect pipeline embedment and lateral and axial resistance.<br /><br />Comparisons of tests with code-based calculations show important discrepancies. Existing methods may significantly underestimate as-laid embedment, particularly in drained carbonate sands. Since embedment strongly influences predicted resistance, these errors can affect pipeline stability and operational response. Generic methods can also misestimate lateral residual resistance: contractile carbonate silts may provide less resistance than predicted, while dilatant carbonate silty sands may provide more. Drained resistance depends strongly on the roughness of the pipeline–soil interface, which standard assumptions may not capture. Axial resistance calculations must account for site-specific interface strength, drainage, and changes in soil stress history during installation and operation.<br /><br />The authors recommend detailed, site-specific seabed characterization and zoning along pipeline routes, together with testing that represents the actual soil and pipeline surface. Calculations should explicitly consider carbonate soil properties, installation effects, drainage transitions, and statistical uncertainty. Where possible, project-specific model tests, interface tests, numerical analyses, and back-analysis of nearby pipelines should validate predictions. Overall, unmodified code-based methods derived from non-carbonate soils may produce unreliable design inputs for carbonate seabeds.

Keywords

pipe-soil interaction

carbonate seabeds

surface-laid pipelines

pipeline embedment

lateral resistance

axial resistance

carbonate sediments

drained behavior

interface roughness

site-specific design