Constructional and Operational Considerations in Assessing the Lateral Response of Buried Subsea Pipelines-Paper

Paper

Pdf Summary

The study examines how trenching, backfilling, and project-specific construction and operational conditions affect the lateral resistance of buried subsea pipelines. Current design standards often model the soil as uniform, overlooking the softer, disturbed backfill and its interaction with the native trench walls. This simplification may lead to either overestimation or underestimation of pipeline resistance.<br /><br />The authors conducted centrifuge tests using clay native soil and three backfill types: very soft slurry, remoulded chunky clay, and loose sand. Cameras and particle image velocimetry were used to observe soil deformation and failure mechanisms as model pipelines were displaced laterally. The tests also examined how the intensity of pipe–trenchbed interaction influences the response.<br /><br />Results show that backfill stiffness and pipe–trenchbed interaction can substantially change lateral resistance. Stronger backfill provides passive pressure that helps prevent trench-wall collapse and can increase ultimate resistance. Very soft backfill offers little support, allowing larger-scale failure and reducing resistance at large displacements. More intense interaction with the trench bed can accelerate failure in the trench wall and reduce ultimate resistance. The effects vary with displacement: trenching and backfilling may increase resistance at small or moderate movements but decrease it at large movements.<br /><br />Factors that may affect backfill stiffness or bed interaction include trenching and backfilling methods, construction procedure and season, operational loads and thermal effects, seabed profile, pipe weight and type, backfill properties, and buoyancy. The authors conclude that these conditions should be incorporated into project-specific assessments and that further research is needed to improve the accuracy and reliability of pipeline design.

Keywords

subsea pipelines

lateral resistance

trenching

backfilling

backfill stiffness

clay soil

centrifuge tests

trench-wall failure

pipe-soil interaction

pipeline design