Subsea pipelines passing through the shallow waters are usually buried inside the subsea trenches that are backfilled with pre-excavated material as a cost-effective protection solution. Buried pipelines may undergo large lateral displacements due to ground movement, landslides, ice scour, etc. Environmental, constructional, and operational loads significantly remould the backfilling material and make it much softer than the trench wall or native ground. This aspect that significantly affects the lateral pipe-soil interaction is not considered by current design standards due to the less explored interactive soil failure mechanisms around the trenched-backfilled pipeline. In this study, the lateral pipeline-backfill-trench interaction and the resultant soil failure mechanisms were investigated by centrifuge tests. Transparent observation windows equipped with digital cameras and state-of-the-art instrumentation were used to monitor the soil deformations directly and run particle image velocimetry (PIV) analysis. Using the experimental observations the influence of range of constructional and operational considerations on lateral response of the pipeline were discussed such as trenching and backfilling methodology, construction procedure, construction season, operational loads, environmental and operational thermal effects, longitudinal seabed profile, pipe weight, pipe type, backfill properties, backfill buoyancy, etc. Several new research avenues were identified, and their significance in assessing the ultimate pipeline response to lateral loads was discussed. The study showed that the trenching and backfilling could decrease the ultimate lateral soil resistance for large pipeline displacements, and increase for small and moderate pipeline relocations. The magnitude of such oscillation is significantly dependent on constructional and operational effects.
Hodjat Shiri and Morteza Kianian
Keywords: Lateral pipe-soil interaction, p-y response, large deformation, centrifuge testing, trenching and backfilling
Publisher: DFI