FURTHER DEVELOPMENT AND BENCHMARKING OF A NOVEL PIPE-SOIL INTERACTION MODEL FOR SUBSEA PIPELINE DESIGN

For well over a decade it has been widely recognised that our existing models and tools for subsea pipeline stability design fail to account for the fact that seabed soils tend to become mobile well before the onset of pipeline instability. Despite ample evidence obtained from both laboratory and field observations that sediment mobility has a key role to play in understanding pipeline/soil interaction, no models have been presented previously which account for the tripartite interaction between the fluid and the pipe, the fluid and the soil, and the pipe and the soil. This paper presents further development of a novel non-cohesive pipe-soil interaction algorithm which has been developed to enable modelling of pipe-soil-fluid interaction and offer a more realistic representation of the evolution of soil profiles around the pipeline compared to existing hysteresis friction spring approaches. The paper describes the methods applied to discretisation of the soil profile and interpolation between timesteps to conserve soil volume. The approach used to deform the seabed profile to account for pipe movement and predict pipeline / soil reaction forces enable the model to be benchmarked against the Verley model [12]. The model has been specifically developed to minimise computational cost compared to computationally intensive CEL continuum soil FEA approaches [6,14], but still enable the profile of the soil around the pipe to be established. This model has application to modelling of sediment transport and scour [4]. It may also offer advantages in the modelling of globally buckling pipelines where differing levels of embedment and support at buckle shoulders versus the apex of the buckle are not well handled by existing approaches. The model may also assist where existing, generally applied approaches are also not well developed to capture coupling of behaviour in axial and lateral resistances.