Advanced pipe-soil interaction models in finite element pipeline analysis

Offshore pipelines laid on the seabed are exposed to hydrodynamic and cyclic operational loading. As a result, they may experience on-bottom instabilities, walking and lateral buckling. Finite element simulations are required at different stages of the pipeline design to check the different loading cases. Pipeline design is dependent on accurate modelling of axial and lateral soil resistances (Bruton, 2008). The pipe-soil interaction of surface laid pipelines is still too often modelled using single frictional factors in the axial and lateral directions. These assumptions are too simplistic, especially in soft deepwater clay. Improved modelling of the pipe-soil interaction can help significantly reduce costs through optimising pipeline design.

Based on recent research, these simple models were improved and implemented in a finite element software program for pipeline analysis, to better simulate the pipe-soil interaction of surface laid pipelines and to more accurately simulate full routes. In this paper, the main features of the soil models are explained. There are several improvements. A more recent pipe-soil vertical reaction law that models plastic unloading is built into the program. It considers lay and dynamic installation effects to compute a more representative pipeline embedment. Axial and lateral resistance is now linked to pipeline embedment. Finally, peak-residual axial and lateral reaction laws are implemented.

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