Subsea pipeline walking: The effect of a bi-linear seabed friction model

Abstract

The objective of this paper is to explore the gaps in the present analysis methods proposed by various joint industry projects and others for pipeline walking behaviour. Thereafter, present analytical methods are extended to bridge the gap between analytical modelling tools and numerical analysis, by extending analytical models to encompass bi-linear soil friction behaviour. In the analytical solution, the pipe-soil interaction is usually modelled as rigid-plastic, expressed as ultimate resistance per unit length. Often this term is expressed non-dimensionally as a friction factor, µ. However, the elastic-plastic (i.e. bi-linear) behaviour of the soil and the effect of this bi-linear response of the soil on the walking behaviour were not addressed in the literature. The elastic-plastic behaviour is often represented by an additional parameter, specified as the mobilisation displacement. This is defined as the amount of axial displacement that occurs before the ultimate friction is generated, and the resistance rises linearly with displacement up to this value. The walking behaviour is affected by the axial friction mobilisation displacement. The existing analytical solutions are extended to incorporate the elastic-plastic response of the soil into the expression of pipeline walking, supported by a new derivation. Numerical verification with ABAQUS is also provided for the proposed expression.

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ORCID for David White: orcid.org/0000-0002-2968-582X

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