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Modelling the embedment process during offshore pipe-laying on fine-grained soils

Modelling the embedment process during offshore pipe-laying on fine-grained soils
Modelling the embedment process during offshore pipe-laying on fine-grained soils

Subsea pipelines are becoming an increasingly significant element of offshore hydrocarbon developments as exploration moves into deep-water environments further from shore. During the lay process, pipelines are subject to small amplitude vertical and horizontal oscillations, driven by the sea state and lay vessel motions. Centrifuge model tests have been used to simulate these small-amplitude lay effects, with varying degrees of idealization relative to the real lay process. In the soft soils found in deep water, pipe embedment can exceed a diameter or more, thus significantly affecting the lateral pipe-soil interaction, axial resistance, and thermal insulation. In this paper, results from centrifuge model tests are used to calibrate a model for calculating the dynamic embedment of a subsea pipeline. The model uses elements of plasticity theory to capture the effects of combined vertical and horizontal loading, and incorporates the softening of the surrounding soil as it is remoulded due to the pipeline motions. Influences from the lay rate, lay geometry, and sea state are included in the calculation process. The model is compared with observed as-laid pipeline embedment data from field surveys at three different offshore sites. Using site-specific soil parameters obtained from in situ testing and idealized pipe loads and motions to represent the load and displacement patterns during offshore pipe-laying, respectively, the model is shown to capture well the final as-laid embedment measured in the field surveys.

Centrifuge modeling, Clays, Offshore engineering, Pipe-laying, Plasticity
0008-3674
15-27
Westgate, Z.J.
983a044b-1644-4a5c-895d-6b7c83501ab9
White, D.J.
a986033d-d26d-4419-a3f3-20dc54efce93
Randolph, M.F.
75caa33a-e630-4ae8-84cd-758797bf9633
Westgate, Z.J.
983a044b-1644-4a5c-895d-6b7c83501ab9
White, D.J.
a986033d-d26d-4419-a3f3-20dc54efce93
Randolph, M.F.
75caa33a-e630-4ae8-84cd-758797bf9633

Westgate, Z.J., White, D.J. and Randolph, M.F. (2013) Modelling the embedment process during offshore pipe-laying on fine-grained soils. Canadian Geotechnical Journal, 50 (1), 15-27. (doi:10.1139/cgj-2012-0185).

Record type: Article

Abstract

Subsea pipelines are becoming an increasingly significant element of offshore hydrocarbon developments as exploration moves into deep-water environments further from shore. During the lay process, pipelines are subject to small amplitude vertical and horizontal oscillations, driven by the sea state and lay vessel motions. Centrifuge model tests have been used to simulate these small-amplitude lay effects, with varying degrees of idealization relative to the real lay process. In the soft soils found in deep water, pipe embedment can exceed a diameter or more, thus significantly affecting the lateral pipe-soil interaction, axial resistance, and thermal insulation. In this paper, results from centrifuge model tests are used to calibrate a model for calculating the dynamic embedment of a subsea pipeline. The model uses elements of plasticity theory to capture the effects of combined vertical and horizontal loading, and incorporates the softening of the surrounding soil as it is remoulded due to the pipeline motions. Influences from the lay rate, lay geometry, and sea state are included in the calculation process. The model is compared with observed as-laid pipeline embedment data from field surveys at three different offshore sites. Using site-specific soil parameters obtained from in situ testing and idealized pipe loads and motions to represent the load and displacement patterns during offshore pipe-laying, respectively, the model is shown to capture well the final as-laid embedment measured in the field surveys.

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More information

Accepted/In Press date: 4 October 2012
e-pub ahead of print date: 22 October 2012
Published date: January 2013
Keywords: Centrifuge modeling, Clays, Offshore engineering, Pipe-laying, Plasticity

Identifiers

Local EPrints ID: 419921
URI: https://eprints.soton.ac.uk/id/eprint/419921
ISSN: 0008-3674
PURE UUID: bc851fef-f988-4eea-8383-6479bc550893
ORCID for D.J. White: ORCID iD orcid.org/0000-0002-2968-582X

Catalogue record

Date deposited: 23 Apr 2018 16:30
Last modified: 29 Aug 2019 00:25

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Contributors

Author: Z.J. Westgate
Author: D.J. White ORCID iD
Author: M.F. Randolph

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