Partially Mobile Shallow Subsea Foundations: A Practical Analysis Framework
Publication: Journal of Geotechnical and Geoenvironmental Engineering
Volume 147, Issue 8
Abstract
The geotechnical design of partially mobile subsea foundations (mudmats) for pipeline/flowline end terminals (PLETs) is presented in this paper. A partially mobile mudmat represents a fit-for-purpose engineering solution that has significant commercial competitiveness. The partially mobile design lies between that of a fully anchored mudmat (which is designed for negligible movements but may be too large, causing installation issues or requiring corner piles to anchor) and a fully mobile mudmat (which moves to fully accommodate the expansion of the connected pipeline, but may suffer excessive settlements that compromise the structural integrity). The partially mobile mudmat is suited to deepwater soft soil conditions. The aim of this work is to help mature this new concept and technology for practical design and to inspire future research to improve the accuracy of predictions. The objective of the paper is to present simple new analytical solutions to predict the long-term accumulated displacements and rotations of a partially mobile mudmat on soft clayey deposits subjected to cyclic loading. The proposed displacement prediction framework combines established elements of consolidation theory, plasticity theory, and critical-state soil mechanics (CSSM). Typical ranges of soil properties pertinent to a partially mobile mudmat are provided for deepwater Gulf of Mexico (GoM) soft clays, and a design analysis example is provided. For these conditions, it is concluded that the dominant displacements of a partially mobile mudmat are caused by primary consolidation and plastic failure. Recommendations for further improvement are provided to inspire further research.
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Data Availability Statement
The following data, models, or code generated or used during the study are available from the corresponding author by request: derivation of the associated flow rule from the mudmat failure envelope.
Acknowledgments
The authors thank the management of Shell Global Solutions (US) Inc. and Shell International Exploration and Production Inc. for permission to publish this paper. D. White acknowledges the support of the Shell Chair in Offshore Engineering, funded by Shell Australia, which supported early work on this paper while he was based at the University of Western Australia. The views and opinions are those of the authors alone and do not necessarily reflect those of any of the sponsors or other contributors.
References
API RP2GEO (American Petroleum Institute). 2014. API recommended practice, geotechnical and foundation design considerations. Farmington Hills, MI: ACI.
Cocjin, M. L., S. M. Gourvenec, D. J. White, and M. F. Randolph. 2014. “Tolerably mobile subsea foundations—Observations of performance.” Géotechnique 64 (11): 895–909. https://doi.org/10.1680/geot.14.P.098.
Cocjin, M. L., S. M. Gourvenec, D. J. White, and M. F. Randolph. 2017. “Theoretical framework for predicting the response of tolerably mobile subsea installations.” Géotechnique 67 (7): 608–620. https://doi.org/10.1680/jgeot.16.P.137.
Corti, R., S. M. Gourvenec, M. F. Randolph, and A. Diambra. 2017. “Application of a memory surface model to predict whole-life settlements of a sliding foundation.” Comput. Geotech. 88 (Aug): 152–163. https://doi.org/10.1016/j.compgeo.2017.03.014.
Das, B. M. 2013. Advanced soil mechanics. London: CRC Press.
Deeks, A., H. Zhou, H. Krisdani, F. Bransby, and P. Watson. 2014. “Design of direct on-seabed sliding foundations.” In Vol. 45411 of Proc., Int. Conf. on Offshore Mechanics and Arctic Engineering, V003T10A024. New York: ASME.
Dimmock, P., E. Clukey, M. F. Randolph, D. Murff, and C. Gaudin. 2013. “Hybrid subsea foundations for subsea equipment.” J. Geotech. Geoenviron. Eng. 139 (12): 2182–2192. https://doi.org/10.1061/(ASCE)GT.1943-5606.0000944.
Feng, X., and S. Gourvenec. 2015. “Consolidated undrained load-carrying capacity of subsea mudmats under combined loading in six degrees of freedom.” Géotechnique 65 (7): 563–575. https://doi.org/10.1680/geot.14.P.090.
Feng, X., and S. Gourvenec. 2016. “Modelling sliding resistance of tolerably mobile subsea mudmats.” Géotechnique 66 (6): 490–499. https://doi.org/10.1680/jgeot.15.P.178.
Feng, X., M. Randolph, S. Gourvenec, and R. Wallerand. 2014. “Design approach for rectangular mudmats under fully three-dimensional loading.” Géotechnique 64 (1): 51–63. https://doi.org/10.1680/geot.13.P.051.
Geoconsulting, F. 2015. Project report on pipe-soil interaction tests to Shell. Oak Park, MI: Global Solutions US Inc.
Holl, D. L. 1940. “Stress transmissions in earths.” In Vol. 20 of Proc., 20th Annual Meeting of the Highway Research Board, edited by R. W. Crum, 709–721. Washington, DC: Transportation Research Board.
ISO. 2016. Petroleum and natural gas industries: Specific requirements for offshore structures, Part 4: Geotechnical and foundation design considerations. ISO 19901-4. Geneva: ISO.
Krost, K., S. Gourvenec, and D. White. 2011. “Consolidation around partially embedded seabed pipelines.” Géotechnique 61 (2): 167–173. https://doi.org/10.1680/geot.8.T.015.
Laham, N., K. Kwa, D. White, and S. Gourvenec. 2021. “Episodic direct simple shear tests to measure changing strength for whole-life geotechnical design.” Géotech. Lett. 11 (1): 103–111.
NAVFAC (Naval Facilities Engineering Command Publications Transmittal). 1986. Soil mechanics design manual 7.01. Alexandria, VA: NAVFAC.
Ohara, S., and H. Matsuda. 1988. “Study on the settlement of saturated clay layer induced by cyclic shear.” Soils Found. 28 (3): 103–113. https://doi.org/10.3208/sandf1972.28.3_103.
Randolph, M., D. White, and Y. Yan. 2012. “Modelling the axial soil resistance on deep-water pipelines.” Géotechnique 62 (9): 837–846. https://doi.org/10.1680/geot.12.OG.010.
Roscoe, K. H., and J. Burland. 1968. “On the generalized stress-strain behaviour of wet clay.” In Engineering plasticity, edited by J. Heyman and F. A. Leckie, 535–609. Cambridge, UK: Cambridge University Press.
Schofield, A., and P. Wroth. 1968. Critical state soil mechanics. London: McGraw-Hill.
Vulpe, C., S. M. Gourvenec, and A. F. Cornelius. 2016. “Effect of embedment on consolidated undrained capacity of skirted circular foundations in soft clay under planar loading.” Can. Geotech. J. 54 (2): 158–172. https://doi.org/10.1139/cgj-2016-0265.
Wallerand, R., B. Stuyts, M. Blanc, L. Thorel, and N. Brown. 2015. “A design framework for sliding foundations: Centrifuge testing and numerical modelling.” In Proc., Offshore Technology Conf. Richardson, TX: Society of Petroleum Engineers.
White, D., J. Chen, S. Gourvenec, and C. O’Loughlin. 2019. “On the selection of an appropriate consolidation coefficient for offshore geotechnical design.” In Proc., Int. Conf. on Offshore Mechanics and Arctic Engineering, V001T010A021. New York: ASME.
Yasuhara, K., and K. H. Andersen. 1991. “Recompression of normally consolidated clay after cyclic loading.” Soils Found. 31 (1): 83–94. https://doi.org/10.3208/sandf1972.31.83.
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Published In
Journal of Geotechnical and Geoenvironmental Engineering
Volume 147 • Issue 8 • August 2021
Copyright
© 2021 American Society of Civil Engineers.
History
Received: Nov 9, 2020
Accepted: Apr 2, 2021
Published online: May 28, 2021
Published in print: Aug 1, 2021
Discussion open until: Oct 28, 2021
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