Analysis of Soil Strength Degradation during Episodes of Cyclic Loading, Illustrated by the T-Bar Penetration Test
Publication: International Journal of Geomechanics
Volume 10, Issue 3
Abstract
Pipelines and risers form an essential part of the infrastructure associated with offshore oil and gas facilities. During installation and operation, these structures are subjected to repetitive motions which can cause the surrounding seabed soil to be remolded and soften. This disturbance leads to significant changes in the operative shear strength, which must be assessed in design. This paper presents an analytical framework that aims to quantify the degradation in undrained shear strength as a result of gross disturbance—in this case through repeated vertical movement of a cylindrical object embedded in undrained soil. The parameters of the framework were calibrated using data obtained in a geotechnical centrifuge test. In this test a T-bar penetrometer, which is a cylindrical tool used to characterize the strength of soft soil, was cycled vertically in soil with strength characteristics typical of a deep water seabed. Using simple assumptions regarding the spatial distribution of “damage” resulting from movement of the cylinder, and by linking this damage to the changing undrained shear strength via a simple degradation model, the framework is shown to simulate well the behavior observed in a cyclic T-bar test. This framework can potentially be extended to the similar near-surface behavior associated with seabed pipelines and risers.
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Acknowledgments
The work described here forms part of the activities of the Centre for Offshore Foundation Systems (COFS), established under the Australian Research Council’s Research Centres Program and now supported by Centre of Excellence funding from the State Government of Western Australia. The first writer acknowledges the financial support he receives from the Western Australia Energy Research Alliance (WA:ERA). The assistance provided by senior centrifuge technician Don Herley is acknowledged.
References
Aubeny, C. P., Shi, H., and Murff, J. D. (2005). “Collapse loads for a cylinder embedded in trench in cohesive soil.” Int. J. Geomech., 5(4), 320–325.
Bridge, C. D., and Howells, H. A. (2007). “Observations and modeling of steel catenary riser trenches.” Proc., Int. Offshore and Polar Engineering Conf., International Society of Polar and Offshore Engineering, Lisbon, Portugal, 803–813.
Bridge, C. D., Laver, K., Clukey, E. C., and Evans, T. R. (2004). “Steel catenary riser touchdown point vertical interaction model.” Proc., Offshore Technology Conf., Houston, OTC 16628.
Bruton, D. A. S., White, D. J., Carr, M. C., and Cheuk, C. Y. (2008). “Pipe-soil interaction during lateral buckling and pipeline walking: The Safebuck Jip.” Proc., Offshore Technology Conf., Houston, OTC 19589.
Clukey, E. C., Haustermans, L., and Dyvik, R. (2005). “Model tests to simulate riser-soil interaction in touchdown point region.” Proc., Int. Symp. on Frontiers in Offshore Geotechnics, Taylor & Francis, Perth, Australia, 651–658.
Dingle, H. R. C., White, D. J., and Gaudin, C. (2008). “Mechanisms of pipe embedment and lateral breakout on soft clay.” Can. Geotech. J., 45(5), 636–652.
Einav, I., and Randolph, M. F. (2005). “Combining upper bound and strain path methods for evaluating penetrometer resistance.” Int. J. Numer. Methods Eng., 63, 1991–2016.
Hodder, M. S., White, D. J., and Cassidy, M. J. (2008). “Centrifuge modelling of riser-soil stiffness degradation in the touchdown zone of a steel catenary riser.” Proc., Int. Conf. on Offshore Mechanics and Arctic Engineering, American Society of Mechanical Engineering, Estoril, Portugal.
Klar, A., and Osman, A. S. (2008). “Continuous velocity fields for the T-bar problem.” Int. J. Numer. Analyt. Meth. Geomech., 32(8), 949–963.
Lehane, B. M., O’Loughlin, C. D., Gaudin, C., and Randolph, M. F. (2009). “Rate effects on penetrometer resistance in kaolin.” Geotechnique, 59(1), 41–52.
Martin, C. M., and Randolph, M. F. (2006). “Upper bound analysis of lateral pile capacity in cohesive soil.” Geotechnique, 56(2), 141–145.
Palmer, A. (2000). “Catenary riser interaction with the seabed at the touchdown point.” Proc., Deepwater Pipeline and Riser Technology Conf., Pennwell, Houston.
Randolph, M. F., Low, H. E., and Zhou, H. (2007). “In situ testing for design of pipeline and anchoring systems.” Proc., 6th Int. Conf on Offshore Site Investigation and Geotechnics, Society for Underwater Technology, London.
Randolph, M. F., and White, D. J. (2008). “Upper bound yield envelopes for pipelines at shallow embedment in clay.” Geotechnique, 58(4), 297–301.
Wroth, C. P. (1984). “Interpretation of in situ soil tests.” Geotechnique, 34(4), 449–489.
Zhou, H., and Randolph, M. F. (2009). “Resistance of full-flow penetrometers in rate-dependent and strain-softening clay.” Geotechnique, 59(2), 79–86.
Information & Authors
Information
Published In
International Journal of Geomechanics
Volume 10 • Issue 3 • June 2010
Pages: 117 - 123
Copyright
© 2010 ASCE.
History
Received: Dec 9, 2008
Accepted: Sep 9, 2009
Published online: Sep 30, 2009
Published in print: Jun 2010
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