Penetration Resistance of Offshore Skirted Foundations and Anchors in Dense Sand
Publication: Journal of Geotechnical and Geoenvironmental Engineering
Volume 134, Issue 1
Abstract
Penetration of skirts is an essential design issue for offshore skirted foundations and anchors in sand. Skirts may not penetrate far enough into dense sand by the available submerged weight alone. It may therefore be necessary to apply underpressure inside the skirt compartment to produce an increased driving force and to reduce the penetration resistance. This paper recommends procedures to calculate penetration resistance and required underpressure for skirts penetrated in dense sand with and without interbedded clay layers. The recommendations are based on interpretation of skirt penetration data from prototypes, field model tests, and laboratory model tests in dense sand. The paper first presents a model to calculate the penetration resistance of skirts penetrated by weight, or other external vertical load that does not cause flow of water in the sand. Two models are considered; one based on bearing capacity equations with friction angles from laboratory tests, and the other one based on empirical correlations with CPT tip resistance. The bearing capacity model gives more consistent correlations with the empirical data than the CPT model. Thereafter, a model to account for the effect of underpressure applied inside the skirt compartment is proposed. This model is developed based on interpretation of available prototype and model test data from skirts penetrated by underpressure. The results show that underpressure facilitates skirt penetration in sand considerably by providing both an additional penetration force and a reduced penetration resistance. It is also shown that interbedded clay layers can prevent flow of water through the sand and eliminate the beneficial reduction in penetration resistance.
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Acknowledgments
The writers would like to thank Statoil, Chevron Petroleum Technology Company, Conoco Inc., Petrobras, and Saudi Aramco, which sponsored the joint industry project within which the work described herein was performed. Statoil and BP are also acknowledged for their release of skirt penetration data. Contributions from Tor Inge Tjelta of Statoil in his active involvement to initiate the project and as chairman of the steering committee, Per Sparrevik of NGI regarding information and discussions of the model tests at NGI, and Niels Mortensen of NGI regarding discussions of calculation procedures and ring shear tests to determine interface friction between skirt and sand are also greatly appreciated.
References
American Petroleum Institute (API). (1993). “Recommended practice for planning, designing and constructing fixed offshore platforms.” API RP 2A, American Petroleum Institute, Washington, D.C.
Andersen, K. H., Murff, J. D., Randolph, M. F., Clukey, E., Erbrich, C., Jostad, H. P., Hansen, B., Aubeny, C., Sharma, P., and Supachawarote, C. (2005). “Suction anchors for deepwater applications.” Proc., Int. Symp. on Frontiers in Offshore Geotechniques (ISFOG), Keynote Lecture, Perth, Western Australia, 3–30.
Clausen, C. J. F. (1998). “Fundamentering av plattformer; Observasjoner og refleksjoner.” 16th Laurits Bjerrum Memorial Lecture, Norwegian Geotechnical Institute, Oslo.
Dendani, H., and Colliat, J. L. (2002). “Girassol: Design analysis and installation of the suction anchors.” Proc., Offshore Technology Conf., Houston, Paper No. 14209.
Erbrich, C. T., and Tjelta, T. I. (1999). “Installation of bucket foundations and suction caissons in sand—Geotechnical performance.” Proc., Offshore Technology Conf., Houston, Paper No. 10990.
Houlsby, G., and Byrne, B. W. (2005). “Design procedures for installation of suction caissons in sand.” Geotech. Eng., Proc., Institute of Civil Engineering, London, 158(GE3), 135–144.
Houlsby, G., Ibsen, L. B., and Byrne, B. W. (2005). “Suction caissons for wind turbines.” Keynote lecture, Proc., Int. Symp. on Frontiers in Offshore Geotechniques, Perth, Western Australia, 75–94.
Johansson, P., Aas, P. M., and Hansen, S. B. (2003). “Field model tests for a novel suction anchor application.” Proc., 6th Int. Symp. on Field Measurements in Geomechanics, Oslo, Norway.
Jostad, H. P., and Andersen, K. H. (2006). “Potential benefits of using skirted foundations for jack-up platforms.” Proc., Offshore Technology Conf., Houston, Paper No. 18016.
Sparrevik, P. (1995). “Development of new platform foundation concept through instrumentation.” Proc., 4th Int. Symp. on Field Measurements in Geomechanics, Bergamo, Italy, Paper, 137–144.
Tjelta, T. I. (1995). “Geotechnical experience from the installation of the Europipe jacket with bucket foundations.” Proc., Offshore Technology Conf., Houston, Paper No. 7795.
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© 2008 ASCE.
History
Received: Sep 25, 2006
Accepted: Feb 27, 2007
Published online: Jan 1, 2008
Published in print: Jan 2008
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