The influence of pull-out load on the efficiency of jetting during spudcan extraction |
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| Authors: | Britta Bienen Christophe Gaudin Mark J Cassidy |
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| Institution: | 1. Centre for Offshore Foundation Systems (COFS), The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia;2. School of Engineering, The University of Melbourne, Melbourne School of Engineering Building 168, VIC 3010, Australia;3. School of Civil, Environmental and Mining Engineering, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia;4. Senior Research Engineer (MS), Daewoo Shipbuilding & Marine Engineering Co. Ltd. (DSME), 5F, 26. Eulji-ro 5-gil, Jung-gu, Seoul, 100-210, Republic of Korea;1. College of Civil Engineering, Hunan University, Changsha, 410082, PR China;2. School of Civil, Environmental and Mining Engineering, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia;3. Centre for Offshore Foundation Systems (COFS), The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia;4. State Key laboratory of Subtropical Building Science, South China Institute of Geotechnical Engineering, South China University of Technology, 381 Wushan Road, Guangzhou, 510640, China;1. State Key Laboratory of Hydraulic Engineering Simulation and Safety, Tianjin University, 92 Weijin Road, Nankai District, Tianjin 300072, China;2. CCCC Tianjin Port Engineering Institute Co., Ltd., 1002 Dagunan Road, Hexi District, Tianjin 300222, China |
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| Abstract: | Mobile jack-up drilling rigs are deployed at many locations during their service life. This necessitates retrieval of the platform’s legs and spudcan footings before the rig move. In soft soils, where the spudcans embed deeply, the extraction process can be difficult, time consuming and therefore costly. Water jetting systems, devised to ease spudcan extraction, are a common feature on modern jack-up units. However, their effectiveness in reducing the pull-out load required is questioned by the offshore industry. To investigate their efficiency, centrifuge experiments of a reduced scale spudcan model with jets have been performed at the University of Western Australia. The footing was extracted from penetrations of up to 1.5 diameters in normally consolidated clay. Similar to spudcan extraction in the field, these were carried out under load control, applying a constant extraction force. Both influences of pull-out load magnitude and jetting flow rate were investigated. The study demonstrates that jetting is efficient in facilitating spudcan extraction, as it reduces the required uplift load. Practical guidance is provided in applying the results to field conditions. |
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