Abstract
This paper examines possible causes of additional spudcan settlement after preloading using both centrifuge model tests and small strain finite element analysis, in which spudcan settlement due to cavity collapse, consolidation settlement and settlement due to cyclic loading are incorporated. Back-analyses of seven jack-up rigs in the Gulf of Mexico show that even complete cavity collapse could only explain part of the measured additional settlements in the majority of the cases. Small strain finite element analyses also show that spudcan consolidation settlement is likely to account for even less of the additional settlement than cavity collapse in the sites considered. On the other hand, centrifuge model tests show that large amplitude cyclic rocking has a very significant effect on spudcan settlement, even if half of the preload has been removed. However, this effect cannot be explained by the exceedance of the yield envelope since the loading combination had not exceeded the yield envelope. One possible explanation is the stiffness and strength degradation of the soil under cyclic loading. In view of this, a conservative approach is recommended in instances where large amplitude cyclic rocking, such as that arising from storm loading, is expected shortly after preloading. The presence of lattice legs is found to reduce the spudcan settlement during large amplitude cyclic rocking.
Highlights
Bearing capacity of spudcan foundations for offshore mobile jack-up rigs is currently assessed using methods recommended by ISO [1]
The forgoing discussion explored the possible causes on additional spudcan settlements after the completion of preloading in the Gulf of Mexico sites, the findings show that full cavity collapse could only explain part of the measured additional settlements
Consolidation settlement is likely to account for a small proportion of the spudcan settlement, probably less significant than that caused by cavity collapse
Summary
Bearing capacity of spudcan foundations for offshore mobile jack-up rigs is currently assessed using methods recommended by ISO [1]. Which did not appear to be caused by punch-through They attributed this to an unaccounted-for loading possibly arising from soil “backflow” into the cavity. ISO [1] indicates that spudcan settlement may consist of four components, i.e. elastic settlement, consolidation settlement, settlement due to cyclic loading, and settlement due to seabed instability. The elastic settlement is the component which occurs immediately on loading application. This component is often not critical post-installation since it would have taken place upon application of preload. This paper examines three components of the spudcan settlement, i.e elastic settlement due to cavity collapse, consolidation settlement and settlement due to cyclic loading, using both centrifuge model tests and finite element analyses. Effects of lattice legs on these spudcan settlement components are incorporated
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
