In a recent Gulf of Mexico deepwater development project, two hybrid subsea foundations (HSF) were designed, fabricated and successfully installed for two flowline end terminations (FLETs) in approximately 2,170 meter water depth. The HSF is an attractive option when a subsea structure is subjected to substantial lateral loads, vertical loads and overturning moments that cannot be effectively resisted by a typical shallow (mudmat) foundation. A new HSF design methodology was established and a pile head locking system was developed by the project team. This is the first offshore application of the HSF concept utilizing the vertical resistance from the corner piles in addition to their lateral resistance via a custom designed pile head locking system. In configuring the pile head locking system to provide pile head fixity, the gap between the sleeve and the pile became one of the governing factors for design, fabrication and installation of the HSF. This paper presents the case history of the successful project execution covering the detailed design, fabrication and staged installation. Foundation selection during the detailed design stage, description of the pile locking system, preventive measures taken during the fabrication stage, back analysis results from the installation stages and pictures taken by remotely operated vehicles (ROVs) during the FLET HSF installation are presented.
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