Suction piles are widely used in deepwater engineering both for anchoring and as foundation systems. In the first case the piles serve as anchor points for mooring systems in alternative to more standard drag anchors or piles. More recently, however, they have been used as structure foundations. In this role suction piles are a competitive alternative to the more traditional solutions of driven piles or mudmats, for platform jackets, subsea systems and subsea equipment protection structures. This solution provides cost savings in fabrication and required installation equipment. Furthermore, the foundations are relatively easy and rapid to install and can be positioned with high precision by controlled and simple marine operations, and they can be removed for reuse. This paper describes the use of steel suction piles for deepwater subsea Manifolds, Tie-in Spool Bases and Subsea Control Distribution Assemblies, in the West Delta Deep Marine (WDDM) and Rosetta concessions offshore Egypt. Most of the structures were supported by a single suction pile foundation; pile diameters ranged from 4 m to 8 m and penetrations from 8 m to 12 m. One of the larger units was supported by a “quad” foundation frame with four suction piles. Soils in the area are very soft, normally consolidated clays typical of deepwater conditions. Design is complicated by seismicity of the area, which required the foundations to resist significant horizontal dynamic loads in addition to the normal vertical operating loads. The solution adopted utilized an internal top plate in contact with the soil allowing full development of base bearing capacity. As the pile skin friction in these soils is very low, the increased end bearing leads to significant savings on foundation weight and cost. The paper discusses the main aspects of foundation design, covering the installation process with expected self weight penetration and the required suction to achieve the target design penetration, the retrieval operation for repositioning in case the final inclination is out of tolerance, the assessment of the bearing capacity and the stability under the combined vertical, horizontal and overturning loads during operation and earthquake conditions. Seismic design was based on a nonlinear dynamic analysis. In some cases the seismic loads were comparable to the ultimate foundation capacity and the final acceptance criteria utilized a Performance Based Design philosophy. In this approach the foundation is considered acceptable if the deformation experienced by the structure, during and after the seismic event, does not jeopardize structural integrity.

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