Probabilistic Design of Suction Caisson Jackets Under Sustained Tension Loading

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Suction caisson jackets can offer an attractive solution where alternative foundation types are unfeasible due to soil conditions or other installation constraints. However, these structures can be subject to unique design challenges as the size of wind turbine generators and water depths increase. The ability of the caissons to resist sustained tension loads associated with operational wind loading is becoming increasingly significant for design, and typical deterministic approaches can add significant conservatism to the assessment of this limit state. This paper proposes an alternative methodology to assess the limit state, employing probabilistic reliability-based methods to assess and reduce conservatism in the deterministic approach typically adopted in design. The proposed methodology is applied to a case study from the Seagreen project, where sustained tension is an important consideration when a conventional deterministic approach is adopted. The method is shown to significantly reduce conservatism compared to the deterministic approach. The limit state is first assessed using a simplified approach, considering short duration load and long-duration resistance, but probabilistically, and it is shown that for the design case study the load partial safety factor can be reduced from 1.35 to 1.17, resulting in potential for significant design savings. The limit state is then assessed fully, considering pairs of duration-dependent load and resistance, and further design savings are shown to be possible. The proposed methodology is shown to have significant potential to improve efficiency of suction caisson designs where this load case is governing design.

5th International Symposium on Frontiers in Offshore Geotechnics (ISFOG2025)

11 - Suction installed foundations and anchors