Numerical Analysis of Load Bearing Capacity of Offshore Jacket Platform with Suction Caisson: Fid-Bau Portal

Numerical Analysis of Load Bearing Capacity of Offshore Jacket Platform with Suction Caisson

Cheng, Yongjin / Ge, Xiangming / He, Ben / Zhou, Yong

In Zhuanghe wind farm project II, located in the northeast of China, the load-bearing capacity of 30 offshore jacket platforms with suction caisson has been numerically verified. As a representative, foundation 15# is selected to show the surrounding soils' deformation, rotation, and plastic areas. Various calculation cases have been considered, including the operation state (SLS and ULS), extreme wave load, ice load of a 50-year period, different load directions, and 2 m of scour depth. Calculation results show the influence of ice load in a 50-year period is dominant, in which case the plastic area of ice load cases is way larger than extreme wave load cases. The icing on the near coastline happens a lot in winter, so the effect of the ice load should be carefully treated. The rotation of the 15 # jacket-suction caisson foundation reaches 7.58%o in SLS, which largely exceeds the limit of 4.36%o, so the design 15 # jacket-suction caisson foundation hardly meets the requirement. In this case, the design should be modified and load bearing behavior of structures should be re-verified. Overall, the standard of verifying the loading bearing capacity regarding offshore jacket platforms with suction caisson is that pile top rotation 4.36%o and the plastic area connecting. The suggestion for the design regarding this type of offshore foundation, when the load-bearing capacity is not enough, is to make the suction caisson larger or longer. Also, the accuracy of CPTu representation is crucial for the calculation. Meanwhile, in this study, the pressure difference between the suction bucket inside and outside has not been taken into account, which may cause inaccuracy, and this could be future complimentary research.