Installation and Levelling Structural Analysis for Underwater Jacket Structure (RSS Tower)

Abstract The objective of this study is to evaluate the structural integrity and operational feasibility of levelling an underwater jacket structure—Riser Support Structure (RSS) Tower—with four skirt piles on the seabed. The analysis focuses on achieving installation tolerances by correcting an initial inclination of approximately 1°, ensuring safe load transfer to piles while maintaining structural and geotechnical stability. A multi-stages structural analysis simulates the transition from initial seabed contact to full pile engagement using SACS. Soil–structure interaction (suction forces, frictional resistance, and environmental loads) is included. Six stages apply incremental pulling forces at the lowest leg to achieve horizontal alignment. Soil springs, pile grippers, and lateral restraints reflect realistic offshore conditions. Lock-in stresses and pile reactions are monitored to ensure compliance with allowable stress and capacity limits. Levelling up to 1° is feasible: maximum member UC ≈0.99 and joint UC ≈0.88 at Pile A2; highest pulling force ≈292 MT; final pile reactions within allowable limits with safety factors ≈2.32 (operating) and ≈1.86 (storm).