Effect of Lateral Soil Strength and Stiffness on Jacket Foundation Integrity and Design for South China Sea Sites

Petronas Carigali Sdn Bhd (PCSB) manages about 150 existing platforms at various sites across South China Sea. Integrity reassessment on these existing structures using non-linear pushover analyses has frequently indicated lateral foundation failure at collapse. However to date there has been no physical observations of foundation failures. Foundation design and integrity assessment takes into consideration lateral soil properties to determine the adequacy of structure-foundation combined system. Observation on Gulf of Mexico foundation performance during hurricane events provided PCSB with the insight and motivation to recalibrate both static and cyclic lateral p-y characteristics of soil currently seen to be conservative. PCSB together with Norwegian Geotechnical Institute (NGI) undertook a study incorporating literature reviews, review of field lateral load data and numerical modeling to recalibrate API RP2A static and cyclic p-y data and derive new modified p-y relationships to suit Malaysian conditions. Further three(3) platforms were reanalyzed using current API RP2A p-y equations and newly modified p-y equations to study the impact of the recalibration made. Result indicates that the modified static p-y resistances provide positive global improvement to pushover analyses. This improvement provides a better justification for the life extension of the existing structures as required in an enhanced loading scenario. Minor to negative improvements are seen when the modified cyclic p-y resistances were used for the purpose of in-place analyses. This paper will focus on the methodology adopted, assumptions and philosophy that form the basis of the recalibration and development of the modified p-y method. Discussion on results of in-place and pushover analyses will be made to provide recommendations on the further use of modified static and cyclic p-y calculation method.