IN-SERVICE AND LIFTING ANALYSIS OF OFFSHORE PLATFORM JACKET DURING THE DECOMMISSIONING PHASE WITH VARIATION IN SOIL ADHESION LOADS

• Main Author: Adyftha Hawis, Ainun
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/86400
• Institution: Institut Teknologi Bandung

One of the critical stages to be reviewed in the construction of offshore platforms is the Decommissioning phase. In this phase, the platform structure is removed from its existing location using a lifting method. The structure at the mudline, which remains in contact with the seabed, interacts with the soil beneath it. This interaction induces a suction effect at the mudline, significantly increasing the load accumulated at the hook point. This study analyzes the additional loads that arise due to the interaction between the mudmat and clay soil. Clay soil tends to generate suction effects when subjected to axial tensile forces. This research investigates the impact of variations in undrained shear strength of clay soil on soil suction loads and operational loads experienced during the lifting of underwater jacket structures as part of the Decommissioning process. The approach employed in this study is numerical simulation using the finite element method, which allows detailed analysis of various scenarios involving variations in undrained shear strength of clay soil (ranging from very soft to firm). The simulation is designed to evaluate how changes in undrained shear strength influence the distribution of soil suction loads experienced by the structure during the lifting process, as well as how these variations affect the lifting load required to successfully remove the structure from the seabed. The simulation results indicate that variations in undrained shear strength have a significant impact on soil suction loads, where an increase in shear strength generally results in higher suction loads, leading to an increase in the total uplift load generated. For instance, in a simulation conducted on soil with an undrained shear strength of 10 kPa, the required uplift capacity increased to 3.121 times the submerged weight of the structure. This study also assesses the adequacy of the structural members to determine whether the members of the lifted jacket module can withstand the uplift loads during the lifting process. The maximum unity check value is obtained at an undrained shear strength variation of 10 kPa and is located at the jacket leg with a UC value of 0.140.