This thesis presents a study on the impact of soil thickness variability on secondary consolidation of overconsolidated glacial soils beneath immersed tunnel elements, specifically focusing on the Fehmarnbelt Tunnel. The research employs a combination of analytical models, including the Timoshenko beam on Kerr foundation model (TBKF model), the Conte and Troncone method and the Feng et al. method, to analyze the initial, primary, and secondary consolidation phases, respectively. It contributes to a better understanding of the behavior of the soil beneath immersed tunnels and informs more accurate predictions and designs in future projects.