Understanding Tunnel Lining Deformations: The Influence of Cover Depth on Structural Behaviour

As cities continue to expand, the demand for effective underground infrastructure to address urban transportation challenges has increased. Tunnels, particularly those constructed using the New Austrian Tunneling Method (NATM), play a crucial role in managing these challenges. This study investigates the deformation behaviors of NATM tunnels under three different cover depths (17 m, 26 m, and 56 m) using the Finite Element Model (FEM) under static loading conditions. The main objective is to analyze the impact of varying cover loads on the stability and structural integrity of egg-shaped tunnel geometries, which are commonly preferred by designers. The analysis investigates deformations during excavation, focusing on both tunnel convergence and surface settlement, in a four-layered ground profile consisting of weathered soil, weathered rock, soft rock, and hard rock, respectively. By comparing these deformations under different cover loads, this study highlights critical factors influencing tunnel design and provides valuable insights for ensuring the safety and efficiency of shallow tunnel construction, particularly in multi-layered rock formations. Key findings indicate a maximum vertical displacement of -11.50 mm at the top of the final lining and a maximum compressive thrust of 155 t/m in the deepest case, demonstrating a non-linear structural response to increasing cover depth. The results, supported by graphical representations, demonstrate the importance of precise cover load calculations in tunnel stability and contribute to the development of engineering guidelines for similar projects.