Study on Load and Structural Force Characteristics of Shield Tunneling in Mountainous Railway

Research purposes：In order to investigate the load distribution characteristics of mountainous shield tunnel and the mechanical behavior of its lining structure，this paper focuses on a specific railway project. Utilizing the finite difference software FLAC3D，a three-dimensional numerical model is established to study the load distribution and magnitude on the segment of the shield tunnel in a large-section mountainous railway tunnel. The paper also analyzes the internal force distribution characteristics of single and double-layer linings under various influencing factors. Research conclusions：（1）The stress in the surrounding rock of the lining exhibits a trend of instant increase，decrease，subsequent increase，and eventual stabilization before and after the shield tunnel passes through. After stabilization，both the vertical and lateral earth pressures on the lining show a distribution pattern with higher values at the ends and lower values in the middle.（2）The tunnel should employ load calculation theories that correspond to its existing conditions. For instance，the Prandtl theory is suitable for a 50 m depth（Class V surrounding rock），while the railway tunnel code theory is suitable for a 100 m depth（Class V surrounding rock）. When the surrounding rock conditions are poorer and the depth is shallower，the results of load calculation theories slightly lean towards being less safe. On the other hand，for greater depths and better surrounding rock conditions，the results of load calculation theories tend to be conservative.（3）In a double-layer lining structure，the secondary lining experiences minimal internal forces compared to the segments. Furthermore，the stability of the surrounding rock significantly affects the stress characteristics of the secondary lining.（4）This research outcome can provide technical support for the structural design of mountainous shield tunneling. © 2024 Editorial Department of Journal of Railway Engineering Society. All rights reserved.