A Novel Approach for the Optimization of Segmental Linings in TBM Tunnels through Steel Ring Reinforcement

The escalating demands of global urbanization necessitate efficient and robust underground construction methods, with Tunnel Boring Machines (TBMs) being the predominant choice. The long-term performance of these projects heavily relies on the efficacy and structural reliability of precast concrete segmental lining systems. Despite their advantages, these linings are susceptible to critical structural weaknesses, such as high stress concentrations at joints and excessive deformations in challenging ground conditions. While reducing segment thickness offers sufficient economic and environmental benefits (material saving and reduced excavation diameter), it inherently compromises structural stiffness and safety margins. This study investigates the potential of internal steel rings as a supplementary reinforcement strategy to enhance the mechanical performance of thinner segmental linings, drawing conceptual inspiration from the successful application of steel support systems in the New Austrian Tunnelling Method (NATM). A comprehensive numerical comparative analysis was conducted using the PLAXIS 3D Finite Element Method under challenging rock mass and high overburden conditions. Three distinct tunnel lining models were simulated: a 25 cm reinforced concrete segment lining (Model 1), a 40 cm reinforced segment lining (Model 2), and a 25 cm reinforced concrete segment lining with strategically placed steel rings (Model 3). The analysis focused on Key Performance Indicators (KPIs), including total deformation, N ₂ axial forces, Q ₁₂ shear forces, and M ₁₁ bending moments, and validated the structural safety using N-M interaction curves. The results demonstrate that the integration of steel rings successfully promotes a more favourable redistribution of internal forces, significantly reducing the critical bending moment M ₁₁ demands on the concrete segments. Crucially, the numerical findings confirm that thinner 25 cm segments, when supported with steel rings, achieve structural performance levels comparable to, or even superior to, conventional thicker 40 cm segments, while maintaining a substantial safety margin as verified by the N-M interaction diagrams. This research validates a structurally robust and logistically efficient approach for material optimization, offering considerable potential for both economic and structural improvements in TBM tunnel design and aligning strongly with sustainable construction principles.