Full-scale experimental investigation of progressive failure characteristics and failure mechanisms of hybrid fiber-reinforced concrete (HFRC) lining with reduced reinforcement ratio

Hybrid fiber-reinforced concrete (HFRC) has the potential to reduce conventional reinforcement in shield tunnel linings while maintaining structural performance, thereby providing a possible pathway toward lower-carbon segmental linings. However, full-scale experimental evidence on the mechanical performance of low-reinforcement HFRC linings under full-ring constraint remains limited. To address this issue, this study conducted a full-scale loading test on an HFRC tunnel lining with a 50 % less conventional reinforcement than that used in the reinforced concrete (RC) design. The test simulated operational loading, surcharge loading, and horizontal unloading conditions for a staggered-joint lining ring. The results show that the lining satisfied serviceability requirements under operational loading, with no visible macrocracks observed even under surcharge loading. Lateral convergence exhibited three stages of elastic, elastoplastic, and plastic response, accompanied by progressive cracking and internal-force redistribution. At the ultimate state, failure was concentrated at longitudinal joints and critical segment sections, characterized by plastic hinges and concrete crushing along the extrados. The relatively low local stiffness and large deformation capacity of the joints facilitated circumferential bending-moment redistribution, thereby transferring part of the structural demand from the joints to adjacent segments. These results provide full-scale experimental evidence for the structural feasibility and progressive failure mechanism of low-reinforcement HFRC segmental linings.