Mechanical Behavior and Bearing Capacity Calculation of Ultra-High Performance Concrete (UHPC)-Reinforced Tunnel Linings

Ultra-High Performance Concrete (UHPC), characterized by its superior mechanical properties and excellent durability, has emerged as a promising material for the repair and reinforcement of tunnels. This study aimed to clarify the reinforcement mechanism of UHPC for tunnel linings and the improvement in bearing capacity through numerical simulation and theoretical derivation. By simulating normal concrete (NC) and reinforced concrete (RC) eccentrically loaded columns under varying reinforcement configurations and working conditions, the study investigated the failure modes and mechanical behaviors of UHPC-reinforced tunnels. Analytical equations for the compression-bending capacity of UHPC-reinforced columns under secondary loading were established and validated. Subsequently, the influence of key parameters was systematically analyzed. The results show that UHPC reinforcement significantly enhances load-bearing capacity, deformation resistance, stiffness, and ductility, albeit with varying failure modes. Notably, the ultimate load-carrying capacity increases by up to 184.6% for NC columns at 180 mm eccentricity and 286.5% for RC columns at 200 mm eccentricity. Reinforcement effectiveness is highly influenced by eccentricity: inner-side reinforcement proves more advantageous under small eccentricities, whereas outer-side reinforcement outperforms under large eccentricities. Comparative analyses of various parameters reveal that initial strain has the greatest impact on reinforcement effectiveness, followed by UHPC thickness, UHPC strength, and the reinforcement ratio of the reinforcement layer, in descending order of influence. The research provides valuable insights into the application of UHPC in tunnel reinforcement, offering a reliable theoretical and numerical basis for engineering design.