Experimental Investigation of the Mechanical Performance of Steel Fiber-Reinforced Concrete Tunnel Linings Under Freeze–Thaw Cycles

Tunnel lining models were cast at a 1:20 scale using four different materials: plain concrete (PC), steel fiber-reinforced concrete (SFRC), reinforced concrete (RC), and rebar-reinforced steel fiber-reinforced concrete (R/SFRC). Loading tests were performed on these models before and after freeze–thaw cycles to investigate the failure modes, analyze the mechanical behavior, and determine the optimal reinforcement scheme in this study. The results indicated that freeze–thaw cycling reduced the load-bearing capacity of tunnel linings by 12% to 28% compared to non-freeze–thaw linings. Adding steel fibers significantly enhanced the ductility of the lining models. The mechanical performance of linings with an optimal steel fiber content surpassed that of models with either increased rebar alone or steel fibers alone. In this study, an optimal combination of a 0.36% rebar ratio and a 1.5% steel fiber volume fraction effectively improved the tensile performance of the lining while reducing rebar consumption, without compromising the inherent mechanical performance of the tunnel structure.