Numerical Study of the Effect of Heating Rate on the Thermo-Hydro-Vapor Behavior and Damage Mechanism of Tunnel Lining Concrete

The effects of heating rate on heat and mass transfer, as well as damage mechanism of lining concrete, were investigated using a coupled thermal-hydro-vapor finite difference model. The results showed that during a steady thermal state, the surface temperature depended solely on the peak temperature, and was independent of the heating rate. Vapor pressure exhibited pronounced nonlinearity. At low heating rates, its peak increased monotonically with depth. Whereas at higher heating rates, peaks appeared earlier and followed a two-stage distribution-initially increasing and then decreasing with depth. Within the first 20 mm of depth, the heating rate had a substantial influence on heat transfer, moisture migration, and phase changes. However, beyond 50 mm, its effect was negligible. Concrete damage was predominantly governed by thermo-mechanical processes, which accounted for more than 80% of the total damage. At higher heating rates, this proportion increased to approximately 90%, underscoring the growing dominance of thermo-mechanical effects. To maintain the structural integrity of tunnel linings, the heating rate should be limited to below 50 °C/min.