The temperature field characteristics of highway tunnels during fire conditions are investigated in this paper. Numerical simulations coupled with reduced-scale physical model tests were conducted to analyze the thermal characteristics of the tunnel interior and lining structure under various ventilation conditions. Taking the extra-long double-tube highway tunnel as a case study, a numerical model was established using FLUENT to simulate a 100 MW fire under different longitudinal ventilation velocities. Furthermore, a reduced-scale physical model with a geometric similarity ratio of 1:2.7 was fabricated to investigate the effect of lining moisture content on the heat transfer characteristics. It is indicated by the results that high-temperature zones above 800 °C are mainly concentrated within roughly 100 m of the fire source, extending approximately 20 m upstream and 80 m downstream. As the ventilation velocity rises, the high-temperature zone adjacent to the fire source is gradually reduced, the upstream smoke backflow length is shortened, and the downstream thermal influence range is expanded. Obvious spatial variations are observed in the cross-sectional temperature distribution: relatively uniform temperatures are found near the fire source, whereas higher temperatures are observed at the crown in upstream and downstream sections, followed by the haunch and sidewalls. A pronounced thermal lag effect is observed in the lining structure, with both slower heating rates and lower peak temperatures being exhibited at larger distances from the fire source and in linings with higher moisture content. A temperature plateau at around 100 °C is detected, which is mainly attributed to latent heat absorption during moisture evaporation. A more significant temperature gradient through the lining thickness is also caused by a higher moisture content. These findings provide valuable references for tunnel fire safety design, smoke control strategies, and evacuation safety analysis.
Ji et al. (Fri,) studied this question.