Model test and application of a side-blowing air curtain system during tunnel construction period in cold regions

During winter construction in these areas, when the environment temperature inside the tunnel drops below 5 °C, it significantly impacts the quality of concrete work. Traditional methods of heating tunnels, such as using stoves, can lead to the production of harmful gases like carbon monoxide. Additionally, the ‘cold door’ approach, while reducing heat loss, can compromise air quality inside the tunnel when insulation is deactivated. Ensuring effective thermal insulation while maintaining adequate ventilation poses another challenge. This paper proposes a balanced approach to safety and thermal insulation effectiveness using an air curtain insulation method, based on the ongoing construction of the Shangshan Tunnel in China. Through on-site testing, the research aims to investigate how different methods—cold door, cold door with stove, and air curtain insulation system—affect the temperature distribution within the tunnel. The findings indicate that the cold-proof door is suitable for tunnel openings where the average wind speed does not exceed 3.21 m/s and the temperature remains above −12.68 °C. The combination of the cold-proof door with a furnace is suitable for tunnel openings with an average wind speed not exceeding 5.36 m/s and a temperature not lower than −19.13 °C. When the maximum wind speed at the tunnel opening is 4.56 m/s and the minimum air temperature is −15.83 °C, an air curtain heat preservation system can be implemented to maintain the cave temperature at 7 °C. During concrete pouring, the air temperature is maintained at 7 °C. With a maximum wind speed of 4.56 m/s and a minimum air temperature of −15.83 °C, the temperature at the poured concrete reaches 7.36 °C. Further improvement in cave air temperature can be achieved by appropriately increasing the jet wind speed or temperature of the air curtain machine, thereby reducing system energy consumption. It is recommended to adjust the air curtain machine's jet wind speed accordingly. The research findings on innovative air curtain insulation technology applied to winter tunnel construction in cold regions provide valuable references and practical guidance for addressing insulation challenges in cold tunnel construction projects.