Study on the Influence of Setting Parameters of Tunnel Centralized Smoke Extraction System on Fire Smoke Flow and Temperature Decay

The centralized smoke exhaust system of shield tunnel is an important determinant for tunnel fire safety, and the use of different design parameters of the tunnel smoke exhaust system will affect the smoke exhaust effect in the tunnel, and the influence of different design parameters on the smoke exhaust effect and temperature attenuation of the tunnel can help engineers in designing a more effective centralized smoke exhaust system for the tunnel. In this paper, the Fire Dynamic Simulator (FDS) is utilized to examine smoke exhaust vent settings for a centralized exhaust system in shield tunnel with both flat and sloped conditions, including slopes of +4.5% and −4.5%, under a 30 MW fire power with a 150 m³/s smoke exhaust rate. The results suggest that maintaining a vent spacing of 60 m and a vent size of 4.0 m × 1.5 m is a reasonable configuration for centralized smoke exhaust systems in both flat and slope shield tunnels. This choice helps minimize construction costs and prevent excessive smoke accumulation. It also promotes favorable conditions for maintaining temperature distribution at 2-m height, visibility, smoke spread distance, and temperature below the ceiling, all below the threshold values, while ensuring high smoke extraction efficiency. However, in the slope section, the chimney effect can disrupt exhaust efficiency, visibility, ceiling temperature, and temperature distribution at a height of 2 m. Employing different opening methods, such as having 2 vents up and 4 vents down in a +4.5% slope and 4 vents up and 2 vents down in a −4.5% slope, can help mitigate these effects. Furthermore, the temperature decay formula for shield tunnels follows a bi-exponential decay pattern, and different design parameters of centralized smoke exhaust systems have minimal effects on temperature decay in shield tunnels.