The influence of tunnel aspect ratio on the gas temperature distribution in advancing tunnel

With the acceleration of underground space engineering construction, the number of advancing tunnels featuring a single-portal during construction is steadily rising, and fire accidents occur frequently. The objective of this research is to comprehensively investigate the decay of flue gas temperature beneath the ceiling of advancing tunnels using theoretical analysis and simulations. The study clarifies the distinctions in smoke movement between an advancing tunnel and a typical tunnel. The results indicate that the mass flow rate of smoke and flow velocity of air near the port are greater when the tunnel has only one open port. As the diffusion distance increases, the thickness of the smoke layer increases, and the gas temperature decreases exponentially under the current research conditions. Holding the tunnel's cross-sectional area constant, the larger the aspect ratio (AR) is, the larger the contact area between the smoke and the tunnel wall as well as the cold air is, resulting in a faster temperature decay of the smoke. Moreover, The empirical models are formulated to forecast the maximum temperature rise and longitudinal distributions of gas temperature. The temperatures, obtained from simulations and experiments, are compared with the temperatures predicted by models, demonstrating the models' accurate predictive capabilities. The empirical model of temperature longitudinal distributions effectively depicts the longitudinal temperature decay process of fire smoke in advancing tunnels, considering various cross-section shape. These findings provide essential guidance and technical support for the implementation of fire suppression systems in advancing tunnels, as well as for the optimization of firefighting procedures during tunneling activities.