A Numerical Study on the Smoke Diffusion Characteristics in Tunnel Fires During Construction Under Pressed-In Ventilation

Pressed-in ventilation provides the possibility of implementing fire smoke control in tunnels during construction. In this study, the impact of the velocity at the air duct outlet, the heat release rate (HRR), and the tunnel geometry on the longitudinal temperature decay of the ceiling (ΔT) and smoke’s back-layering length (SBL) is investigated, using a reduced-scale experiment and the Fire Dynamics Simulator (FDS, version 6.7.6). The results indicate that an increase in the velocity at the air duct outlet and a decrease in the HRR lead to a reduction in the value of both ΔT and SBL in the main tunnel. Predictive models for the dimensionless longitudinal temperature decay of the ceiling and the dimensionless SBL are proposed. Near the fire source, the predicted SBL is relatively high due to thermal radiation. The research results provide valuable references for preventing tunnel fires during construction.