Numerical study of the characteristics of smoke spread in tunnel fires during construction and method for improvement of smoke control

In this study, the characteristics of smoke spread in tunnel fires during construction were investigated using numerical modelling. Besides, the method for improvement of smoke control was investigated. The results indicate that the smoke still maintains a good layered structure after hitting the excavation face when the fire is very close to the excavation face. In contrast, the stratification of smoke is destroyed after hitting the excavation face, after which the smoke seems to spread over the entire cross-section of the tunnel when the fire is far away from the excavation face. The construction shaft becomes a common access for natural ventilation and smoke exhaust, which causes the smoke to fill the tunnel quickly because of the large vortex produced by the interaction between the airflow and smoke flow. A drainage device was placed in the middle of the construction shaft to divide the accesses for natural ventilation and smoke exhaust, after which the temperature rise in the tunnel decreases significantly and the mass flow rate of smoke through the construction shaft increases. This study is useful for tunnel fire protection engineering, providing a theoretical basis and technical support for fire detection, early warning, and control in tunnels during construction.