Tunnel ventilation during construction and diffusion of hazardous gases studied by numerical simulations

Proper ventilation of tunnels has remained a serious issue for many years. However, only empirical methods are currently utilised for estimating ventilation time scales in construction scheduling. In this study, the forced ventilation system used in tunnels under construction was investigated through computational fluid dynamics modelling. The effects of influencing factors, such as the duct position, distance between the ventiduct mouth and the working face, air velocity in the duct, and cross-sectional area of the tunnel, were examined, and the flow field and CO concentration distributions in the tunnel space were determined. The obtained results revealed that the zone near the working face can be divided into a jet zone, backflow zone, and vortex zone. Pollutant discharge was strongly related to the flow field distribution. The CO concentration distributions were calculated from the data sets generated by various models, and a ventilation time estimation function was derived for the entire tunnel construction period. The blasting cycle can be significantly shortened by allowing construction workers to enter the tunnel within the calculated entry periods, and necessary construction procedures can be reasonably implemented. The flow field distribution and time dependence of the CO concentration deduced in this study can be extended and applied to other similar projects. •Flow field division near working face through numerical simulation.•Strong correlation between pollutant discharge and flow field distribution.•Influence of multiple factors on flow field distribution and harmful gas emission.•Derivation of distribution function for harmful gases.•Estimated function of ventilation time during tunnel construction.