Numerical Study of Construction Ventilation in the Diversion Tunnels with Long Vertical Shafts

Ventilation during shaft construction is one of the key issues in the construction process of tunnel projects. In this study, numerical simulation is conducted to investigate the ventilation during the construction period of a diversion tunnel project containing deep shafts. The distribution laws of the flow field and CO concentration field at the junction of the shaft and the flat tunnel are analyzed. The CO concentration under different time periods was also quantified and analyzed, and the CO distribution law at the typical location of the shaft was obtained. The influence mechanism of vertical cross structure and air pressure difference on the ventilation of the shaft during the construction period was investigated. The results show that there are obvious vortex zones at the intersection of the shaft and the flat tunnel, and at the lower part of the shaft expansion section, which can seriously affect the ventilation efficiency during construction. The transport diffusion of CO is closely related to the structure of the tunnel. The flow field and the distribution law of harmful gases derived in this study can be extended to other similar projects.