A hybrid ventilation scheme applied to bi-directional excavation tunnel construction with a long inclined shaft

The breakage and bending of ducts result in a difficulty to cope with ventilation issues in bi-directional excavation tunnels with a long inclined shaft using a single ventilation method based on ducts. To discuss the hybrid ventilation system applied in bi-directional excavation tunnels with a long inclined shaft, this study has established a full-scale computational fluid dynamics model based on field tests, the Poly-Hexcore method, and the sliding mesh technique. The distribution of wind speed, temperature field, and CO in the tunnel are taken as indices to compare the ventilation efficiency of three ventilation systems (duct, duct-ventilation shaft, duct-ventilated shaft-axial fan). The results show that the hybrid ventilation scheme based on duct-ventilation shaft-axial fan performs the best among the three ventilation systems. Compared to the duct, the wind speed and cooling rate in the tunnel are enhanced by 7.5%-30.6% and 14.1%-17.7%, respectively, for the duct-vent shaft-axial fan condition, and the volume fractions of CO are reduced by 26.9%-73.9%. This contributes to the effective design of combined ventilation for bidirectional excavation tunnels with an inclined shaft, ultimately improving the air quality within the tunnel.