Air flow and gas dispersion in the forced ventilation of a road tunnel during construction

Abstract

Forced ventilation is typically used in the construction of tunnels since it is an economical method to provide high amounts of fresh air. Air velocity and pollutant concentration near the work face are determined by the ventilation arrangement. In the study, field measurement of air velocity was performed, and computational fluid dynamics (CFD) models were constructed to investigate airflow near the work face and predict the gas distribution in a gas tunnel construction. The effects of the distance between the air duct exit and the work face (L1) were evaluated by analyzing the flow field and pollutant concentration. The evaluation shows that the ventilation efficiency improves if L1 does not exceed 15 m in a road tunnel with full-face excavation. With respect to a road tunnel with benching excavation, the effects of bench length (L2) are analyzed, and the results of the analysis indicate that ventilation efficiency is optimal when L2 = 5 m and L2 = 10 m and the air-duct diameter corresponds to 1.6 m. The CFD results fit the field measurement significantly well, and the current ventilation system in the construction exhibits a relatively high efficiency. The findings of the study aid practitioners in optimizing ventilation efficiency. Keywords: Tunnel construction, Forced ventilation, Ventilation arrangement, Fluid field, Hazardous gases, Numerical simulation