Prevention and control of gas hazards in a tunnel under construction: a case study

This paper presents the results regarding the prevention and control of gas hazards in a high-gas tunnel under construction. First, some effective methods were introduced, and the results of the gas pressure and gas content measured with and without the prevention methods were compared. Next, the gas emission amounts were predicted according to the measurements, and the required air volume for preventing a potential gas explosion hazard was determined. Finally, a computational study was carried out to investigate the effects of the transverse and longitudinal outlet locations of the ventilation duct on the gas movement in the tunnel. The results showed that with an increase in the longitudinal distance between the outlet and the heading face, the percentage of dead zones at the heading face of the upper bench increased, while the percentage of dead zones at the heading face of the lower bench observably decreased at first and then increased gradually. Additionally, the maximum methane concentration decreases initially and then increases. The percentages of dead zones were at relatively low levels when the outlet was located at the tunnel vault, whereas some relatively higher percentages of dead zones existed when the outlet was located at the tunnel spandrel or hance. The maximum methane concentration increased gradually when the location of the ventilation outlet moved away from the tunnel axis. In this case, the optimal outlet location for the ventilation duct was suggested to be 20 m away from the heading face of the upper bench and located near the tunnel vault.