Abstract:

To study the changes in flow fields and oxygen concentration distribution under different ventilation parameters in high-altitude tunnels and to explore optimization measures, on-site experiments for verification were conducted in tunnels and a computational fluid dynamics simulation model was established. Various oxygen consumption boundaries of the high-altitude tunnel under construction conditions were hypothesized and calculated. The component transport equation was activated to simulate the distribution of oxygen concentration in the TBM tunnel. The influence of different air outlet wind speeds, areas, and oxygen mass fractions on the volume proportion and variation pattern of low-oxygen areas, as well as the causes of the formation of low-oxygen areas were analyzed. The comparison between experimental data and numerical simulation results shows the following: (1) Volume fraction of oxygen concentration in the air drops sharply near the diesel locomotive and exhibits a fluctuating upward trend with the increase of the distance to the tunnel face. (2) When the air outlet wind speed increases from 14 m/s to 20 m/s, the proportion of lowoxygen areas in the tunnel can be effectively reduced and the oxygen concentration in the tunnel can be increased. (3) There is a negative correlation between the area of the air outlet and the volume percentage of the hypoxic zone. As the area of the air outlet gradually increases, the area of the hypoxic zone dramatically increases, and the gradient of oxygen content change at the interface between oxygen-rich and hypoxic also gradually increases. (4) Maintaining the oxygen mass concentration at the air outlet at 0.275 kg/m³ can ensure an oxygen volume fraction higher than 20%, meeting the requirements of high-altitude tunnel construction.

Key words: high altitude, TBM, tunnel air flow field, oxygen distribution characteristics, computational fluid dynamics simulation