Study on CO diffusion law and concentration distribution function under ventilation after blasting in high-altitude tunnel

Abstract

Multiple toxic gases, such as carbon monoxide (CO), are generated after blasting of plateau tunnel. To study the influence of high-altitude environment on the diffusion and concentration distribution of hazardous gases after tunnel blasting, a ventilation model for construction tunnel was established based on a tunnel of the Sichuan-Tibet Railway, and the dynamic diffusion of CO at different altitudes was numerically simulated. The obtained results demonstrate that: In the area near the working face with forced ventilation, a vortex area was formed under the combined action of jet and backflow, the distribution of CO in the tunnel was closely related to the flow field. The CO migrated to the outside of the tunnel due to ventilation, and was gradually diluted and diffused in the process. The equivalent mass concentration of CO in the tunnel increased exponentially with the increase of altitude, the altitude correction coefficient of CO mass concentration was e0.1H at an altitude of H (km), the concentration value increased by 88% when the altitude rose from 0m to 6000m. To directly obtain the CO concentration value in the construction tunnel under different conditions by calculation, the functional relationship between the CO concentration after blasting and the time (t), distance (x) and other parameters was determined according to the simulation results, and the calculation function was verified by considering field data. The fitting function has wide applicability and can be used to judge whether the environment in the tunnel has reached a safe state, thus providing guidance for the safety of plateau tunnel construction.