CO diffusion during high-altitude and high-ground temperature tunnel blasting based on field monitoring and numerical simulation

As more complex tunnel projects are being constructed in the mountains of southwestern China, understanding the diffusion phenomenon of carbon monoxide (CO) in high-altitude tunnels is essential. This is particularly critical for tunnels with high ground temperatures during blasting. This study employed field monitoring and computer simulations, focusing on a specific plateau tunnel. A real-time monitoring system was established, using CO as the representative gas. A computational fluid dynamics model was developed and was validated against field data. Results show that forced ventilation could create four distinct flow regions. CO concentration in the tunnel declined during outward diffusion under ventilation. Specifically, the CO concentration was increased by a factor of 1.83 with the increase in the altitude from 0 to 5000 m. Furthermore, with ground temperature rising from 300 to 320 K, the propagation speed of the CO concentration peak accelerated, arriving at the tunnel exit section 53 s earlier, and its magnitude was decreased by 224 ppm. Finally, a functional relationship was established between CO concentration, ventilation time, distance, temperature and altitude. This study provides a valuable reference for safety assurance and informs ventilation design for tunnel construction in relation to CO diffusion in such tunnels.