For the two lower tunnels, the wind speed ratio varies from 1.51 to 2.02, with a mean value of 1.81 for tunnel-1 and 1.79 for tunnel-2.. By contrast, the wind speed ratio for the two upper tunnels ranges from 1.59 to 2.37, with a mean value of 1.97 for tunnel-3 and 2.05 for tunnel-4. This can be ascribed to the dependence of wind speed with height within the atmospheric boundary layer.