Dynamic model and influencing factors of dust pollution after blasting in high altitude tunnel

In order to reduce the dust pollution caused by drilling and blasting in high altitude tunnel construction, im- prove the dust control technology and occupational health guarantee ability in tunneling face, and promote the clean production level in tunnel construction, the forced ventilation model of tunnel blasting was established on the basis of a working area in southwest railway tunnel, and the dust pollution dynamics model of high altitude tunnel was built according to the gas-solid two-phase flow theory and aerosol mechanics. The numerical simulation software was used to analyze the pollution effect of high-concentration dust in blasting-driven tunnel under different altitudes, ventila- tion distances and ventilation air volumes, and the grey correlation analysis method was used to explore the correlation between the time required for the dust concentration to decrease to a safe value and various influencing factors. The re- sults show that the environmental parameters and the movement characteristics of gas-solid coupling fluid will change with the elevation. The horizontal movement speed of dust particles is negatively correlated with elevation and dust par- ticle size, while the vertical settling speed is opposite. The spatial distribution of dust concentration after tunnel blas- ting at high altitude obeys multivariate Gaussian distribution, and the diffusion coefficient increases with the increase of altitude. The distribution area of wind field in tunnel is divided into vortex area, transition area and stable area. The vortex area is cone-shaped and the wind speed in the center is lower than that in the surrounding area. The average wind speed in tunnel section decreases to about 0. 3 m / s and gradually stabilizes. After blasting, the dust parti- cles move out of the tunnel in a “⊃” shape with the wind, and the dust concentration at the return air side of the tun- nel is higher than that at the air duct side. The large particle dust (particle size ≥30 μm) produced after blasting rapidly settles within 100 m from the tunnel face, and the small particle dust will diffuse with the wind and be suspen- ded in the tunnel space, and the farther the diffusion distance is, the smaller the particle size of the dust will be. With high tunnel altitude, expanding the distance between the outlet of air duct and the tunnel face and increas- ing the air volume of air duct are all beneficial to reduce the dust pollution effect after tunnel blasting. The time re- quired for the dust concentration in the tunnel to decrease to a safe value is most affected by the ventilation distance, followed by the air volume, while the influence of altitude is relatively limited, and its grey correlation coefficient is 0. 684, 0.678 and 0.661 respectively.