Spray dust control measures of tunnel blasting dust based on CFD dust-droplet coupling model and orthogonal test

In extra-long tunnels, the dust generated by blasting excavation is difficult to discharge through ventilation, which can easily lead to secondary dust generation, severely affecting the health of construction personnel inside the tunnel and potentially increasing the construction interval. To shorten the dust removal time and enhance efficiency during tunnel blasting, this study utilized a single-hole single-track railway tunnel to conduct on-site measurements and numerical simulations of blasting dust. The effectiveness of the dust mist coupling model was validated through indoor model experiments, showing a maximum deviation of 16.94 % between the average concentration at numerical simulation monitoring points and that from model test measurements. Additionally, the model's stability was assessed using three grid sizes: coarse, medium, and fine, with the maximum relative change in dust removal rate reaching 14.75 %. In combination with the original forced ventilation system, a three-section spray dedusting method was designed. The first nozzle was positioned at the center of the forced air duct outlet, with a nozzle diameter of SH2.4 mm. The second section, located 50 m from the tunnel face, contained two nozzles placed at the top and bottom of the section. The third section, situated approximately 100 m from the tunnel face, featured two X-core circular nozzles with a diameter of 2 mm, operating at a spray pressure of 8 MPa. Nine groups of orthogonal experiments were designed using CFD, identifying the spray angle, compressed air duct volume, and spray ring spacing as the most influential factors in dust removal time. Through the addition of Experiment 10 to the orthogonal set and subsequent comparisons, the optimal spray parameters were determined to be a spray angle of 15 degrees, a compressed air duct air volume of 26 m3/s, and a spray ring spacing of 50 m. Based on the analysis of numerical results, it can be concluded that the spray dust reduction measures effectively reduced the dust concentration within 200 m of the tunnel face to a safe level 900 s after blasting.