Airflow velocity attenuation characteristics and a zoned dust control method in ventilation for drill-and-blast construction of V-shaped cross-sea tunnels

To address the problem of low dust removal efficiency in long-distance forced ventilation during drill-and-blast excavation of V-shaped subsea tunnels, which is caused by air leakage, along-path frictional resistance, and longitudinal slopes, this study takes the Qiongzhou Strait subsea tunnel project as the engineering background and establishes a wind velocity attenuation and fan pressure head demand model considering slope effects, systematically revealing the mechanisms by which leakage rate, ventilation distance, and longitudinal slope influence the air supply capacity of the ventilation duct. A zoned clean ventilation method based on air curtain isolation is proposed, which effectively separates the contaminated air zone near the tunnel face from the fresh air zone in the downstream section, thereby suppressing the long-distance axial diffusion of blasting dust along the tunnel. The results show that an increasing downward slope reduces the average dust attenuation rate within 15 min from 86.31 mg/min to 57.81 mg/min; for each 1° increase in slope, the ventilation time increases by approximately 6.92% on average. The zoned clean ventilation method can confine high-concentration dust within 100 m of the tunnel face, and at a ventilation distance of 4600 m, the average dust concentration under the zoned clean ventilation mode is only 56.96% of that under conventional forced ventilation. Moreover, this ventilation mode can still maintain effective dust removal at ultra-long distances by extending the ventilation duration. The research results provide a theoretical basis for ventilation design and dust control in V-shaped subsea tunnels.