Pattern characterization concerning spatial and temporal evolution of dust pollution associated with two typical ventilation methods at fully mechanized excavation faces in rock tunnels

In order to understand the temporal and spatial evolution pattern of dust pollution under blower and long-compression short-suction (LCSS) ventilation conditions at fully mechanized excavation faces in rock tunnels so as to effectively enhance dust removal efficiency, the present study conducts numerical simulation on the airflow field and dust dispersion associated with these two ventilation methods. The results indicate that the airflow pattern under the blower ventilation method is primarily dictated by the compressive jet field. The LCSS ventilation method leads to a continuous vortical airflow field, which makes the corresponding average dust concentration at fully mechanized excavation face lower than its counterpart associated with the blower ventilation method. The dust concentration roughly stabilizes after 193 s and 244 s for the LCSS and blower ventilation methods, respectively; due to the suction effect at the suction inlet at the front, the average dust dispersion velocity of LCSS ventilation method is lower than that of blower ventilation method, and it takes 141 s and 121 s to disperse dust to the tunnel outlet for the LCSS and blower ventilation methods, respectively. Despite the fact that the LCSS ventilation method is superior to the blower ventilation method, it still fails to deliver an effective dust control. The accuracy of the numerical simulation results is corroborated by field experiments. Furthermore, numerical simulation study is conducted to examine the impact of Lp (i.e., distance between compressed airflow outlet and heading end) for a range between 5 m and 50 m. It is found that for Lp < 30 m, the airflow field is fairly turbulent without forming an air curtain for dust control, which makes the dust dispersion reach the entire tunnel; for Lp > 30 m, a dust-control air curtain is established at the heading machine driver's location, and the dust-control effect of air curtain is improved as Lp increases from 30 m to beyond 35 m. When Lp increases above 35 m, the dust is effectively confined within a space upstream of the driver's location (<5.5 m away from the heading end).