Influence of different air supply modes on dust in bolting and shotcreting operation in construction of metro tunnel pilot tunnels by bench method

In order to effectively control the influence of high concentration dust in the bolting and shotcreting operation in the construction of metro tunnel pilot tunnels by bench method on the health of operators,this study uses field sampling and numerical simulation to analyse the impact of the air duct installation position,the distance between the vent and the tunnel face,and the wind speed in the air duct on dust diffusion,and studies the dynamic changes of dust concentration in the breathing area of operators to determine the best ventilation scheme.The results show that the high concentration dust on site is due to the countercurrent phenomenon inside the tunnel,and the dust collects on the front side of the lower steps.The average dust contact mass concentration of operators exceeds 500 mg/m3.When the distance between the vent and the tunnel face increases to 20 m,the dust mass concentration is reduced by 150 mg/m3.If the wind speed in the air duct increases to 15 m/s,the local dust reduction rate reaches more than 50%.When the air duct is located at the bottom arch and the wind speed increases to 15 m/s,the local dust reduction rate can reach 51.92%,which can achieve the best dust suppression performance.In addition,individual protection and environmental purification and dust removal measures need to be taken on site to reduce dust pollution.