Research On Dust Control Technology During Metro Tunnel Construction

With the development of economy in our country,the scale and quantity of city rail transit construction are increasing.Besides,the pollutants generated during subway construction have critically affected the health of construction workers.With the development of the national sustainable strategy and enhancement of people’s awareness of environmental protection,air pollutants have become more serious.More and more attention has been paid to the treatment of pollutants during the construction of subway tunnels.This thesis focuses on control tunnel pollutants base on a Beijing subwayFirstly,the common pollutants in subway construction were monitored,and it was found that the total dust,breathing dust and welding fumes and other dust pollution levels exceeded the standard.Then the PM₁₀ and PM_2.5 distribution law of three working conditions of earth excavation,grid erection and anchor shotcrete was studied during the initial support stage of excavation.The results show that the PM₁₀ and PM_2.5concentration produced by shotcrete is the largest,of which PM₁₀ concentration range is 25.7～31.3mg/m~3,and the PM_2.5 concentration range is 17.2～28.9mg/m~3.The dust particles were sampled and analyzed by particle size and SEM.The particle size with the highest volume percentage of anchor spray dust was 3～4μm,accounting for 14.5%of the dust particles.The welding dust particle size range is 0.8～3μm,and the particle size percentage is 1.4～1.6μm,which accounts for 15.7%.The dust particles near the anchor sprayer have a large particle size,but the surface is not smooth,and most of them are aggregated by small particles.By computational fluid dynamics,the overall construction phase of the subway was modeled in three dimensions and the particle diffusion law of different anchor spray machine construction positions was simulated.The DPM（Deformable part model）model was used to simulate the particle phase movement,the particle is difficult to diffusion in position 4 of side construction.3D modeling for the initial support stage of subway excavation was built,then the press-in and with-out ventilation methods were simulated,the best placement of press-in ventilation ducts at a distance of 20m from the construction surface,and withdraw-out ventilation.The best place to set the pipe is5m away from the construction surface.In view of the serious pollution of the anchor spray working condition,the dust removal device of the anchor spray machine was designed.The device mainly includes two parts:one part is a dust cover,and the other part is a flat bag dust collector.After design of the flat bag filter,then use computational fluid dynamics to analyze the effect of the internal dust removal device,select 6 air inlet positions,of which the center position 5 is the best.In a short period of time the dust removal efficiency is higher than other air inlets.In 60 seconds,the dust removal efficiency is 71.53%.and the dust removal efficiency is 96.5%in 300s.At the same time,chemical dust suppressants are used to remove dust in response to soil dust pollution during earth excavation.Basing on the single-factor experiment design of wind speed,particle size and dust suppressant concentration.The results show that the influencing effect is wind speed,particle size,and dust suppressant concentration in descending order.The wind speed is 4m/s,the particle size is 180 mesh,and the dust suppressant concentration is 3.08‰is the best condition for each factor.The mechanism is mainly bonding.This paper provides an experimental basis for the treatment of common subway tunnel pollutants through the monitoring of subway construction pollutants and the analysis of the characteristics of dust particles.The method of numerical simulation is used to study the subway construction dust at different stages,which provides a certain theoretical basis for the ventilation and dust removal of subway construction.The designed dust removal device of the anchor spray machine has certain guiding significance for the research of reducing the pollution of the anchor spray machine.The factors influencing the effect of dust suppressants are explored,which has certain reference significance for the application of dust suppressants in the process of earth excavation.