| A large amount of dolomite is distributed underground in Guizhou,China.When the cantilever boring machine is used in the construction of the narrow and small section hard dolomite subway tunnel,the area near the working face is often affected by high concentration of dust pollution.When the cantilever boring machine drives hard dolomite into the tunnel face of the subway tunnel,the boring machine bit presses against the rock wall and keeps rolling.The pick on the bit grinds the tunnel face,and the whole tunnel face rock wall is grinded out of the grooves and lithosphere of concentric rings.The atomizing system of the roadheader is mainly used to cool the drill bit of the roadheader which rotates at high speed during construction instead of dust removal.Moreover,the arrangement of the nozzles is semi-circular,so the droplets field formed cannot wrap the concentric ring of the drill grinding closely,causing a large amount of dust to escape,so the dust removal effect is not ideal.Based on the background of the subway tunnel between Huaguoruo East Station and Huaguoruo West Station of Guiyang Metro Line 3,this paper uses theoretical analysis,field measurement,numerical simulation,model test and field application to investigate the dust diffusion law generated by cantilever boring machine in the process of subdivision tunneling,and proposes a dust-removal device at the end of the boring machine to effectively reduce the dust concentration in the subway tunnel.The main work done is as follows:(1)By measuring the concentration of in-situ driving dust and collecting the driving dust to study the distribution characteristics of the concentration and particle size of the cantilever driving dust in the metro tunnel,combined with FLUENT numerical simulation software,the axial and radial diffusion law of the dust generated during the driving in the air flow field,working surface and lower zone was further explored.(2)Through the model experiment platform,the atomization Angle,range and flow rate of four kinds of nozzles,such as wide-angle solid conical nozzle with diameter of 1.9mm,standard solid conical nozzle with diameter of 1.8mm,standard solid conical nozzle with diameter of 1.2mm and fine solid conical nozzle with diameter of 1.6mm,as well as the overall atomization dust removal rate,are compared and selected.The nozzle with the best comprehensive dust removal efficiency was installed on the U-shaped dust removal device for follow-up research.(3)Numerical simulation using fluid dynamics(CFD)calculation method,it was explored that the droplet field formed by the U-shaped spray device could tightly wrap the cutting head.7,9 and 11 nozzles were set on the U-shaped tube,respectively.The covering range,spray concentration,spray velocity and particle size of the droplet field under different spray pressures were analyzed,and the nozzle setting method with the best comprehensive dust removal performance was selected.(4)Through field application,dust concentration before and after U-shaped dust removal device is measured,dust removal efficiency of total dust and respirable dust is analyzed,and dust removal effect of U-shaped dust removal device is tested.Under the four pressures of 2,4,6 and 8MPa,the wrapping property,the optimum droplet size and the optimum spray field concentration are analyzed to determine the optimal spray pressure.When the number of nozzles is 11,the droplet field has the best wrapping property.Under the spray pressure of 8 MPa,the particle size of more than 90% of the droplets in the spray field is between 30～100 μm,and the particle size distribution of the droplets is more uniform,and the dust suppression performance is better.When the spray pressure is 8 MPa,the proportion of high concentration droplets is more than 70%,and when the number of nozzles is 11,the proportion of high concentration droplets on the palm surface reaches the maximum77.36%.Through the field application,the maximum total dust suppression efficiency reached 81.41%,the maximum respirable dust suppression efficiency reached 80.59%,the other monitoring sites were also above 70.46%,the dust suppression effect is obvious. |
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