| During the construction of tunnel drilling and blasting method,a great deal of dust will be produced,eapecially the instantaneous value of dust concentration after face blasting can reach several thousand millgrams per cubic meter.This situation not only deteriorated the working environment,but also caused great harm to the physical and mental health of the construction workers.The workers are very vulnerable to pneumoconiosis in the high concentration dust working environment for a long time.At present,the experts and scholars put forward many kinds of measures,such as stemming the dust,spray and aspirating,et al.but environmental conditions in the tunnel is still very bad even if the technical measures taken in the construction process,especially after blasting and ventilation a long time the dust concentration is still difficult to control within the industry standard of our country's rules.It can be seen that the study of effective dust control measures is the objective demand of construction work,but also the inevitable trend of civilized construction.Therefore,this dissertation carry out the technique of using air curtain jet dust and dust removal equipment method to suppress the dust removal technology joint operations spread from the theoretical analysis,field measurement and modeling experiments and numerical simulation,in order to compressed dust removal time,improve the efficiency of dust removal.The main research contents and conclusions of this dissertation are as follows.1.The problems existing in the present situation of main dust control technical measures are found out through sorting out the present situation of theoretical research and numerical simulation analysis of dust control in construction tunnels at home and abroad,.At present,the main technical measure for dust control focus on emission rather than concentration,there is a common problem of low dust reduction efficiency.From the point of view of dust protection,the isolation and dedusting by air curtain ventilation was put foeward,which has solved the problem of dust diffusion in tunnel and achieved the goal of improving the construction environment.2.The airflow vector characteristics and dust concentration evolution law in tunnel under forced ventilation mode were obtained through on-site monitoring of ventilation environment in Xiaofanping tunnel construction.The measured results show that the farther the turbulence is from the working face,the more stable the wind speed is,and the unsteady motion in longitudinal reflux,dust discharge has pistion characteristics.The relative dust removal rates on working face,both sides of lining shutter I and inflected arch were over85%after 60 mins of ventilation,and dust removal efficiency at other section was relatively low.Especially,the reative dust reduction rate on both sides of lining shutter II was not more than 65%.The peak dust concentration in the construction area was 38.7 mg/m~3 and the average dust concentration in the longitudinal direction in tunnel was 23.38mg/m~3.3.The construction of air curtain method of ventilation mode in construction tunnel was put forward according to the analysis of the jet flow theory,the movement process,the velocity distribution and flow attenuation characteristics of jet flow were analyzed,the distribution flow of motion and the characteristics of flow distribution are discussed according to the size of the angle between jet axis and tunnel section.4.The similarity experiment was carried out on the dust removal effect of air curtain ventilation equipment in the tunnel model of Xiaofanping tunnel,the optimal setting angle,width and wind speed of the air curtain nozzle in the similar model was determined.The experimental results show that the main factors affecting the dust isolation effect were the width of the jet nozzle,the initial velocity of the jet and the jet angle.Large-angle oblique impinging flow under external negative pressure will lead to offset on tunnel floor,if the wind speed is unstable during ventilation,the dust will pass through the air curtain to pollute the clean area.The experimental results confirm that the optimum width of jet nozzle in the similar model was 5mm,the optimum speed of jet on the wall was 6m/s and the optimum setting angle of jet was 30°.Meanwhile,regression analysis was carried out on the relevant parameters in Xiaofanping tunnel according to the optimal experimental parameters of the similarity modeling model,which providing data support for Fluent numerical simulation.5.The forced ventilation and air curtain ventilation were established by Ansys-fluent,a fluid dynamics analysis software.Moreover,the characteristics of flow field,dust evolution characteristics and dust removal efficiency of the two models were compared and analyzed,and the high efficiency of dust removal under the air curtain ventilation was verified.The simulation results show that the dust concentration in the polluted area reached the standard after 60mins of ventilation and the dust concentration in the clean area reached the standard after 30mins of ventilation under air curtain ventilation,however,the dust concentration in the construction area is still very high and fail to meet the standard after under forced ventilation after 60mins of ventilation.After 30 to 60mins of ventilation,the air curtain ventilation mode was significantly higher than that of forced ventilation mode,and the absolute dust reduction rate of air curtain ventilation mode was close to 100%after 60mins of ventilation. |
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