| Recently,with the continuous deepening of the national“One Belt,One Road”strategy,China's transportation infrastructure has developed rapidly,gradually moving from the plain area to the mountainous area.However,as an indispensable part of the infrastructure,the mountainous highway tunnel project is growing in mileage and the scale of construction is expanding.In order to build an environment-friendly society,the air environment in cave has been widely concerned by scholars in the engineering industry.Based on the project of CTM mountainous highway tunnel,this paper carries out further research work from theoretical analysis,on-site inspection,indoor comprehensive test,numerical simulation analysis and quantitative analysis.The results are as follows:(1)Starting from the quality factors which are affecting the construction environment of the CTM mountainous highway tunnel,the CO concentration,dust concentration,environmental noise and thermal environment were selected as evaluation indexes to construct the air quality monitoring and evaluation index system during the construction period of the CTM mountainous highway tunnel.Meanwhile,adopting AHP(Analytic Hierarchy Process)combined with extension theory(extenics),the AHP extenics comprehensive evaluation model of air environment during tunnel construction period is established,and the advantages of simple dependent function and AHP are fully utilized to overcome the subjective and objective errors,and further improve the method of monitoring and evaluation of tunnel construction environment in China.The drilling,exiting,shotcrete and secondary lining of the CTM mountainous highway tunnel are selected as the starting point for the environmental assessment.And the model is applied to actual construction of the CTM mountainous highway tunnel.The results could objectively reflect the real situation of the environment of each construction operation in the cave of the tunnel.(2)By summarizing fluid mechanics and fluid mechanics theories,it can be seen that the airflow field in the tunnel ventilation process has certain complexity and the CO concentration distribution has certain uncertainty.The FLUENT software is used to establish a numerical analysis physical model for the actual construction ventilation of the CTM mountainous highway tunnel.The form and characteristics of the numerical simulation turbulence model of the ventilation are analyzed,and the re-normalization equation model adapted to this paper is obtained,which greatly improves the accuracy of solving eddy current problem.(3)Through the analysis of the airflow field of the CTM mountainous highway tunnel,the author notices when the distance between the tunnel face and the ventilation pipe is 30m,it is an effective range.In the range of the press-in type tunnel ventilation airflow from the outlet of the air duct to the tunnel face of,there is a characteristic of a limited space-attached wall jet such as an adherent jet and a restricted backflow.For the vortex center at about 7.5m in front of the tunnel face,the jet area is smaller than the backflow area.When the distance is 125m from the tunnel face,the airflow speed is basically stable.The velocity profile at different positions on the center plane and the profile of the airflow velocity at different heights of the same height are analyzed.The airflow field structure of the cross section of the CTM mountainous highway tunnel is divided into three areas:the eddy current zone,the eddy-affected zone and the stable zone.And the approximate distribution range of each area is within 35m from the tunnel face,35m to 125m,and 125m to 210m.(4)By studying the regularities of distribution of CO concentration in the CTM mountainous highway tunnel,the author notices when the airflow is about to reach the tunnel face,it is affected by the jet zone and the eddy current zone,and the concentration of carbon monoxide drops rapidly,at the same time,the carbon monoxide air mass flows toward the tunnel portal.Within 300 seconds before the ventilation,due to the influence of the eddy current zone,the concentration shows two peaks and stagnates.When the ventilation is about 23 minutes,the maximum concentration of carbon monoxide appears near the portal,and the concentration peak has been discharged outside the portal.When the ventilation is about 35 minutes,the maximum molar volume fraction of CO in the CTM mountainous highway tunnel is 1.6 x 10~-55 and the allowable concentration value of harmful gases in the cave has been met.By comparing and analyzing the concentration distribution map of CO at the center line at different times,it can be known that the carbon monoxide concentration curve continuously shifts to the right as a whole,and the CO concentration peak at each moment gradually decreases.,and the span between the peaks of CO concentration increases.In the process of moving the CO from the tunnel face to the portal of the CTM mountainous highway tunnel,the phenomenon of“migration”and“diffusion”overlaps.Lastly,the simulation results and the monitoring data are compared and analyzed.The general trends of the two types of data are basically consistent,which shows that the accuracy of the simulation and the established physical model of the CTM mountainous highway tunnel has high authenticity.This paper provides a reference for the improvement of the air environment system in the similar construction of mountainous highway tunnel. |
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