Study On Ventilation Technology Of Extra Long Railway Tunnel In Alpine Region

In recent years,the construction of railway transportation network in western China has gradually increased,and the railway tunnel construction inevitably develops towards the direction of high-altitude long tunnel.When carrying out tunnel construction in high-altitude areas,not only the construction period and project quality should be considered,but also the health and occupational safety of the construction personnel should be considered.Therefore,when the construction is carried out in the high altitude area with low hypoxia and low efficiency of construction machinery,the construction ventilation technology has become an urgent problem to be solved in the construction of extra-long tunnel in the high altitude area.Taking the Ganqing Tunnel project as the research background,this paper summed up the advantages and disadvantages of different ventilation modes,fan and duct acquisition,discussed the flow field,CO and dust concentration of different ventilation parameters,and compared and optimized with the existing ventilation scheme by using statistical analysis,numerical simulation,field testing and comparative verification methods.It aimed to provide the corresponding ventilation scheme optimization ideas for the relevant construction projects of the long railway tunnel.The main work and results are as follows:(1)Based on the investigation of ventilation in the construction of long tunnel in high altitude area,this paper summarized the matters needing attention in the selection of air ducts and fans,generalized the advantages and disadvantages of different ventilation modes in tunnel construction and the applicable conditions,and discussed the necessity of pressurized ventilation in Ganqing tunnel.Through theoretical calculation,combined with the corresponding calculation formula of each ventilation parameter,the air demand is modified and calculated,and the calculation method suitable for the long tunnel in the high-altitude and cold area was summarized.(2)Based on the geological and environmental characteristics of Ganqing tunnel,the ventilation principle and layout scheme of Ganqing tunnel construction were discussed.Pressing ventilation was adopted in the construction of the positive tunnel and auxiliary adit,the partition pressing ventilation was adopted in the construction of the positive tunnel in the working area of No.1 ～ 3 inclined shaft,and the single head pressing and three-way method was adopted in the construction of the positive tunnel in the working area of No.4 inclined shaft.The paper introduced the monitoring scheme of dust,wind speed and CO concentration during ballast discharging construction,and analyzed the change law of CO concentration with distance and dust concentration with time.(3)The numerical simulation method was adopted to analyze the flow field distribution and relative pressure changes under different key ventilation parameters with No.2 inclined shaft air bin and No.3 inclined shaft air duct as the research object.The results show that the ventilation effect is significantly improved when the length of No.2 inclined shaft air bin is30 m,the middle partition is 6m and the fan is located in the middle of the outlet.The bending angle of the air duct of No.3 inclined shaft is 146°,and the bending radius of air duct is 6m.When the outlet of the air duct is 30 away from the face of the palm,the flow field distribution is more uniform and the ventilation efficiency is the highest.(4)By comparing and analyzing the wind speed,dust and CO concentration distribution of numerical simulation and field monitoring data,it is found that the numerical simulation results and field monitoring data have roughly the same variation law,but the numerical simulation optimization scheme has higher ventilation efficiency and can reduce dust and CO concentration below the allowable value faster,indicating that the optimization of ventilation parameters in this paper is correct,reasonable and reliable.Therefore,it is suggested to adjust the distance of air duct outlet from 40 m to 30 m at the construction site,so as to increase the air flow in the tunnel,reduce the concentration of dust and CO,and help to accelerate the construction progress.Through the above optimization research on the construction ventilation of Gansu-Qinghai tunnel,it is expected to provide a theoretical reference for the construction ventilation calculation analysis and optimization of extra-long tunnels in similar alpine regions.