Numerical Simulation Research Of Construction Ventilation In Drilling And Blasting Stage Of High Altitude Railway Tunnel

Sichuan-Tibet Railway passes through multiple geomorphic types,along the mountains and valleys,terrain conditions are extremely complex.The line direction presents “eight ups and eight downs”,involving a large numbers of typical high-altitude super-long railway tunnels.However,the plateau climate and geological characteristics bring severe challenges to the safety and reliability of tunnel construction ventilation.Drilling and blasting method are widely used in Sichuan-Tibet railway construction,and blasting will inevitably lead to air quality reduction.It is particularly important to improve or maintain the construction ventilation efficiency.In the actual tunnel construction ventilation process,the air demand at each altitude,the wind speed of the duct,the initial mass concentration of CO and the ambient temperature will affect the ventilation effect.It is of great significance to comprehensively consider the influence of environmental factors such as altitude on the ventilation of drilling and blasting construction.Generally,the field measured data are more reliable,but the measurement is too difficult.The wind tunnel test is also difficult to simulate the air density change caused by altitude,and then the numerical simulation method can better solve the above problems.Therefore,this article adopts numerical simulation method,aiming at the influence of altitude and ground temperature on airflow characteristics in tunnel,a three-dimensional model of double-track railway tunnel is established by CFD software,and the influence of multi-factor changes caused by altitude on airflow characteristics is studied.On this basis,the effect of ground temperature on airflow characteristics and pollutant diffusion rate is studied.The main research contents of this paper are as follows:(1)CFD numerical simulation is used to simulate the influence of multi-factor linkage on the migration law and dilution effect of harmful gas in the construction ventilation process of double-track railway tunnel drilling and blasting method.The results show that: affected by the linkage factors,the peak concentration of harmful gas at each monitoring point in the high-altitude tunnel decreases linearly with the ventilation time.The smoke safety distance obtained by fitting the numerical simulation results is much larger than the standard formula value.Smoke exhaust safety distance is an important parameter in the design of ventilation length.The ventilation length is too short,resulting in CO concentration exceeding the limit in other construction processes of the tunnel.(2)The influence of constant ground temperature and different altitudes on the size of the temperature comfort zone,and the influence of constant altitude and different ground temperatures on the size of the comfort zone are studied.The influence of altitude and ground temperature on the temperature field in the tunnel is obtained,and then the size of the comfort zone with different altitudes and different ground temperatures is obtained.The results show that under the influence of altitude and ground temperature,the ground temperature T and the distance X of the tunnel face show a cubic nonlinear relationship.(3)Coupling of altitude and ground temperature accelerates pollutant diffusion.