Research On Construction Ventilation And Oxygen Supply Technology For Long-distance Construction Inside The High Altitude High Ground Temperature And Extra-long Tunnel

The planned Sichuan-Tibet railway is located in Sichuan Province and Tibet Autonomous Regionin China,starting from Chengdu City,Sichuan Province,and ending in Lhasa City,Tibet.The construction of Chengdu-Ya’an and Lhasa-Linzhi sections has started.The Ya’an-Linzhi section is still in the stage of engineering feasibility study due to the complexity of geographical environment,design and construction technology,and the difficulty of disaster prevention and control.In thisarticle,the technology ofthe construction ventilation and oxygen supply for the Sichuan-Tibet Railway highaltitude,high ground temperature and extra-long tunnel construction,the main studying contents and findingsinclude:(1)Ventilation technology for high ground temperature tunnel construction,study the influence of factors such as ventilation speed,ventilation temperature,initial temperature of surrounding rocks,and construction cycle footage on tunnel temperature.The temperature distribution of tunnel and surrounding rock under different working conditions is analyzed.The results show: with different ventilation speed,after 120 min ventilation,the average air temperature in the tunnel shows that the ventilation speed has little effect on the air temperature in the tunnel;the wall temperature shows that the higher the ventilation speed is,the lower the wall temperature is.The results show that the lower the ventilation temperature is,the lower the air temperature and the wall temperature are,and the lower the low temperature range is.The relationship between the average air temperature and the ventilation temperature is linear,and the relationship is deduced.When the initial temperature of surrounding rock is different,after ventilation for 120 minutes,the average temperature value and wall temperature value in the tunnel indicate that the lower the initial temperature of surrounding rock,the easier to cool down,and the lower the temperature in the tunnel after ventilation.When the cyclic footage of tunnel construction is different,after ventilation for 180 minutes,the average air temperature and wall temperature values in the tunnel indicate that the distance from the vent pipe outlet to the tunnel face should be within a certain range,and the long distance from the vent pipe outlet to the tunnel face is not conducive to the cooling of the construction area after the tunnel face.(2)According to the relationship between altitude and atmospheric pressure,the oxygen supply quantity is calculated by theoretical formula;the oxygen supply method and oxygen concentration distribution near the tunnel face are simulated by FLUENT software,the conclusion is as follows:it is more feasible and effective to improve the oxygen concentration near the face than to use the ventilation method.When the oxygen concentration in the range of 5 m behind the face reaches the standard value,the diffusion type oxygen supply is adopted and the oxygen supply is the least under the condition of no ventilation.The research results can provide reference for the construction ventilation and oxygen supply schemes for the construction of highaltitude and high ground temperature tunnels on the Sichuan-Tibet Railway.