Research On Safety Evacuation Technology Of Fire In Yangbajing High-altitude Highway Tunnel

With the in-depth implementation of the western development strategy in China,the construction of western expressways is changing rapidly.As an important part of the expressways,the number of high-altitude highway tunnels is increasing.Studying the safety evacuation technology of operating tunnels under fire conditions is of great significance for ensuring the safe escape of people in the tunnels.High-altitude areas have the characteristics of "low temperature,low air pressure,and low oxygen content" which greatly impact the movement capacity of people and law of tunnel fire development.Based on the Yangbajing tunnel with an altitude of 4250 m in Tibet,this dissertation focuses on the safe evacuation technology of fire mode personnel in high-altitude highway tunnels through data investigation,numerical calculation and field test.The main research conclusions are as follows:(1)By comparing and analyzing the combustion test in a plain area(Jiuli Campus of Southwest Jiaotong University)and the Yangbajing tunnel,the combustion time in the high-altitude area is 186 s longer and the heat release rate is 143% lower when the same substance is burned.A high-altitude tunnel fire model was established using FDS software,and the development law of combustion characteristics such as fire smoke concentration,smoke diffusion rate and temperature in the high-altitude tunnel was explored.(2)The criteria for determining the available safety evacuation time in tunnel fires was clarified.The FDS software was used to analyze different fire conditions in the Yangbajing tunnel,and the available safety evacuation times under different fire scales were obtained.A ventilation scheme of 0.5 m/s convection flow is given for all fire scales during the evacuation phase.(3)Field tests of the evacuation speed in the Yangbajing tunnel were conducted,and the evacuation speeds for people in different genders and ages in smoke and smoke-free conditions were obtained.The software Pathfinder was used to analyze the time required for safe evacuation of personnel in different design years.A comparative analysis of the available and required safety evacuation time under different fire scales shows that people can be safely evacuated under the fire scales of10 MW and 20 MW.Under the fire scale of 30 MW,it is recommended to change the spacing of cross passages to 170 m.(4)The critical wind speeds for different fire scales in the Yangbajing tunnel during the smoke exhaust phase are clarified.The influence of high-altitude environmental factors on the efficiency of tunnel fans was analyzed,and the control modes of the fans corresponding to the critical wind speeds under different fire scales were obtained.