Study Of Combusyion Characteristics And Smoke Flow Control Method Of Highway Tunnel In Very High Alititude Area

The typical "Three-step" terrain,the implementation of China's western development policy and the improvement of Chinese road network have caused a large number of completed and planned road tunnel construction work in high altitude areas.Some of them are at altitudes even higher than 3,500 m.The tunnel fire safety,in such context,is particularly important at the very high altitude areas.The unique environmental characteristics of low atmospheric pressure and low air density in very high altitude areas will lead to significant changes in the basic combustion characteristics and smoke flow control of highway tunnel fires.Therefore,it is clear that the basic tunnel fire combustion characteristics and the tunnel fire safety control mechanism are the most important parts to solve the tunnel fire safety problem at very high altitude areas.In order to solve the problems faced by highway tunnel fires in very-high altitude areas and reveal the effect of high altitude on the basic combustion characteristics and smoke control in highway tunnels,a combination of research methods including fire model test in different altitude areas,theoretical analysis based on basic theories such as fire combustion and fire dynamics and numerical simulation has been adopted.The objects of the investigation are mainly focused on combustion characteristics,smoke flow control and smoke control in cross-passages at bi-directional road tunnel fire,etc.The main research work and achievements of this thesis are as follows:1.Basic combustion characteristics of tunnel fires in very high altitude areas was investigated by conducting a series of tunnel fire model tests at different altitudes.Firstly,the effect of high altitudes on burning rate,temperature distribution characteristics of fire source section and longitudinal temperature distribution characteristics of tunnel fire are revealed with the experimental results.Then the essential relationships between the burning rate and the altitude,the maximum ceiling gas temperature and altitudes are respectively identified through a combination of experiments and basic theoretical analysis based on fire combustion and fire dynamics.Finally,a mathematical calculation model of heat release rate(HRR)for tunnel fire scenarios,a theoretical model of the maximum temperature of the tunnel ceiling and a design calculation model of the maximum ceiling gas temperature are proposed for the first time.These models are suitable at vary altitudes.2.The essential relationship between the special low-atmosphere-pressure,low-density environment characteristics and the critical velocity of tunnel fires in very high altitude areas is clearly defined.The effect of high altitude and HRR on critical velocity of tunnel fires is revealed.The basic theoretical mathematical calculation model of highway tunnel fire critical velocity and the design ventilation model for fire and smoke control of highway tunnel fire are proposed for the first time.The above two models are suitable at different altitudes.3.The variation law of tunnel fire critical velocity in cross-passages at bi-directional road is proved.The basic theoretical mathematical calculation model of critical velocities for smoke control in tunnel cross-passages and the design ventilation model for fire and smoke control in tunnel cross-passages were proposed for the first time.The above two models are suitable at different altitudes.The research results of this paper can not only improve the theory of tunnel fire research in China's very high altitude areas,but also provide scientific basis and theoretical support for the perfection of specifications conducting tunnel fire ventilation system design of highway tunnels.In addition,some of the research results are also be useful for disaster prevention and evacuation design in very-high-altitude railway tunnel.