| Urban underground utility tunnel is an important infrastructure and ’ lifeline ’ that integrates various engineering pipelines such as power,communication,gas,heating,water supply and drainage,implements unified planning,design,construction and management,and guarantees urban operation.As of June 2022,China has started construction of 1647 underground utility tunnel projects in 279 cities and 104 counties,with a length of 5902 km and a corridor body of 3997 km.High-density cables are laid inside the underground utility tunnel.When the cables are short-circuited,overloaded,and arc-broken,a linear fire source will be formed.The fire spreads rapidly,releasing a large amount of toxic and harmful smoke,causing a large area of power outages in the city,which in turn causes serious economic losses.At present,the characteristics of linear fire plume are not clear,and the shape of fire source,the vertical position of fire source,the blocking rate and the length of fire compartment will affect the development trend of linear fire plume.The linear fire plume of utility tunnel under the coupling of multiple factors needs to be further studied.In this thesis,the influence of different fire compartments,sealing characteristics and vertical fire source location on the linear fire plume epidemic behavior in the utility tunnel is studied by combining experimental research and theoretical analysis.A linear fire source with a length of 1.9 m and a width of 4 cm was set up to build a fire experimental platform for the utility tunnel.By changing the symmetrical plugging rate at both ends of the utility tunnel,the vertical position of the fire source and the length of the fire compartment,the key characteristic parameters such as the maximum temperature rise of the ceiling smoke,the longitudinal temperature distribution of the ceiling smoke,the mass loss rate of the linear fire source and the heat release rate were obtained.The coupling influence of multiple factors on the linear fire plume characteristics in the utility tunnel and its interaction mechanism were revealed.The dimensionless maximum temperature rise prediction model under the ceiling of the utility tunnel under the coupling of different factors and the longitudinal temperature attenuation prediction model under the center line of the ceiling of the utility tunnel were established.The reliability of the model prediction is verified by relevant experimental results.The main research contents and results are as follows:(1)The coupling effects of different blocking rates and vertical fire source locations on the linear fire plume epidemic behavior in the utility tunnel were experimentally studied.Through analysis,the development process of linear pool fire can be divided into eight stages,and the flame height,shape and color of each stage are different.When the linear fire source is located at position 01(the closest to the ceiling)and position 03(the farthest from the ceiling),the blocking rate has no significant effect on the duration of the linear fire source.When the linear fire source is located at 02position(middle position),the duration of open fire will decrease with the increase of blocking rate.The maximum temperature of each measuring point of the pipe gallery always appears under the 100 % plugging condition;the mass loss rate of linear fire source will increase with the increase of plugging rate.The heat release rate of the linear fire source decreases first and then increases with the increase of the plugging rate.When the linear fire source is located at 01 position,the heat release rate is the smallest when the plugging rate is 50 %.When the linear fire source is located at 02 and 03,the heat release rate is the smallest when the plugging rate is 75 %.Through dimensional analysis,this thesis establishes a dimensionless maximum temperature rise prediction model of the utility tunnel ceiling under the coupling effect of the vertical position of the linear fire source and the plugging rate.The reliability of the prediction model is verified by comparing the experimental value with the predicted value.The prediction error is basically less than 5 %,within an acceptable range.Based on the theory of temperature longitudinal attenuation in long and narrow confined space,considering the vertical position and plugging rate of linear fire source,a prediction model of longitudinal smoke temperature attenuation under the central line of the roof of utility tunnel under the coupling effect of different vertical position and plugging rate of linear fire source is established.The prediction results are in good agreement with the experimental results,and the prediction error is basically less than 10 %,which is within an acceptable range.(2)The linear plume behavior of utility tunnel under the coupling of different blocking rates and fire compartment lengths was studied experimentally.When the blocking rate is 80 % and above,the flame of the linear fire source is in an extremely unstable state,and the jump and oscillation are very large.Under different fire compartment conditions,the open fire duration of the linear fire source will increase first and then decrease with the increase of the blocking rate.The duration of open fire is the largest at 20 % plugging rate.For the temperature measuring point directly above the linear fire source center,when the fire zone is 4 m and 6 m,the temperature curves under 80 % and 100 % sealing conditions will immediately decrease when the maximum temperature is reached,while under other sealing conditions,the temperature curves will have double peaks.The farther away from the roof of the utility tunnel,the smaller the difference between the two peaks.The temperature rise rate is always the fastest when 80 % and 100 % plugging,and the temperature drop rate is always the slowest under other plugging rates.Under different fire compartment conditions,there are two stable periods of mass change at each blocking rate,and the mass loss rate of the former is much smaller than that of the latter.The heat release rate of the linear fire source will decrease first and then increase with the increase of the plugging rate.The heat release rate of the linear fire source is always the smallest at 20 % plugging.When the fire compartment is 4 m and 6 m,the maximum temperature of the utility tunnel ceiling will increase first and then decrease with the increase of the plugging rate.When the fire zone is 8 m and 10 m,the maximum temperature will decrease first and then increase with the increase of the plugging rate,and then decrease after 80 % plugging.The maximum temperature of the ceiling is always the maximum when the fire zone is6 m.Through dimensional analysis,a prediction model for the maximum smoke temperature rise of the dimensionless ceiling of the utility tunnel under the coupling effect of the vertical position of the linear fire source and the plugging rate was established.The reliability of the prediction model was verified by comparing the experimental value with the predicted value.The prediction error is basically less than10 %,within an acceptable range.Based on the theory of temperature longitudinal attenuation in long and narrow confined space,considering the length of fire compartment and plugging rate,a prediction model of longitudinal smoke temperature attenuation under the central line of the roof of utility tunnel under the coupling effect of different fire compartment length and plugging rate is established.The prediction results of the model are in good agreement with the experimental results,and the prediction error is basically less than 10 %,which is within an acceptable range.The research results of this thesis can provide theoretical reference and guidance for the improvement of fire protection norms,fire risk assessment and fire protection design of utility tunnel. |
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