Design Optimization Of Fire Smoke Control Under The Centralized Smoke Exhaust Mode In Extra-wide Section Immersed Tunnel

Compared with traditional tunnels,the extra-wide section(single-hole four-lane and above)immersed tunnels have special features such as special section shape and large aspect ratio.When a fire occurs,it will have a different fire occurrence and development process than the general tunnel.Little research at present.With the rapid development of underground space engineering in China,tunnels with special cross-sections have emerged in China.Studying the fire characteristics of extra-wide section tunnels and finding suitable anti-smoke technologies for the extra-wide section are the specific needs of China’s current social development.To this end,the theoretical analysis and numerical simulation methods are used to optimize the smoke extraction technology of the extra-wide section immersed tunnel.Mainly carried out the following aspects of research:(1)Study the influence of the parameters(area,spacing,number)of the exhaust outlet on the smoke exhausting effect in the top exhaust mode of the super wide section immersed tunnel.The 20 MW size fire source was selected,and the FDS numerical simulation study on the parameters of the exhaust vents showed that the area of the exhaust vents had no obvious influence on the smoke exhausting effect.Properly increasing the spacing and number of the venting ports is beneficial to the tunnel exhausts smoke.(2)Study the effect of one,two or three rows of exhaust vents on the lateral exhaust of extra-wide section immersed tunnels.The fire source of 20 MW is selected,and the FDS numerical simulation study is carried out on the exhaust vents with different rows at the top.It is found that the number of exhaust vents can be effectively controlled in the lateral direction of the tunnel while ensuring a certain amount of smoke.The spread of smoke and the height of the smoke layer in the tunnel can also improve the efficiency of the system.(3)Study the effect of longitudinal air volume on the smoke exhausting effect of the system when the smoke exhaust of the exhaust fan is fixed in the centralized smoke evacuation mode in the conventional underwater tunnel and the extra-wide section immersed tunnel.The fire source of a certain power is selected,and the FDS numerical simulation of the conventional tunnel fire and the extra-wide section immersed tunnel fire under different ventilation conditions is carried out.It is found that the larger the longitudinal wind speed,the shorter the smoke spread distance.When a fire occurs,evacuate and rescue the personnel,win more available safe evacuation time,and send a certain proportion of air supply to suppress the settlement of the smoke,provide a good evacuation environment for personnel escape and fire rescue;increase the air volume The proportion affects the total exhaust efficiency of the system.When the air volume is increased to 90% of the smoke exhaust,the spread distance of the flue gas can be better controlled,and the total exhaust efficiency of the system can be improved to some extent.Comprehensive consideration,the amount of replenishment should be designed to 90% of the concentrated smoke,which is more conducive to personnel escape.