Study On Smoke Exhaust Effect In Centralized Smoke Exhaust Mode Of Immersed Tunnel

In recent years,with the economic growth,China’s tunnel construction technology has developed rapidly,and immersed pipe method has quickly become the main method for underwater tunnel construction due to its advantages of low cost,high quality and short construction period.However,immersed tunnel is generally "V" shaped longitudinal slope,and the longitudinal slope is long,the tunnel space is narrow and closed,once a fire occurs,the smoke spread distance is longer,which is not conducive to personnel evacuation and fire rescue.Centralized smoke exhaust has good adaptability to the smoke exhaust needs of immersed tunnel due to its economy,effective control of pollutants,and uniform distribution of pollutants in the tunnel.Nowadays,the width of tunnels is increasing,and the choice of smoke extraction solutions for submerged tube tunnels with different widths and slopes is worth studying.In this thesis,a combination of theoretical analysis and numerical simulation is used to establish full-scale models of 10 m wide one-way two-lane,14.5 m wide one-way three-lane and 18.5 m wide one-way four-lane immersed tunnel,and the following studies are carried out on the centralized smoke exhaust of immersed tunnel.Firstly,the effects of tunnel width change on flue gas characteristics and smoke exhaust efficiency under the same smoke exhaust mode are studied,and it is found that with the increase of tunnel width,the flue gas spread rate decreases and the smoke exhaust efficiency also decreases.Subsequently,this paper analyzes the selection of smoke exhaust methods in immersed tunnel under different widths,and compares the smoke exhaust effects under the three smoke exhaust methods of side wall smoke exhaust,top smoke exhaust and side wall smoke exhaust plus smoke blocking vertical wall,and it is found that the top smoke exhaust is better than the other two smoke exhaust methods in terms of flue gas spread speed,temperature distribution,visibility distribution and smoke exhaust efficiency due to its superiority in structure,and the smoke exhaust effect is better than that of a single sidewall smoke exhaust method.Then,by analyzing the fire development of immersed tunnel under different ignition source powers,this paper finds that under the same tunnel width and smoke exhaust mode,the thickness of the flue gas layer and the smoke concentration in the tunnel will increase with the increase of the ignition source power,and the smoke exhaust efficiency will also increase.Since most immersed tunnels are "V" shaped longitudinal slopes,this paper analyzes the influence of flue gas characteristics and smoke exhaust efficiency and its mechanism of smoke exhaust efficiency in the slope section of immersed tunnel based on three tunnel slopes with tunnel slope i=0,1.5% and 3%,and the results show that under the action of chimney effect,when the tunnel slope increases,the flue gas in the tunnel will accumulate at the top of the slope,the smoke spread speed to the upstream of the fire source will accelerate,and the smoke exhaust efficiency in the tunnel will also decrease with the increase of slope,which will adversely affect fire rescue and personnel evacuation.Finally,the effect of three smoke exhaust methods on the chimney effect is studied by combining different longitudinal wind effects.It is found that the smoke exhaust effect of top smoke combined with longitudinal wind is better,and a reasonable longitudinal wind speed recommendation is put forward according to the smoke exhaust effect under different longitudinal wind speeds.