Study On Fire Smoke Control Scheme Of "日" Urban Traffic Link Tunnel

With the consistent progress of cities,the public’s requirement of traffic is getting higher and higher,and the imbalance between provision and requirement occupies more and more important position.To solve this problem,underground roads were built.In recent years,the development of Underground Transportation Link Tunnels（UTLT）has been rapid,and many cities have begun to build underground tunnels according to their geological characteristics.UTLT structures are complex and mainly take the form of ring-shaped,channel-shaped,and composite-shaped tunnels,with small sections,high traffic volume,many entrances,exits,and branch junctions,steep slope gradients,and difficulties in smoke control,which poses a higher fire hazard.Therefore,it is urgent to strengthen research on smoke control in UTLT to reduce the harm and loss caused by fires.Compared with conventional UTLTs,the structure of"日"type UTLT is more novel,involving more risk factors,the internal flue gas movement law is more complex,and the losses caused by fire are also greater.Based on a tunnel project,this paper studies the flue gas control effect of the"日"type UTLT main tunnel and the connecting tunnel under different ventilation modes and the optimal longitudinal wind speed of the branch tunnel,and obtains reasonable smoke control measures and suggestions.The main research contents and research results are as follows:（1）Through data collection and theoretical analysis methods,the model parameters of the"日"type UTLT are determined,including grid,monitoring points,and simulation time.The tunnel fire scene is designed,the fire source layout and smoke prevention zone division are clarified,and the fire source location,fire source parameters and smoke prevention zone are set.The fire smoke control methods and indicators for the main tunnel,connecting tunnel and branch tunnel are clarified.（2）Through numerical simulation method,the smoke spread law of the main tunnel and the connecting tunnel under three ventilation modes:natural smoke exhaust,semi～lateral ventilation and full lateral ventilation is studied.Analyzing the fire parameters under different working conditions,it is found that the fire parameters in the two tunnels deviate greatly from the safety range during natural smoke exhaust.During semi lateral ventilation,the parameters of the downstream area of the main tunnel fire source are significantly better than the upstream area of the fire source.Only when the smoke exhaust speed in the upstream area of the fire source is 12.25m/s,all parameters meet the requirements of smoke control indicators.The fire indicators in the right half of the connecting tunnel are better than the left half,and only one indicator slightly does not meet the requirements when the smoke exhaust speed is 12.25m/s.During full lateral ventilation,the fire smoke spread range in the main tunnel is small.Only when the smoke exhaust speed is 6.25m/s,it is more suitable to meet the smoke control index requirements,and the smoke exhaust speed should be set around 6.25m/s.The degree of optimization of various fire parameters in the connecting tunnel is large.When the smoke exhaust speeds are 8.25m/s,10.25m/s,and 12.25m/s,all fire parameters meet the requirements of smoke control indicators,and 8.25m/s can be chosen as the optimal smoke exhaust speed.（3）Under the same smoke exhaust speed of the main tunnel,compared with the semi-lateral ventilation smoke exhaust method,the full transverse ventilation smoke exhaust method can control the fire smoke in a smaller range.But with the increase of the smoke exhaust speed,the changes of various fire parameters in the local area of the tunnel are intensified,the fluctuation is large,and the relevant indicators in the local area exceed the smoke control requirements.When the connecting tunnel adopts semi-transverse and full transverse ventilation,at the same smoke exhaust speed,the full transverse ventilation smoke exhaust method has a better smoke exhaust effect under the same smoke exhaust speed.（4）For the branch tunnel,the smoke spread law under the conditions of natural smoke exhaust and longitudinal ventilation was explored.It is found that when the branch tunnel is connected to the main tunnel,the optimal longitudinal wind speed of the three types of branch tunnels(v_直1=2.26m/s、v_弧1=2.46m/s、v_直角1=3.42m/s)is quite different from the theoretical critical wind speed(v_直=2.73 m/s、v_弧=3.04 m/s、v_直角=2.48 m/s).When the branch tunnel is separated from the main tunnel,the optimal longitudinal wind speed of the three types of branch tunnels(v_直2=2.13m/s、v_弧2=2.43m/s、v_直角2=3.16m/s)decreases to varying degrees,indicating that the main tunnel has a certain hindering effect on the ventilation and smoke exhaust of the branch tunnel.This effect should be taken into account when designing the smoke exhaust,and the design ventilation speed of the branch tunnel should be appropriately increased according to the tunnel type.