Research On Jet Flow Gallery Ventilation Technology Of Toxic And Harmful Highway Tunnel During Construction

With the urban development, numbers of traffic and municipal tunnels show up in mountainous and hilly area. During tunnel construction, mechanical exhaust, blasting smoke, and toxic gases overflowing from stratum, if not be properly controlled, will accelerate in tunnel and endanger worker health and the construction safety. Therefore, in order to improve construction environment and protect the people in tunnel, effective measures of tunnel ventilation must be taken. Jet flow gallery ventilation is a common method for construction of double holes tunnel and single tunnel with parallel hole. It’s meaningful and practical to take in-depth study this technology. The3D jet flow gallery tunnel ventilation model (the left tunnel is the outlet ventilation tunnel; the right tunnel is the inlet; middle cross passage connect the two tunnels) for double holes tunnel is established according to Huayingshan tunnel, using CFD software-FLUENT. The numerical model is used to analyze local flow field in tunnel, and to study influential factors of distribution of toxic air, like gas and hydrogen sulfide. At last, the application of jet flow gallery ventilation in Huayingshan tunnel is introduced. The main conclusions are as follows:1) The model results basically match the air flowing pattern in real tunnel ventilation.2) The simulation of gas gushing from the tunnel face show that: When a certain amount of gas exists in outlet or inlet ventilation tunnel, the polluted air will not affect the air of other tunnel face. So, in practical, according to the location of pollution sources, the air supply of inlet or outlet ventilation tunnel face can be adjusted appropriately to save energy.3) When gas overflow from the inlet tunnel face, the polluted air will get through the cross passage and then be exhausted from outlet tunnel. So the larger amounts of gas emission, the greater centration of gas exist in cross passage. In real tunnel ventilation process, according to tunnel monitoring data, effective measures, such as increasing air supply or allocating jet fans, should be adopted to avoid gas accumulation in eddy zone which is located at the junction between tunnel and cross passage.4)The blower installed in inlet tunnel is used for delivering fresh air to each tunnel face, in order to keep fresh air from polluted gas spreading, after analyzing gas migration law in multiple construction conditions, a conclusion is put forward that30m away from cross passage is a proper fan installation distance which can basically keep air fresh, in front of blower suction outlet, avoiding secondary pollution.5) When hydrogen sulfide (H2S:heavy gas) overflow from inlet tunnel face, mixing with fresh air, the concentration of H2S near ground is higher than that close to tunnel vault. This shows opposite case when gas (CH4: lightweight gas) mix with air. So in actual ventilation process, jet fan and air duct should be placed reasonably basing on different toxic gases properties.6) Huayingshan tunnel construction ventilation monitoring data show that: the concentration of H2S and CO about15m away from tunnel face follow the feature above: increase rapidly, and decrease gradually over ventilation time. And the time for harmful gases to get peak and reduce to standard limit is basing on the amount of blasting smoke.