| In recent years,since the economy is developed rapidly in coastal areas and the construction technology of undersea tunnels is gradually mature in China,the number of undersea road tunnels has been increasing.And as an urban tunnel,in order to achieve multi-level traffic diversion,urban undersea traffic link tunnels emerged.Urban tunnels have the characteristics of rapid renewal of traffic vehicles,a surge in traffic volume,increase of new energy vehicles,and a large volume of traffic that are easily blocked.Undersea tunnels have the characteristics of high relative humidity,rich salt mist and high accumulation of acidic gas concentration.Urban undersea traffic link tunnels have the characteristics of multi-tunnel and multi-point access.This thesis relies on the ventilation system design of Xiamen Xiang’an undersea tunnel,Xiamen Haicang undersea tunnel,BHW undersea tunnel and Lu’ao urban traffic link tunnel.It adopts various methods such as literature tracking,theoretical analysis,field testing,physical model test,numerical simulation and case empirical evidence,etc.The following four tunnel ventilation difficulties were caused by three ventilation features of urban undersea traffic link tunnels.（1）The characteristics of the ventilation environment in V-shaped slope urban undersea road tunnels are not clear.（2）The tunnel ventilation system is too large or insufficient due to large changes in traffic factors.（3）Influence of high humidity and salt-rich mist environment on ventilation effect in urban undersea road tunnel.（4）The bifurcation structure causes the superposition or dilution of pollutants in each ventilation section of the traffic link tunnels.The following conclusions may be drawn:（1）The influence of V-shaped slopes on environmental parameters and vehicle pollutants in undersea tunnel was clarified.The CO,NO2 and PM emissions of the uphill section are 2.78,1.28 times and 1.88 times that of the downhill section,respectively.The air demand for diluted NO2 in urban tunnels gradually becomes the control air demand.Due to high humidity,dust will aggregate with water droplets into particles with greater gravity,and the traffic wind speed on uphill section is low,causing the PM concentration on uphill section is significantly more serious than that on downhill section.A corrosive ventilated environment with high humidity,rich salt spray and high acidic gas concentration is formed in urban undersea road tunnels.（2）We obtained the value source and formulation principle of air demand calculation parameters for road tunnels in China,and explored the quantitative increase and decrease law of the benchmark emission factor,time factor updates and traffic parameter changes to the air demand.Then we propose a refined calculation method for the air demand of urban tunnels that takes into account the rapid renewal of traffic vehicles,large changes in traffic parameters,diluted NO2 and non-emission particles,etc.And it is applied to ventilation system design of BHW ultra-long undersea tunnel.In the design,the air demand was reduced by 53.1%and24.3%respectively compared with the 2014 China Guidelines and 2017 Shanghai Code.（3）It was measured that the average lift produced by jet fan in Xiang’an undersea tunnel was attenuated by 12.4%after seven years of operation.The dynamic attenuation mechanism of lift pressure caused by jet fans corrosion in urban undersea tunnels was revealed.Under salt spray corrosion conditions,the effect of accumulation and sedimentation,erosion and corrosion will increase the surface roughness of the jet fan blades and flow-through components,thereby decreasing airflow lift through the blades and deteriorates the internal environment.Based on surface roughness,corrosion depth and corrosion time,the calculation method of jet fan lift was established.A method of jet fans configuration considering fan corrosion in Xiamen road tunnels is proposed.（4）The design process of ventilation system adopting ramp semi-horizontal+main tunnel longitudinal combined and the coupling method between two ventilation systems are clarified.A theoretical calculation model of the actual ventilation volume of each ventilation section considering the flow of pollutants in urban traffic link tunnels is established:the ventilation volume should be calculated in the opposite direction according to the airflow direction,and the actual ventilation volume of each ventilation section meets:the actual ventilation volume of the i segmentVi≥(the sum of the required air volume of all ventilation segments after the i segment （?）+air demand of i segment.The effects of ratio of length and height of the enlarged section of bifurcation structure,split ratio and bifurcation angle on the ventilation force are revealed.The results provide theoretical support and basic design basis for air volume,wind pressure calculation and operation management in the ventilation system design of urban tunnels,undersea tunnels and traffic link tunnels. |
