Research Of Thermal Environment And Ventilation System Of Underground Single-hole Double-line Tunnel Of Municipal Railway

With the increasing level of urbanization in China,the construction of Municipal Railway,as a means of transportation connecting central cities and surrounding cities,is accelerating.As the urban land becomes increasingly tense and the use space is limited,the Municipal Railway is also gradually developing to the underground space,especially in the urban section,the number of underground stations and underground tunnels has increased significantly.At present,the domestic underground railway tunnel usually adopts the single-hole and single-line mode,that is,the trains of two lines run in their own independent tunnel,while the underground tunnel adopts the single-hole and double-line mode,which can significantly reduce the civil engineering area and initial investment.But the problems of too large sectional area and crossing of two trains are adverse to the ventilation and the heat exchange,resulting in high air temperature in the tunnel.In order to meet the actual engineering needs of reducing the initial investment,shortening the construction period and adopting the single-hole and double-line tunnel mode in special areas,and meet the requirements of environmental control,it is very necessary to study in combination with the characteristics of urban railway and single-hole and double-line tunnel.Therefore,this thesis studies the single-hole and double-line tunnel mode of Municipal Railway from four aspects:ventilation and thermal environment characteristics and their influencing factors,the establishment of tunnel maximum air temperature prediction model and the design and comparison of actual line ventilation scheme,so as to provide reference for engineering design.Firstly,this thesis investigates the domestic municipal railway lines,and establishes the ventilation network model of single tunnel,single tunnel and double track tunnel of Municipal Railway through the investigation data,and compares and analyzes the difference between single tunnel and double track mode and single tunnel and single track mode from the perspective of ventilation and thermal environment through numerical simulation.The research shows that the intake and exhaust volume of the piston air shaft are reduced by 18.9%～36.4%and 29.4%～51.2%respectively due to the influence of two-way passing,large section of the tunnel and the setting mode of the piston air shaft;The air volume of section tunnel decreased by 57.9%～83.3%;The total ventilation rate decreased by 67.5%～51.5%.The air temperature distribution of single tunnel and double line tunnel shows the characteristics of low tunnel end and high middle station section.If the track arrangement system is not turned on,the station section is prone to high temperature,resulting in small heat exchange area and convective heat transfer coefficient.Secondly,the influence of 13 factors on tunnel air temperature and ventilation heat exchange is analyzed from five aspects:piston air shaft parameters,rail exhaust air volume,traffic organization,tunnel parameters and temperature parameters.The research shows that these parameters will have different degrees of influence on tunnel air temperature and ventilation heat exchange.Among them,increasing rail exhaust air volume,setting of intermediate air shaft and station middle partition wall are the most feasible optimization methods.At the same time,the parameter sensitivity analysis of the important index of the maximum air temperature of the tunnel is carried out.The sensitivity is sorted into outdoor air temperature,train number,train speed,train formation,rail exhaust air volume,section tunnel length,number of stations,soil temperature,blocking ratio,piston air shaft area and piston air shaft length.Thirdly,in order to predict the maximum air temperature of the tunnel and quickly determine the air volume of the environmental control track exhaust system,multiple factors are analyzed by multiple linear regression,and the prediction models of the maximum air temperature of the tunnel under the four modes of single tunnel double line,single tunnel double line+Intermediate air shaft,single tunnel double line+station middle partition wall,single tunnel double line+intermediate air shaft+station middle partition wall are obtained,Six of the influence parameters passed the significance test and were taken as the independent variable parameters of the model.According to the significance degree,they were sorted into outdoor air temperature,train number,train speed,train formation,rail exhaust air volume and section tunnel length,which were consistent with the conclusion of sensitivity analysis.Through the comparison between the models,the applicable conditions for the setting of intermediate air shaft and station middle partition wall were determined.Finally,based on a line in Chengdu,the maximum air temperature prediction model of the tunnel is applied to study the ventilation scheme in different operation periods.At the initial stage of operation,natural piston ventilation is adopted for the four modes.The rail exhaust air volume of a single station in the short term is 70/50/80/80 m~3/s,and the rail exhaust air volume of a single station in the long term is 90/80/120/120 m~3/s.The setting of intermediate air shaft in the near and long term of the line can enhance the air exchange and heat exchange of the tunnel and reduce the air volume of rail exhaust,while the setting of station middle partition wall will reduce the utilization efficiency of rail exhaust system and increase the air volume demand of rail exhaust.