Study On Temperature Field Theory And Thermal Insulation Technology Of High Speed Railway Tunnel In Cold Region

With the rise of "the Belt and Road" initiative,there are more and more high-speed railway tunnels in cold region,frost damage of tunnel in cold region is becoming more and more pervasive.At present,the cold-proof design of tunnel in cold region is mainly based on experience,and no clear criteria for the classification of tunnel in cold region have been formed,the law of temperature field of tunnel in cold region needs further study,the influence of high speed train wind on frost damage of tunnel in cold region is still unknown.Therefore,to carry out the "study on temperature field theory and thermal insulation technology of high speed railway tunnel in cold region",by means of frost damage investigation of tunnel in cold region,field measurement,theoretical analysis and indoor model test,the main research results are as follows:(1)By surveying 156 tunnels subject to frost damage,we found the tunnels in cold region can be preliminarily classified into two groups:the tunnel at high latitude as well as the tunnel at high altitude.According to both of the average temperature in the coldest month and the frozen depth,tunnels were further subdivided into 5 sub-regions.On the basis of investigation data of frost damage,the relationship between the average temperature of the coldest month and the fortified length in different sub-regions was obtained,and the calculation method of the thickness of the insulating layer was deduced by using the equivalent thickness conversion algorithm.The cold-proof of long tunnel in cold region should not be confined to the entrance of tunnel,if the environment temperature is low,the initial ground temperature of surrounding rock is low,the train runs at a great speed or the number of trains is increasing per day,the long tunnel needs full tunnel cold proof.The method of thermal insulation layer is well applicable to the region where the average temperature in the coldest month ranges from-5 ? to-15 ?.For region with average temperature in the coldest month below-15 ?,other active insulation measures should be employed at the section where temperature exposes below-15 ?.(2)The temperature field model test system for high speed railway tunnel in cold region is developed,which is typically comprised of five components,i.e.,driving device of high speed train model,cold air temperature control device,regulation system of surrounding rock temperature(ground temperature),measurement system of wind speed and temperature,and tunnel model.Based on the temperature field model test system for high speed railway tunnel in cold region,the aim of this study is to carry out temperature field model test of high speed railway tunnel in cold region influenced by such varying variables as testing time,temperature outside tunnel,rock temperature,train running speed as well as train running intervals.Inspection of the testing results indicates that,deceasing 5 ? of outside tunnel air may increase 104 m of the minus temperature length from the portal;yet the minus temperature length for the portal reduces by 145 m,provided that the rock temperature increases by 5 ?,regardless of the influence of the natural wind.For the tunnel associated with train running interval less than 15 mins,the temperature variation and the minus temperature length increase obviously.Therefore,high speed railway tunnel in cold region has to take into account train running interval on the thermal insulation length.(3)The calculation models of temperature field for tunnel in cold region under the influence of the train piston wind are established by using the superposition principle,the method of separation of variables and Bessel's characteristic function,and the analytic solutions of air temperature field for tunnel in cold region under the influence of train piston wind are obtained,which provides the basis for setting up the air temperature boundary condition in the latter numerical calculation.Using the software Fluent to set up a fluid and solid coupled transient heat conduction model,variation law of air temperature field of tunnel in cold region is analyzed under different natural wind,ambient temperature and ground temperature of surrounding rock,the calculation results are compared with the temperature field test data of high speed railway tunnel in cold region.Keeping other conditions unchanged,each increase of natural wind speed of 1 m/s,the air temperature at the same position dropped by an average of 1.4 degrees Celsius,the air temperature curve of tunnel entrance to exit direction offset of 133 m,the air temperature curve of the tunnel exit to the inlet direction offset of 48 m;Keeping other conditions unchanged,each decrease of the outside temperature of 5 degrees Celsius,the air temperature at the same position dropped by an average of 1.68 degrees Celsius,each increase of surrounding rock temperature of 5 degrees Celsius,the air temperature at the same position increased by an average of 2.9 degrees Celsius.(4)A three-dimensional temperature field analysis model is established by Ansys,by comparing the temperature distribution law of tunnel with different length to determine the appropriate model length,by comparing the temperature distribution law of tunnel in different days to determine the appropriate simulation time,finally it is based on 3 000 meters long tunnel and 40 days' simulation time.The temperature distribution law of surrounding rock with and without thermal insulation layer under different temperature and different ground temperature is studied.The applicable range and thermal insulation effect of thermal insulation layer are analyzed and evaluated.(5)A new energy-saving air curtain insulation system for high speed railway tunnel in cold region is put forward,the system can automatically adjust the air curtain work according to the external environment,effectively reduce the amount of cold air entering into the tunnel and increase the temperature of the air in the tunnel,and does not affect the normal traffic safety.It is proved that 50 m air curtain in combination with 1 050 m insulation layer can meet the thermal insulation requirement of tunnel in cold region under extreme conditions,e.g.,ambient temperature of-30 ?,the ground temperature of surrounding rock of 5 ?,train speed of 300 km/h,and train operation interval of 10 minutes.(6)In order to study force variation law and failure mode of lining structure of tunnel in cold region,when the ponding position behind the lining structure is different,the indoor model tests of frost-heaving force are carried out.In order to analyze tunnel lining structure safety under the influence of frost-heaving force,the safety analysis software of tunnel lining structure in cold region is developed,which is used to analyze the safety of lining structure based on limit state method,the reliability of lining structure and the effect of surrounding rock grouting.(7)According to the investigation data of frost damage,taking the temperature conditions,hydrologic conditions,surrounding rock conditions and engineering measures,these four basic affecting factors as the criterion layer,the two level fuzzy comprehensive evaluation model is established by using fuzzy comprehensive evaluation method,and the weight of each factor is calculated by using the analytic hierarchy process,so as to establish the evaluation system of frost damage of tunnel in cold region.