| It is known in the field of railway tunnel ventilation that,in addition to the natural winds from the entrance or exit of a tunnel,mechanical ventilation and train-induced winds are present inside the tunnel and cannot be ignored when the tunnel is in use.It is not clear that how the train-induced winds and mechanical ventilation influence the temperature field of cold region railway tunnels.Thus,this dissertation primarily examined the lnfluence of natural,mechanical ventilation and train-induced winds on the temperature fields in cold-region tunnels based on both theoretical finite difference calculations,the results of field investigations and the result of model experiment.In addition,the effects of mechanical ventilation and train-induced winds on the freezing scale in a cold-region tunnel were analyzed.Taking the Nan Shan railway tunnel in cold region as an example,othogonal test method respectively taking different indexs was applied to conduct sensitivity study of the influencing factors of tunnel temperature field.The regular functions of longitudinal frozen lengths about different cold regions weather were fitted using the calculation results of unsteady-state finite-difference calculation model.At the long time tunnel operation stage,the circular section model can be used to calculate the temperature field instead of actual horseshoe cross section,verified by the temperature field analysis of horseshoe shape tunnel and corresponding equivalent diameter circular tunnel under the same conditions calculated by CFD software.Finite difference temperature calculation software TTCS was established based on convection and heat conduction coupling model,and temperature field of airflow,lining and surrounding rock were entirely calculated using TTCS in cold region railway tunnel.According to the similarity theory,to conduct the similar model test and to study the heat transfer and distribution law of the cold region tunnel’s temperature field,the I:30 test platform for cold region tunnel’s temperature field were firstly designed and set up.The temperature changes dramatically when getting close to the lining of the tunnel,and becomes to 0℃ when the distance comes to 40 cm from the lining.The airflow temperature drops quickly at the beginning of the test and it becomes close to the entrance airflow temperature when time goes.The temperature of the airflow and surrounding rock changes as the law of entrance airflow temperature with a time-lag effect.The calculation results of TTCS matches the test results of 1:30 test platform greatly,proving the validity of the convection and heat conduction coupling finite difference calculation software TTCS.The in situ temperature field of a cold region railway tunnel has a good agreement with the calculated results by TTCS.It shows that the temperature of the tunnel lining and surrounding rocks has the same change law with the periodic changing entrance air temperature.The finite-difference model proposed in this dissertation can be used to guide the design of insulation layers for cold-region railway tunnels,thereby overcoming the difficulties encountered because of the complexity of modeling and stringent hardware requirements of general finite element software in temperature calculation of super long tunnel.The temperature of entrance airflow and speed of the airflow in tunnel affects the temperature field greatly.In the calculation model of this dissertation,the temperature of the second lining rises about 7.2 ℃ when the temperature of the entrance airflow rises every 10℃ from-20℃ to 20 ℃.The temperature of the second lining drops about 6.6℃,2.7℃,1.5℃ and 0.9℃ when the speed of the airflow rises every 1 m/s from 1 m/s to 5m/s.There are many factors affecting the temperature field of tunnels in cold region.Using TTCS,taking the Nan Shan railway tunnel in cold region as an example,othogonal test method respectively taking the internal nodes average temperature of tunnel lining,the temperature of lining of a certain section and longitudinal frozen length of tunnel entrance as indexs was applied to conduct sensitivity study of the influencing factors of tunnel temperature field.The results show that there are some local differences in the ranging of sensitivity of each factors under different indexs.Overall,depth of tunnel,wind direction in tunnel,tunnel section size,the wind speed in tunnel,wind temperature of entrance,thermal conductivity coefficient of surrounding rock are the main factors affecting the temperature field of tunnel,the surrounding rock density and the specific heat of the surrounding rock are the secondary factors affecting tunnel temperature field.In the antifreezing design of the tunnel in cold region,removing the factors which can not be changed like the surrounding rock density,the surrounding rock specific heat,the surrounding rock heat transfer coefficient,thermal conductivity of surrounding rock,wind temperature of tunnel entrance,sufficient attention must be paid on the design parameters which affect the temperature field of tunnel greatly like the depth of tunnel,wind direction in tunnel,the wind speed in tunnel and tunnel section size.The insulation layer is suggested to construct outside the second lining according to the more effective heat preservation and convenience to service and replace than constructing insulation layer between the first lining and the second lining.The higher train speed and larger train amount will increase the frozen length of cold region railway tunnel,but are not remarkable as natunal wind in tunnel.The directions of train-induced wind affect the frozen length greatly,which will increase the frozen length when along with the natural wind and will decrease it when on the contrary with the natural wind.The freezing injury forming mechanism,antifreeze and frost resistance of shallow buried tunnel in high latitude cold region were discussed.The observations shows that the shallow buried tunnel in high latitude region can not keep out of reezing injury using traditional heat preservation measures.The waterproof and drainage measures are the main antifreezing methods of shallow buried tunnel in high latitude cold region.Full-length deep center ditches,sub-drains and side insulation ditches are adviced to be used,with the diameter of above 80cm of the deep center ditches.Taking the length,section area,cover depth and the airflow temperature into account,the temprature of southwest high altitude region tunnels and northeast high latitude region tunnels was calculated using TTCS.It is found that,cover depth affects the frozen length of cold region tunnel significantly,while the tunnel length affects the frozen length non-significantly.The frozen length increases with the larger section area under the same cover depth.Under the cover depths from of 300m to 800m,the frozen length decreases with the larger cover depth until reaches the minimum frozen length.Finally,the frozen length formulae of southwest high altitude and northeast high latitude tunnels were fitted.The frozen length formulae were verified by the in situ investigation data of the Nan Shan tunnel,Sui Fenhe 1#tunnel and Sui Fenhe 2#tunnel.The operation temperature field of Nan Shan tunnel in northeast china was calculated using TTCS,taking mechanical ventilation and train-induced ventilation into account,the frozen length was verified by comparing the calculated results with the data from the in situ investigation of the Nan Shan tunnel. |
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