Study On Temperature Field And Anti-freezing System For Cold-region Tunnels With High Geotemperature

In recent years,China is in the period of high-speed development of railway construction,especially high-speed railway.Railway construction is gradually developing towards high altitude,complex geology and other areas.Taking Sichuan Tibet Railway as a representative,the cold area high temperature tunnel has become a unique tunnel project.For such tunnels,the phenomenon of high temperature heat damage and low temperature freezing damage coexists.In this paper,the temperature field change law of high temperature tunnel in cold area under long-term operation ventilation is studied by using the unsteady finite difference calculation model of tunnel surrounding rock lining wind flow,The change law of the length of the tunnel freezing under different natural ventilation and driving conditions is obtained.Based on this,a new anti-freezing system and calculation method are proposed for the tunnel with high temperature in the cold area.The freezing damage of the tunnel opening can be solved by using the high rock heat energy in the tunnel.The main conclusions are as follows:(1)Based on Zilashan tunnel of Sichuan Tibet railway,a three-dimensional unsteady heat transfer model of surrounding rock lining air flow is established.The dynamic change law of temperature field of high temperature tunnel in cold region under the action of natural wind and train piston wind is studied.The results show that the wind flow makes the overall temperature of surrounding rock drop and the lining temperature at the entrance end is lower than 0 ℃;The lining and surrounding rock at the exit end are heated by high temperature wind flow,and there is no frost damage;Different train operation modes make different train piston wind in tunnel,and piston wind which is the same direction as natural wind will increase the anti-freezing length at the entrance of tunnel,while reverse piston wind will reduce the length of tunnel anti freezing.(2)Taking Zilashan tunnel as an example,the variation law of freezing length of high temperature tunnel under the influence of natural ventilation is studied.The research shows that the length of freezing protection at the tunnel portal will vary with the natural wind speed,natural wind temperature,driving speed and driving density;When the train passes less than 20 pairs per day,the tunnel entrance end will suffer from frost damage.When the number of trains increases from 20 pairs to 30 pairs,the tunnel frost damage will be transferred from the entrance to the exit.The anti-freezing length increases with the increase of train density.(3)According to the distribution law of temperature field in the cold region high temperature tunnel,a new anti-freezing system and corresponding calculation method are proposed.The system includes heat collection system,control transmission system and heating system of heat exchanger.The preliminary design is based on Zilashan tunnel and the laying length of the insulation layer at the tunnel portal is 1300 m,the laying length of the insulation layer is 300 m,the maximum heating load in winter is36.83 k W,and the minimum heating load is 24.55 k W;The equivalent diameter of the section of the hot chamber is 5m,and the length of the hot chamber is set to 60 m.