| With our country's steady economic growth,the transportation network is gradually perfect,the network of railway and highway road gradually extends to the altitude cold region,which is inaccessible to people and has harsh natural conditions,Most of these areas are known for their features such as high altitude,low temperature,and poor weather conditions.Construction of highways,railways,and other ground transportation infrastructure in these areas generally requires the construction of tunnel projects.The prevention about Freezing damage of the tunnel lining structure are the key technologies for solving the anti-freezing damage of tunnels in cold regions and determine whether the tunnel is safe during construction and operation.Based on the Dang Jin Shan Tunnel of Dunhuang-Geermu Railway which is under construction,this paper uses a combination of theoretical analysis and numerical simulation which Couples analysis of temperature field-stress field of tunnel in high altitude and cold area under group cave of tunnels in high-altitude cold regions under group cave conditions,and studies the effect of laying insulation layer on the distribution of temperature field,vertical displacement field and equivalent stress of lining structure of tunnel under the different conditions of caverns;t Through the analysis of the selection of insulation layer,the thickness and the length of the insulation fortification section in tunnel entrance section,it is proposed that tunnel insulation tunnel section along the tunnel Longitudinally lays different thickness insulation;points out that the installation of electric heating system in the tunnel entrance section under extreme temperature conditions to assist the cold protection measures of the tunnel,and the relationship between the power of the electric heating system and the air temperature inside the tunnel was studied;finally,the thermal insulation effect of the tunnel is forecasted from two aspects of the transient temperature field of surrounding rock under the condition of extreme air temperature and normal temperature.The conclusions are as follows:(1)The influence of changes in outside atmospheric temperature on the temperature in the cave is approximately 2000 m from the entrance.The temperature in the cavern exceeding 2000 m is positive,and the temperature in the tunnel entrance is approximately 0? for about 5 months per year.(2)Under the premise that the main tunnel,flat guide,and cold discharge tunnel are not covered with thermal insulation layers,the depth of the cavern expansion ring in each cavern gradually increases with the increase of loading time.When the horizontal distance between the main tunnel and the tunnel is 40 m,the horizontal The parallel tunnel will accelerate the frost heave of the main tunnel,but has no effect on the depth of the frost heaving circle of the main tunnel;when the three holes are present,the equivalent stress value at the wall of the cold discharge tunnel is the highest,at 10.73 MPa,which is the most dangerous part.In the construction and operation,the supporting rigidity of the side wall should be strengthened to ensure the safety of the tunnel;(3)The 5cm insulation layer of the main tunnel,para,and the cold discharge hole can reduce the scope of the heave expansion zone of the caverns to a greater extent.Five months after loading,there is a negative temperature zone in the insulation layer and secondary lining of the main tunnel.There is a negative temperature zone in the thermal insulation layer and the primary support of the parallel tunnel,and the negative temperature zone of the cold discharge hole exists only in the thermal insulation layer.There is no negative temperature zone in the surrounding rock of the lining structure of each cavern,and the range of frost heave of each cavern after the laying of the insulation layer in the main tunnel,parallel tunnel and the cold release tunnel shall not affect each other;(4)After comparing the performance of phenolic foam,polyurethane,polystyrene and high-pressure polyethylene and other thermal insulation materials,it is more suitable to use phenolic foam as the thermal insulation material of the tunnel;through analysis of laying 1cm,3cm,5cm,and 7cm insulation layers for the main tunnel,5cm,3cm,and 1cm insulation layers are laid for the cold discharge holes and parallel tunnel has no insulation showed that the thickness of the main tunnel and the cold discharge hole with different thicknesses had no effect on the depth of the frost heave.When the thickness of the insulation layer laid in each cavern increases from 1cm to 3cm,the depth of the frost expansion ring in each cavern can be reduced by up to 1m.(5)Through multiple numerical simulations and comprehensive analysis of empirical formulas,it is recommended that the length of the insulation section of the main tunnel be taken as 1350 m,a 1cm insulation layer should be set in the range of 955m?1350m from the tunnel entrance,and a 3cm insulation layer should be set in the range of 184m?955m from the entrance of the tunnel.5cm insulation layer is set in the range of 0?184m from the entrance of the hole;the insulation length of the cold discharge tunnel is 835m;3cm insulation layer is installed in the range of 835m?330m from the entrance;5cm insulation layer is set in the range of 0?330m from the entrance;(6)The temperature in the cave is lower than-15?.In addition to the insulation layer,the main tunnel and the opening of the cold discharge tunnel should be equipped with an electric heating system to assist the tunnel in cold weather.When the temperature in the cavity is between-15??-20?,the power of the electric heating system is 12W/m~2,the temperature in the cavity is between-20??-25?,the power of the electric heating system is 20W/m~2,the temperature in the cavity Between-25? ?-30?,the power of the electric heating system is 55W/m~2,the temperature in the cavity is between-30? ?-35?,and the power of the electric heating system is 130W/m~2.(7)In the extreme temperature conditions,if no electric heating system is installed,the temperature of the surrounding rock of the main tunnel and the cold-resistance hole near the discharge tunnel,the initial support of the main tunnel,the secondary lining and the lining structure of the cold discharge tunnel will be below-5?.if the electric heating system is installed,the temperature of the surrounding rock,the secondary lining,the lining structure of the cold discharge tunnel will rises to above-5?;the normal temperature condition is loaded for 5 years;the surrounding rock of the main tunnel and the cold discharge tunnel,the primary support of the main tunnel,the secondary lining and the cold-resistance hole near the discharge tunnel are above-5?.It shows that under the premise of not considering the aging of insulation layer,the comprehensive cold insulation measures proposed in the paper can effectively prevent frost heave damage in tunnels. |
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