| With the development of economic construction in various countries and the promotion of development policies in the central and western regions of China and the "Belt and Road " initiative,the infrastructure construction of highways and railways in various countries has gradually extended to cold regions with extreme weather conditions such as high altitude and high latitude areas.The operation state of the tunnel shows that frost damage is widespread.In the past,the focus of tunnel construction in cold regions was on the evolution law of temperature field of tunnel surrounding rock,and less attention was paid to the influence of drainage tunnel on temperature field of surrounding rock in cold regions.In order to explore the relationship between the temperature field of tunnel surrounding rock and the discharge tunnel,this paper carried out field experiments to observe the evolution of the temperature field of the tunnel,deduced the hydrothermal coupling equation,simulated the temperature field under various working conditions in the presence of the discharge tunnel,and proposed the corresponding thermal insulation prevention and control scheme.The main research contents and conclusions of this paper are as follows :(1)Through the monitoring and analysis of the temperature field inside and outside the tunnel,this paper fits the atmospheric temperature outside the tunnel,providing boundary and initial conditions for the numerical simulation chapter.The temperature difference between the two ends of the tunnel,the left and right side walls and the longitudinal temperature distribution of the tunnel are explored.The average temperature of the Chorma tunnel is lower than that of the Nalati tunnel.In the closing stage of the cold door,the temperature of the left wall at the entrance of the Nalati cave is lower than that of the right wall,while the temperature distribution of the side wall at the entrance of the cave in the direction of the Cholma is opposite.In the opening stage of the cold door,the temperature of the right wall in the direction of the Cholma is higher than that of the left wall.The direction of the hole is opposite to that of Nalati;the longitudinal temperature of the tunnel is low and the middle temperature is high.In the cold door closing stage,the temperature distribution is more concentrated,and the cold door opening stage,the temperature is higher than the cold door closing stage,the temperature distribution is more dispersed.Through the analysis of the temperature at different locations,it is recommended to implement targeted thermal insulation and cold protection measures at different locations of the tunnel.(2)Based on the theory of porous media and basic assumptions,the hydrothermal coupling model of unsaturated frozen soil is derived and modeled by finite element software.The temperature field without the discharge tunnel,the temperature field of the transverse and longitudinal sections under different wind speeds,different water volumes and different flow rates in the tunnel are simulated.It is concluded that the existence of discharge tunnel will affect the temperature field of tunnel surrounding rock.The wind speed in the tunnel has the greatest influence on the temperature field of surrounding rock,followed by different water conditions,and the influence of different water flow velocity is small.The temperature field of surrounding rock reaches the most unfavorable condition under the condition that the wind speed of the tunnel is larger,the discharge tunnel is ventilated and the water flow velocity in the discharge tunnel is smaller.Therefore,through the analysis of the temperature field of surrounding rock,it is suggested that the thermal insulation layer should be laid on the slope of the tunnel outside the tunnel,and the wind and cold resistance measures should be carried out on the tunnel and the outlet of the tunnel.(3)In view of the most unfavorable situation and the existing Yuxi Molegai tunnel discharge tunnel freezing situation,four schemes are put forward,such as adding insulation layer,setting cold door,developing geothermal and installing de-icing materials.The effects of insulation layer,cold door and developing geothermal are explored by numerical simulation.It is concluded that setting insulation layer at different positions and setting insulation layer with different thickness have poor insulation effect on the entrance of discharge tunnel.Setting cold-proof doors at different door positions of tunnels and discharge tunnels has a good cold-proof effect on tunnels,but the effect of openings is not good;the development of circulating geothermal heat to heat the water flow temperature in the discharge tunnel can achieve good thermal insulation and antifreezing effect. |
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