Study On Formation And Evolution Of Freezing Tunnel

After the Sichuan-Tibet Railway is expected to be completed,a number of cold tunnels will be added.According to the previous freezing tunnel construction experience,after the tunnel construction is completed,the non-frozen soil section and the non-permafrost soil of the permafrost tunnel will appear during use.The freezing front of the tunnel spreads and freezes over the entire length of the tunnel over time(referred to as the gradual freezing phenomenon),causing the lining wall to fall off,resulting in damage to the structure and use of the tunnel,and even causing the tunnel to be scrapped to the people in the disaster area.The safety of life and property poses a serious threat.This article is based on the National Natural Science Foundation project "Research on Evolution and Catastrophe Control Methods of Gradual Freezing Tunnels".With the background of tunnel gradual freezing disasters,based on basic heat transfer theory such as basic heat transfer equations and energy conservation laws,the The commonly used dimensional analysis method is used to derive the similarity criterion for the heat transfer process of the temperature field of the tunnel heat transfer model.The similarity criterion numbers of several main heat transfer process indexes of the gradual freezing tunnel are obtained,and the similarity ratio of the corresponding physical quantity is obtained.,Determine the tunnel gradual freezing criterion;designed and developed the indoor physical simulation test equipment of the gradual freezing tunnel,and prepared similar to the thermal physical parameters of a section of the surrounding rock of the non-frozen soil section of the cold tunnel in the domestic typical gradual freezing disaster.The surrounding rock materials,similar simulation model tests were carried out under the conditions of ventilation and seepage,and the temperature field of the tunnel during the freezing process was studied.The study found that:(1)Under the environmental conditions of global warming and constant temperature increase,the radial radial freezing mode of the tunnel: the radial freezing front in the surrounding rock of the tunnel mainly advances in the direction of the increase of the buried depth of the tunnel,and then forms a gradually frozen thickening from inside to outside Freeze the wall.The freezing modes of the dome,left and right arches and the upward arches are slightly different,mainly reflected in the burial depth of the interface of the freezing mode;the radial gradual freezing mode of the tunnel under long-term conditions: the radial freezing front in the tunnel surrounding rock mainly follows the tunnel The depth of the burial depth increases,and a frozen wall that gradually freezes and thickens from inside to outside is formed.This process continues until 600 months.That just says,after the 50 th year,the cooling process of the entire surrounding rock surface basically ends and changes.For the heating process,it will eventually rise to the state where the surrounding frozen soil is completely melted;(2)Under the environmental conditions of global warming fluctuations and warming,the radial gradual freezing mode of the tunnel: the radial gradual freezing mode of the gradual freezing tunnel is mainly that the surrounding rock gradually freezes along the direction of the burial depth growth;(3)Under the conditions of global warming fluctuation and temperature rise,the temperature distribution evolution law of radial surrounding rock when the tunnel in the cold area is gradually freezing: the temperature gradient,heat flux density and heat flux of the deep surrounding rock of the tunnel are roughly divided into two stages.In the first stage,the temperature of the surrounding rock has never been completely disturbed to complete disturbance,and the temperature gradient,heat flux density and heat flux gradually increase until it reaches the peak;in the second stage after the surrounding rock temperature is completely disturbed,the temperature gradient,heat flux density and heat flux The presentation gradually decreases.From the temperature change of each layer in the first year and the gradual melting temperature rise in the later 60 years,the temperature of the surrounding rock of different embedding depths shows a rising trend with the temperature change in the tunnel.As the surface distance increases,the amplitude of its fluctuations is still decreasing,but the law of temperature increase is relatively close.The temperature in the stratum with a small temperature gap will gradually converge during the temperature increase process,which causes the cold area tunnel to gradually Frozen;During the process of global warming and warming of the tunnel,the temperature field of the surrounding rock of the tunnel exhibits an obvious periodicity.The maximum freezing depth at the entrance of the tunnel appears in the 50 th month(4.2 years)after the tunnel is opened and its minimum temperature It reaches-3.2;the farther away from the tunnel entrance,the lowermost point lags behind.The lowest point of the temperature at the exit after the entrance to 400 meters is roughly delayed by 24 months(2 years),and the lowest temperature value is 0.2.(4)The gradual freezing mode of the gradual freezing tunnel longitudinal section under the conditions of global warming fluctuations and warming is: the tunnel gradually freezes from the entrance to the exit of the tunnel,and after a fixed time interval(the time interval at different burial depths is different,the burial depth For example,at 4m,every 100 months,the tunnel will have a gradual freezing disaster of 200 months.The smaller the burial depth,the longer the cyclic freezing disaster will last.)The gradual freezing disaster will occur in the surrounding rock,and The cycle occurs repeatedly.(5)The evolution rule of the longitudinal section of the gradual freezing tunnel under the conditions of global warming fluctuations and temperature rises: Under the influence of natural small temperature amplitude and temperature,periodic gradual freezing and thawing disasters will occur at the entrance of the tunnel,and the occurrence of gradual freezing disasters The time interval and duration decrease with the increase of the embedding depth;(6)The monitoring results obtained in this study can be obtained through comparison and analysis with the theory and numerical models of other experts and scholars,which are in good agreement with the results of other experts and scholars,proving that the test device can The actual measurement verification has a good simulation effect.Its self-generated temperature control system can simulate the temperature distribution of any thermodynamic working condition.Combined with the basic thermodynamic parameters of the surrounding rock on site,it can be used for the construction of tunnel projects in similar cold areas around Qinghai.Provide reliable guidance.