Model Test On Mechanical Characteristics Of Tunnel Portal Section In Cold Region Under Different Water Conditions

There are vast frozen soils in the Qinghai-Tibet Plateau,northeastern and northwestern regions of China.With the great development of the economy,it is inevitable to build tunnels at high altitudes and high latitudes.The survey shows that freezing damage is a major factor affecting the safe operation of tunnels in these areas.By consulting the literature,the author summarizes the research results of the temperature field and stress field of the tunnel in the cold area by experts and scholars at home and abroad,and summarizes the basic theoretical knowledge of the basic theory of the cold area tunnel,heat transfer and frozen soil mechanics.At present,the research results of tunnels in cold regions at home and abroad are quite fruitful,and this paper takes the mechanical behavior of the tunnel section of the cold area as the main research object.Considering the hydro-thermal couple environment of the surrounding rock of the tunnel entrance,the mechanical characteristics of the tunnel portal structure in cold area under different water conditions are studied by indoor model test and numerical simulation.The main research contents and results of the thesis are as follows:According to the similarity theory analysis,a model test of the tunnel section of the cold area with a similar ratio of 1:50 is established.The loess with different water content is used to simulate the surrounding rock under different water conditions,and three test sections are selected along the radial direction of the tunnel.Through freezing test in model box,the distribution of temperature field in different sections of surrounding rock and tunnel lining during freezing process,radial and circumferential stresses of lining,horizontal frost heaving force on the back of end wall portal wall,and deformation law of portal and slope are measured.The test results show that with the increase of water content,the freezing rate of surrounding rock becomes faster,the horizontal frost heave force of the portal wall increases by 12%,the circumferential stress of tunnel lining increases by 10.5%,the radial stress increases by 9.2%,and the portal and slope the displacement increased by 11%.The ANSYS thermo-mechanical couple numerical simulation of the tunnel cavity test model is carried out to analyze the distribution law of the model temperature field under different water conditions,and compared with the model test results.The circumferential and radial stress of the lining is studied.The distribution law of horizontal frost heave force,as well as the displacement deformation law of the portal door and the slope,compare the results of the numerical simulation with the results of the model test.The results show that compared with the model test,the temperature reduction rate of the numerical simulation is faster;the horizontal frost heaving force of the back wall of the model test and the numerical simulation has a 23.5% error,and the variation of the circumferential and radial stress of the lining is similar to the model test.The error is about 20.2%,and the displacement of test error betweenthe gate and slope are 22.8%.This paper provides a basis for the study of the mechanical properties and antifreeze technology of other typical cave doors in the cold area under the freezing and thawing cycles.In this paper,the structural characteristics of tunnel portal section in cold area are studied by model test and numerical simulation,which provides a reference for studying the mechanical characteristics and antifreeze technology of other typical cave doors in cold area under freezing and thawing cycles.