Study On Deformation Of Upward Slope At Tunnel Portal Of Railway Tunnel In Frozen Soil Area

There are large areas of permafrost in Northeast,northwest and Qinghai Tibet Plateau of China.Permafrost has the characteristics of rheological property and instantaneous strength far greater than long-term strength.In addition to the complex and changeable external climate environment in these areas,the engineering structure construction in permafrost areas must also face two main dangers: frost heave and thaw settlement.These disasters not only lay a hidden danger for the later engineering construction,but also restrict the economic development of the region.In recent years,more and more railway tunnels have been built in permafrost areas in China,and the instability and failure of various slopes are increasing.Tunnel portal section is often one of the areas that lead to collapse,cracking and damage.Therefore,the stability of the side slope of the portal section must be taken seriously in the design and construction of the tunnel.It is of great significance for the tunnel construction and the completion of the engineering theory in these areas to carry out the relevant research on the tunnel in the cold region.In this paper,the tunnel portal side slope is taken as the research object,considering the thermal parameters of frozen soil and the coupled environment of water and heat of the surrounding rock in the tunnel portal section.Through the establishment of indoor model test and the use of ANSYS numerical simulation,the deformation characteristics of the tunnel portal side slope in cold area under different water content and different slope angle are studied.The main work of this paper is as follows:Based on the literature of related tunnel engineering,the physical mechanics and thermodynamics parameters of soil mass changing with temperature are obtained,and the basic theoretical knowledge of tunnel,frozen soil mechanics and heat transfer in frozen soil area are summarized.A tunnel model with a similarity ratio of 1:50 is established by referring to the similarity theory.The selected soil sample is hard plastic and silty clay.Through the freezing process in the model box,the freezing process of tunnel portal section is measured The change of temperature field,stress field and displacement field in the junction process.The thermal mechanical coupling analysis of the tunnel test model is carried out by using ANSYS finite element software.The temperature field,stress field and displacement change law of the model under different water content and different slope angle are explored.The numerical simulation results are compared with the test results.The results show that: the results of temperature field in laboratory test and numerical simulation are basically consistent;the horizontal frost heaving force obtained by numerical simulation is larger than the results of laboratory test,with an average error of about 10%;with the increase of water content,the horizontal frost heaving force under the two analysis methods increases by about 12%;thedisplacement and deformation measured by laboratory test are respectively 1.93 mm and2.24 mm,and the most important one in numerical simulation The large displacement is2.07 mm and 2.4mm respectively,and the average error between the freezing test results and the numerical calculation results is about 7%.With the increase of the tunnel slope angle,the displacement deformation of the slope also increases,and the slope angle is proportional to the change of displacement.