Coupling Analysis Of Moisture And Heat In Strong Weathered Surrounding Rock Tunnel In Deep Season Frozen Soil

China is a large country with permafrost,more than half of the country's land belongs to permafrost regions that have an impact on the project.With the rapid development of our economy,the transportation network has begun to expand to remote permafrost regions such as northeast and northwest,but the topographies of these regions are mostly mountains and hills,thus the construction of tunnels are the key to solving traffic problems.Many tunnels have been built and under construction in Chinese permafrost regions,but due to the harsh environment,many tunnels have severe freezing damage problems.The major cause of freezing damage in tunnels is that freezing-thawing cycles will occur in the surrounding rock of the tunnel in cold areas,which will cause damage to the tunnel structure,and then seepage phenomenon will occur,and ice formed by seepage water will increase the freezing damage in turn.Therefore,for the prevention of tunnel freezing damage,considering the surrounding rock moisture-temperature coupling and obtain the distribution law of the temperature field and moisture field of the surrounding rocks is the key to prevent freezing damage.Relying on the Xinganling tunnel in the deep-season frozen soil area,the basic physical property test and unidirectional freezing test of the strongly weathered surrounding rock at the entrance of the tunnel are carried out to obtain the basic properties and freezing characteristics.The moisture-temperature coupled model was established and the correctness was validated.Finally,a two-dimensional model of the tunnel is established to calculate the coupling of the temperature field and moisture field of the surrounding rock of the tunnel,a reference for the prevention of tunnel freezing damage in deep season frozen soil is provided.The research contents and results are as follows:Firstly,the basic physical properties of the strongly weathered surrounding rock soil in Xinganling tunnel were tested,and the basic physical properties of the surrounding rock soil were obtained,including the particle density,particle grading,limit moisture content,maximum dry density,permeability coefficient,thermal conductivity and heat capacity.The results show that the grade distribution of the strongly weathered surrounding rock is good,the clay content is a little high,the temperature and filling water conditions have great influence on the freezing.The higher the temperature gradient,the faster the freezing.Secondly,based on the law of conservation of energy and mass,the partial differential equations of temperature field and moisture field were derived from the differential point of view.Based on the Harlan model,the moisture-thermal coupling model of saturated permafrost was established to simulate the freezing process of saturated one-dimensional soil column,and the validity of the model was verified by comparing with the test results.The effects of phase transition and filling water conditions on moisture-thermal coupling were simulated and analyzed.The calculation results show that the heat generated by the phase transformation of water into ice inhibits the transference of cold energy,which slowed the temperature change of soil,so the temperature change rate in an open system is less than that in a closed system.But when the system is in equilibrium,the temperature distribution is uniform,mass exchange with the outside world because of the temperature gradient,the total water content in the open system is greater than the initial state.Finally,based on the moisture-thermal coupling theory,a two-dimensional tunnel numerical model was established to realize the complete coupling of the temperature field and moisture field of the tunnel considering the phase transition,and the influence of the permeability coefficient on the coupling of the temperature field and moisture field was analyzed.The variation law of the thickness of the frozen ring in the tunnel of xingan mountains was calculated,considering the seepage effect,the temperature is higher than that without considering the moisture field,the larger the permeability coefficient is,the greater the influence will be,which can provide the reference for the geotechnical.