Study On Multi-Field Coupling Model Of Railway Subgrade In Seasonal Frozen Soil Area

The Qinghai-Tibet Railway around Qinghai Lake,which is located in the seasonal frozen soil area,is prone to frost heave in winter.The frost heave of subgrade brings certain risks to the operation and maintenance of Qinghai-Tibet Railway.The frost heave of subgrade is affected by many factors such as temperature,soil,salt content and moisture.It is necessary to explore the mechanism of various factors such as temperature,soil,salt content and moisture in the process of frost heave.Therefore,based on the frost heave of railway subgrade around Qinghai Lake section of Qinghai-Tibet Railway,this paper studies the multi-field coupling problem of water-heat-salt-force of subgrade.The main research contents are as follows:(1)The subgrade frost damage,environmental climate and soil data were investigated at K222 and K237 mileage of Qinghai-Tibet Railway.The influence factors of water source and water salt migration of railway subgrade in seasonal frozen soil area were explored.The influence of filling gradation,water content and temperature on subgrade frost heave is analyzed.(2)Based on the theory of porous media and the principle of continuous medium,a water-heat-salt-force multi-field coupling model considering negative temperature is established.The mass conservation equation,energy conservation equation and momentum conservation equation of solid,liquid,gas and ice are established.The changes of porosity,adsorption and desorption of salt,ice water phase transition and other effects are considered.(3)Based on the subgrade section at the K222 mileage of the Qinghai-Tibet Railway,the COMSOL Multiphysics multi-physics simulation software is used to model.The temperature curve fitting formula of different depths of the foundation is obtained by fitting,and the subgrade temperature,freezing depth,vertical displacement,water and salt migration and porosity variation are explored.(4)The multi-physical field simulation software COMSOL Multiphysics was used to establish the subgrade models with the height of 2m,3m,4m and 5m.The vertical temperature distribution of subgrade with different heights was analyzed,and the influence of subgrade with different heights on vertical displacement,salt content and porosity in the next ten years was further studied.(5)From the three aspects of subgrade filling improvement method,thermal insulation method and waterproof and drainage method,the treatment measures for subgrade frost heave in seasonal frozen soil area are summarized,and the thermal insulation effect of different heights of thermal insulation road on subgrade is simulated.