Study On Water Migration In Unsaturated Frozen Soil Under Snow Melting

China is the third largest frozen soil country in the world,and there are a lot of seasonal frozen soil areas.Because of the global warming,the temperature in seasonal frozen regions is increasing,and snow melting is increasing.This phenomenon has lead to many seasonal frozen soil natural slopes,highway and railway subgrade often due to snow melting infiltration caused by sliding and other safety accidents.It brought serious losses to the affected areas,such as traffic,economy,industry and agriculture.Therefore,the study on the stability of seasonal frozen soil slope under the condition of snow melting infiltration is of great significance to the prevention and control of seasonal frozen soil engineering diseases.Under the action of snow melt infiltration,the shallow water content and matric suction of soil changed,resulting in water migration in the soil,which then affected the soil stress field,reduced the shear strength of the upper soil,and finally caused disasters.Therefore,the study of water migration in seasonal frozen soil under the effect of snow melting infiltration is the premise to study the stability of unsaturated seasonal frozen soil slope under the effect of snow melting infiltration.Based on Darcy’s Law and the law of conservation of energy,this paper deduced the waterthermal coupling equation and the water-thermal connection equation of unsaturated frozen soil.The water-thermal coupling model was obtained by numerical simulation software,and the snow melting and infiltration conditions were introduced.Unsaturated soil in western Sichuan was taken as the research object.The influence of the relative content of coarse and fine particles(represented by the difference of coarse material content)on the hydrodynamic characteristics parameters(permeability coefficient,soil-water characteristic curve parameters)was taken into consideration and brought into the model to analyze the temporal and spatial variation law of unsaturated soil water field in western Sichuan.The main work and research contents of this paper are as follows:(1)The soil is regarded as a porous medium,through the change of water flux and heat in a micro element,combined with Darcy’s law,energy conservation law,etc.,the onedimensional water-heat coupling equation and water-heat connection equation of unsaturated frozen soil are derived,providing a theory for the establishment of water-heat coupling model.(2)Transform the derived water-thermal coupling equation and the water-thermal connection equation,get the coefficients in the form of coefficient type partial differential equation,and define the solid-liquid ratio,water diffusion rate,permeability coefficient and other parameters in the form of piecewise functions,and then use COMSOL Multiphysics PDE secondary development.The coupling numerical simulation of unsaturated soil moisture field and temperature field is realized.The numerical simulation was applied to the freezing and thawing test of one-dimensional soil column under closed conditions.The feasibility and effectiveness of the numerical simulation were analyzed by comparing the measured data.(3)According to the hydrothermal coupling equation,it is concluded that the hydrothermal parameters of unsaturated soil should be studied to obtain the value or change rule of the permeability coefficient,soil-water characteristic parameters,volumetric heat capacity,thermal conductivity and other parameters,which can be substituted into the hydrothermal differential equation to provide a parameter basis for the establishment of the hydrothermal coupling model.(4)Taking unsaturated soil in western Sichuan as the research object,the slope model under snow melting condition was established.According to the calculation results of the model,the variation law of temperature and water field of unsaturated slope is analyzed,which provides a reference for the study of frozen soil slope stability and disaster prevention under the condition of snow infiltration.(5)Based on the slope model under the condition of snow infiltration established by soil parameters with different coarse particles content,the variation of soil moisture content in slope with different coarse particles content was studied,and its influence on water migration was analyzed,which provided a reference for the stability study of seasonal frozen soil slope in western Sichuan under the condition of snow melting.