Hydrothermal Coupling Model And Numerical Simulation Of Unsaturated Frozen Soil

Due to the drastic changes in the external environment temperature,the rock and soil bodies repeatedly freeze and melt,resulting in cracking,dumping,and even collapse.The study of the problem of water-heat coupling of frozen soil aims to reveal the mechanism of frost heaving and melting of unsaturated rock soil,and provide theoretical guidance for the design of frozen soil and the prevention and control of frozen soil diseases.In this paper,the hydrothermal coupling problem of unsaturated frozen soil is studied.Firstly,the frozen soil experiment is carried out to obtain the basic physical parameters of the soil sample.The nonlinearities of soil specific volume heat capacity,thermal conductivity,unsaturated seepage coefficient,specific water capacity and water diffusion coefficient were obtained by empirical formula.Mathematical expression;based on Fourier’s law,mass conservation equation,and the basic theory of Richards equation,the two-field correlation equation of frozen soil water and heat is introduced,and the hydrothermal coupling model of unsaturated frozen soil is established.The PDE interface is second through Comsol Multiphyscis software.The influence of initial moisture content and warm end temperature on the ice content of pores was studied.The influence of annual temperature conditions on the temperature field and water field distribution of unsaturated soil roadbed and the latent heat of phase change on frozen soil water were studied.The thermal coupling temperature field affects the law.The main conclusions are as follows:(1)When the external water supply is not considered,the total moisture content of the test clay is always saturated water content.At this time,the volume specific heat capacity is linearly positively correlated with the liquid water content;the thermal conductivity is negatively correlated with the liquid water content;the saturated seepage coefficient and the water diffusion coefficient increase sharply with the increase of the liquid water content in the exponential form.The specific water volume increases first and then decreases with the increase of the liquid water content.(2)The change of initial moisture content and warm end temperature will affect the distribution of ice content in soil pores.The initial moisture content change only affects the distribution of pore ice content in the frozen zone,but has little effect on the temperature field,that is,the location of the freeze-thaw interface does not change,but the temperature change of the warm end affects both the temperature field and the water field of the soil column.Solid ice accumulates more.(3)The outside temperature only affects the temperature field within 0-5.8m of the subgrade.The temperature rises or falls within one year,the winter of the 0-0.27 m seasonal active layer occurs,and the liquid water of the frozen soil in summer season gathers.The water content is up to 0.4.At this time,the excessive accumulation of moisture is likely to cause the surface of the subgrade in the cold area to be pulverized;in the winter season,the liquid water in the frozen soil layer is reduced,and the ice content of the pores is increased from 0.2 to 0.4,and the flexible pavement is prone to uneven bulging or cracking.Phenomenon,in the permafrost layer,the temperature change will cause a small change in the temperature field and water field in the range of 0.27-5.8m,and the range is more than5.8m.Since the surface temperature of the flat slope is less than the surface temperature of the slope,the slope is prone to melting and sinking in summer.(4)The latent heat of phase change has a great influence on the water-thermal coupling temperature field distribution of the subgrade.The latent heat energy of the phase change significantly reduces the influence range of temperature on the subgrade temperature,the freezing and thawing interface of the subgrade rises,and the temperature rises(or falls),considering the phase.The temperature rise(or decrease)of the submerged heat road base is slow,and the response to temperature is poor.The latent heat of phase change is beneficial to the upper limit of permafrost.