Hydrothermal Coupling Analysis Of Premelting Technology Of High Temperature Frozen Soil Foundation In Permafrost Regions

With the global warming,the island-like frozen soil in the permafrost regions of Northeast China is seriously degraded,causing the bearing capacity of the foundation to decrease,causing uneven settlement of the roads;and geological disasters such as landslides and debris flow caused by the degradation of frozen soil is not uncommon.In combination with the annual average temperature in Northeast China,the principle of protecting frozen soil is no longer applicable.In response to this situation,some scholars have proposed that for high-temperature frozen soil,pre-melting frozen soil can be used to alleviate the disaster caused by the degradation of frozen soil.Frozen soil is sensitive to water content and temperature,therefore,the research on the water field and temperature field inside the soil during the pre-melting process and its coupling effect has important practical significance.At the same time,in the judgment of the heat and moisture migration inside the frozen soil,the specific heat capacity,thermal conductivity and unfrozen water content of the soil are necessarily used,based on this background,the main research contents of this paper are as follows:(1)It is proposed to apply DSC(differential scanning calorimeter)to the thermal analysis test of frozen soil,verify its feasibility,and summarize a set of temperature rise and fall rates and sample preparation methods suitable for the specific heat capacity test of frozen soil;The effects of dry density and initial moisture content on the specific heat capacity and thermal conductivity of frozen soil were established.The formula for calculating the specific heat capacity of frozen soil containing latent heat and sensible heat was established.(2)A new method for measuring unfrozen water was proposed by the accurately record of heat flow during the experiment,the results of unfrozen water tested by DSC and NMR(low field nuclear magnetic resonance)measurement are compared to verify the accuracy of this method.Based on this,a calculation model for the unfrozen water content during the melting process was established.(3)Based on the Darcy's law of unsaturated soil and the basic criterion of Fourier heat transfer,the water motion control equation of the water vapor movement inside the soil is deviated in the three-dimensional case,and the water content is variable;in the same dimension,The ice-water phase transition during freezing and thawing is treated as internal heat source,and the temperature control equation considering heat conduction and convective heat transfer is derived.Finally,the relationship between the unfrozen water content and temperature in the melting process is taken as the simultaneous equation,and the spatial three-dimensional is established.Hydrothermal coupling model during the melting of frozen soil under conditions.(4)Based on the secondary development of finite element software COMSOL Multiphysics,the temperature and water transfer laws during the melting process in the presence of heat source in frozen soil are analyzed.Finally,the indoor model test results are compared with the simulation results to further verify the established.The reliability of the hydrothermal coupling model.