Laboratory Experiment And Numerical Simulation Of Soil Water Freezing And Thawing Mechanism

There are complex water-heat migration laws and mechanisms in the process of freezing and thawing.In order to study the variation law of soil moisture content,temperature and thermal conductivity during soil freezing and thawing,the sand column of water-heat change law in the process of freezing and thawing Experimental studies were carried out,and the experimental results were simulated and predicted using the SHAW model(soil hydrothermal model).The soil water-heat change research experiment uses quartz sand as the medium,fills the plexiglass column with the weight according to the weight,puts the soil column into the freeze-thaw cycle box,and performs one-way freezing of the soil column by controlling the temperature change;using 5TM sensor Real-time monitoring of the vertical temperature of the soil column during the freezing and thawing process,the change of water content during the freeze-thaw process.Experiments show that the soil freezing process is an exothermic cooling process.The heat transfer direction in the sand sample is from the deep to the shallow part.The frozen front in the shallow soil will gradually migrate downward.At the frozen front,liquid water will be converted into The phase change phenomenon of ice,at this time,a part of the heat will be released(the solid-liquid phase will become hot).Since the temperature of the shallow sand sample is much lower than the depth of the soil column,a part of the liquid water will accumulate at the frozen front.Will make the heat transfer faster,so the soil column freezing process will last longer.The volumetric water content of each layer of soil experienced a sharp decrease,stable and slowly rising process;after a freeze-thaw cycle,the water inside the soil column has an upward migration tendency,and the water content at 10 cm and 15 cm has a obviously water accumulation phenomenon,and the moisture content of the soil sample at 20 cm deep is reduced.This is because when the freezing front moves downward,the temperature of the bottom of the soil column is higher than the temperature of the middle part,resulting in an upward temperature gradient.Under the force of a temperature gradient,a part of the water will migrate upwards,and the moisture content will be increased at the frozen front.From the experimental data analysis,after the soil is completely frozen,there will still be some liquid water.These may be the combined water stored in the pores and the extremely difficult to freeze liquid water attached to the ice.Using KD2 Pro thermal conductivity meter to monitor the change of thermal conductivity during multiple freeze-thaw cycles,the experimental study found that the thermal conductivity of sand sample increases with the increasing of soil volume and water content;when the volumetric moisture content of three sand samples When they are all the same,the thermal conductivity of the soil will increase with the increase of the dry density of the soil;under the same water content,the thermal conductivity of the frozen state will be much larger than that of the melted state,and the water content will be The higher the rate,the more obvious this phenomenon is.The SHAW model was combined with the existing experimental data to simulate the soil temperature and soil moisture content more extensively,and the hydrothermal migration law of sand column under saturated state was preliminarily explored.The results show that the model can fit the soil moisture content and temperature well,and can predict the depth of soil freezing in each time period,which can be used to simulate the hydrothermal simulation of deeper soil.This paper provides the basic test procedures and cases for the indoor test of soil freezing and thawing process,and combines the preliminary experimental results to explain the phenomenon of water and heat migration and physical processes during the freezing and thawing process.