Experiment And Numerical Simulation Analysis Of Water And Heat Transfer Of Silt Soil In Cold Area Under Freezing

The soil in the cold area is affected by the temperature.Under the action of low temperature,the phase of the water in the soil changes,forming a phenomenon of frost heave and thaw,which has an adverse effect on construction projects.But at the same time it is also easy to cause spring flood disasters.The main reason for the occurrence of these disasters is that the water migration during the freezing process leads to the redistribution of the water field and the change of phase state under the influence of low temperature.Therefore,it is of great significance to study the soil water and heat migration in cold regions.In this paper,a silty soil is taken as the research object,a set of large sample unidirectional freezing test device is developed by itself,and the unidirectional freezing test under closed conditions is carried out for the two factors of freezing temperature and initial moisture content.The temperature is monitored in real time,and the PDE module in COMSOL Multiphysics software is used to numerically calculate the water-heat coupling equation of the frozen soil in the unsaturated state,and then to analyze the water and heat transfer law of the silty soil in the cold region under freezing.Through research,the following conclusions are obtained:(1)The change of soil temperature can be divided into three stages: rapid descent period,descent gradient slowing period,and tending to stable period,and the duration of each stage increases with depth.The lower the freezing temperature,the deeper the maximum freezing depth,the faster the temperature drop rate,the longer the temperature field stabilizes,the greater the water migration rate and water migration;the greater the initial soil moisture content,the duration of each stage of the temperature field The longer the temperature stabilization time,the lower the temperature drop rate,the slower the migration rate of the frozen front,but the greater the water migration flux.(2)The change of soil unfrozen water content is divided into three stages: the rapid decline period,the decline rate slows down period,and the stable period;the lower the freezing temperature,the more drastic the change in unfrozen water content,the more the water migration rate and migration flux The larger,the slower the advancing rate of the freezing front;the temperature potential difference has a significant effect on water migration.The larger the potential difference,the greater the migration amount and migration rate.(3)The water and heat coupling model of frozen soil is basically consistent with the actual test law distribution.It is reliable to use the model to calculate and analyze the water field and temperature field of different initial conditions,which has certain reference significance for the study of soil water and heat transfer in cold regions.