Study Of Characteristics Of Unfrozen Water Content And Moisture-heat Coupling Model For Frozen Soil In Qunli Area Of Harbin

The permafrost area in China accounts for 21.5% of the land area,of which the seasonal permafrost area even reaches 53.5% of the land area.Along with the rapid development of economy in China,it has become increasingly important for the development of resources and engineering construction in frozen soil areas.Damage caused by water migration in frozen soil is the primary problem in engineering in frozen soil areas,and this freezing injury is the result of multi-field coupling of frozen soil.The study of coupling mechanism of frozen soil involves many disciplines.A large number of parameters are needed to describe the freezing process in numerical simulation,and the values of these parameters would change with the freezing process,which makes it difficult to apply to practical engineering.In this paper,the characteristics of unfrozen water content and moisture-heat coupling model of frozen soil were studied based on nuclear magnetic resonance and one-way freezing test.The specific research contents and results are as follows:Measure the unfrozen water content and temperature variation curve of frozen soil through nuclear magnetic resonance test,this paper analyzed the freezing process of soil samples according to the test data,and studied the characteristics of unfrozen water content of frozen soil.Taking the relative saturation of soil samples as independent variables,the freezing characteristic curve between relative saturation and matrix suction was obtained by using the relationship between matrix suction and temperature in Clapeyron equation and nuclear magnetic resonance test data.Based on Fourier law,mass conservation principle and Darcy law,the governing equations of temperature field and water field of frozen soil were derived.The values of thermal parameters in the hydrothermal coupling model were analyzed and determined,and the permeability coefficient,hydraulic diffusion coefficient and solid-liquid ratio parameters were obtained by fitting with nuclear magnetic resonance test data.The closed one-way freezing test of clay and fine sand soil columns was carried out by using freeze-thaw cycle test chamber,and the temperature field and water field data during the freezing process of soil columns were obtained.There are obvious cracks,water accumulation and uneven distribution of ice in soil columns after freezing.After freezing,the temperature of the center point of the soil column changes linearly from the warm end to the cold end,the water content at the cold end decreases and the water content at the warm end increases.Firstly,the moisture-heat coupling model of clay and fine sand soil column was established,and the temperature field and water field of soil column were calculated,which are compared with the results of one-way freezing test to verify the accuracy of the model.After that,the temperature field and water field distribution of soil column under variable temperature condition were calculated,and the simulation results were compared and verified.Finally,the water field and temperature field of subgrade were calculated through the hydrothermal coupling model,and the variation law of temperature,unfrozen water content and ice content with freezing time was analyzed.