Study On Influencing Factors Of Thermal Conductivity Of Changchun Area Silt Clay

Thermal conductivity of soil is an important parameter involved in the pre-design of geothermal engineering and solving all kinds of temperature field problems.The soil is composed of triphase material of soil particles,water and air,and its thermal conductivity is related to the thermal conductivity of triphase material itself,but the research shows that the basic physical parameters reflecting the proportion of triphase material composition of soil have a more significant effect on the thermal conductivity.In view of this,it is of great guiding significance to quantitatively analyze the correlation between basic physical properties and thermal conductivity of soil and its thermal conductivity mechanism in order to make more scientific use of this parameter for engineering design.In this paper,the typical silt clay of Changchun area was used as the research object.At 36 experimental points in Changchun,40 sets of undisturbed soil sample were taken using investigation drilling.Through laboratory experiments,the thermal conductivity,porosity and moisture content of undisturbed soil and reconstructed soil were tested,multivariate linear regression fitting of thermal conductivity and physical parameters using SPSS statistical analysis software,multivariate fitting effect was good,independent variable could explain the variation of the dependent variable well,and the correlation between thermal conductivity of Changchun area typical silty clay and porosity and water content was obtained.In order to study the influence of single factor on the thermal conductivity of soil,19 groups of reconstructed soil samples were made from the original soil as raw materials,and the variation law of soil thermal conductivity with basic physical parameters is obtained: thermal conductivity increases with the increase of water content,the whole growth trend tends to stabilize gradually from the rapid growth,with the increase of porosity,thermal conductivity decreases linearly,the R2 of multivariate fitting results is 0.869,and the fitting effect is good.The multivariate fitting relationship of the relevant data obtained by the undisturbed soil and the reconstructed soil is the same,in which thermal conductivity of the soil is positively correlated with the water content and negatively correlated with the porosity.The results of laboratory experiments show that under the condition of controlling another variable,there was a positive correlation and negative correlation between thermal conductivity and water content and porosity of undisturbed soil,and multivariate fitting effect is good,and independent variables can explain the variation of dependent variable well;thermal conductivity of remodeling soil increases with the increase of water content,the whole growth trend tends to stabilize gradually from rapid growth,and with the increase of porosity,thermal conductivity decreases linearly,and the R2 of multivariate fitting results is 0.965,and the fitting effect is good;the expression forms of two multivariate fitting relations are the same,among which thermal conductivity of soil is positively correlated with moisture content,and porosity was negatively correlated.Under the condition of controlling other influencing factors,thermal conductivity of soil decreases with the increase of porosity.According to descent rate can be roughly divided into three stages,when porosity is less than 45%,thermal conductivity decreases slowly with increase of porosity,porosity increases by 5%,thermal conductivity decreases with a decrease amplitude of less than 5%;when porosity range is within 45%~60%,with the increase of porosity,thermal conductivity decreases with decrease amplitude 8%;when the porosity exceeds 60% and increases,thermal conductivity decreases rapidly with a decrease amplitude of more than 10%,and the decrease amplitude is increasing.When water content and porosity are controlled,thermal conductivity increases gradually with the increase of temperature,and there is a linear relationship between the two.Finally,the influence of soil microstructure parameters on thermal conductivity is studied from the microscopic point of view.Taking some undisturbed soil samples,the SEM images of microscopic soil samples were obtained by microscopic scanning electron microscopy,and the microscopic parameters such as pore shape factor,pore probability entropy,regional probability distribution index and pore fractal dimension of soil samples were further obtained,and the influence of microscopic parameters on the thermal conductivity of soil was analyzed.Among them,thermal conductivity of soil decreases with the increase of pore shape factor,pore probability entropy and pore fractal dimension,and becomes larger with the increase of pore regional probability distribution index.It shows that the shape of soil particles tends to be sharp and narrow,the connection between them weaken,thermal contact resistance between particles increases,and thermal conductivity decreases;the arrangement of soil particles and pores is gradually changed from order to random arrangement,which results in the weakening of soil particle connection,the increase of contact area between soil particles and pores,and the decrease of thermal conductivity;the proportion of pore per unit volume increases,the soil particles decrease,and thermal conductivity decreases.However,the number of large pores in the unit area decreases,the connection between soil particles is closer,the proportion of air in the thermal path decreases,and thermal conductivity of soil increases gradually.