Experimental Study On The Thermophysical Properties Of Genhe Silty Clay Under Freezing-thawing Condition

Freezing temperature is an important parameter to judge the frozen or unfrozen state of soil.Dielectric constant is not only the intermediate parameter for determinating the volumetric water content or unfrozen water content by Time Domain Reflectometry?TDR?or Frequency Domain Reflectometry?FDR?technology,but also a vital index to indicate the polarization characteristics of soil.Thermal conductivity is a necessary parameter in the calculation of temperature fields or muti-fields coupling of engineering structures.Therefore,the researches on freezing temperature,dielectric constant and thermal conductivity are important contents for exploring the thermophysical properties of soil.In this paper,some preliminary researches on the freezing temperature,dielectric constant and thermal conductivity of Genhe silty clay were carried out.The main research contents and conclusions are as follows:?1?Based on the tests of temperature-time curves under different temperature control modes,the freezing temperatures of Genhe silty clay were attained.The effects of cooling rates,probe positions,water contetns and salt contents on freezing temperature were studied.Results showed the stages of super-cooling and constant temperature are not obvious if the cooling rate is too fast,but the value of freezing temperature is not affected by cooling rate.There are some differences on the time of free water freezing measured by the temperature probes inserted in different positions of soil sample,the value of freezing temperature is not affected,too.With the increase of water content,the freezing temperature of soil will increase.The freezing temperature will decrease obviously because of the mixing of NaCl or K₂SO₄,and the effect of NaCl is more prominent.?2?The experiments of soil dielectric constants were carried out under dynamic and steady state conditions,and the experimental results under dynamic and steady state conditions were compared carefully.Also,it was proposed that the method of WTT1-5 is more suitful for the determinaton and analysis of dielectric constant of soil.The effects of freezing or thawing process,temperature,water content and salt on dielectric constant were studied.Results manifested the dielectric constant measured in freezing process is greater than that in thawing process at the same negative temperature.When the temperature of soil sample varies in the range of20?⁰?^-10?^-40?,the variations of dielectric constant with temperature can be divided into decrease,rapid decrease and decrease three stages approximately.Dielectric constant will increase with the increase of water content.With the increase of NaCl content,the dielectric constant of NaCl saline soil increase,which is obvious.However,the change of dielectric constant is not prominent when the K₂SO₄ content is not more than 1.5%.?3?Tests on the thermal conductivity of Genhe silty clay with different physical states on the compaction curve were conducted under freezing-thawing condition.The effects of temperature,dry density and water content on thermal conductivity were attained based on the test results.The thermal conductivity decreases linearly with the decrease of temperature in positive temperature range,the influence of dry density and water content on the thermal conductivity is similar,but the influence of water content is slightly more significant,the differences of thermal conductivity of two samples with identical dry density but different water contents are similar.In negative temperature range,the thermal conductivity increases exponentially with the decrease of temperature,and the influence of water content on thermal conductivity is about twice of that of dry density,but the differences of thermal conductivity of two samples with identical dry density but different water contents increase gradually with the decrease of temperature in negative temperature range.?4?Experiments on the thermal conductivity of Genhe silty clay with different contents of NaCl or K₂SO₄ were carried out under freezing-thawing condition.The effects of salt on thermal conductivity were obtained.Results showed the addition of NaCl and K₂SO₄ can reduce the thermal conductivity of soil,but the variation is small.And the thermal conductivity changes inapparently when the salt content increases from 0.5%to 1.0%.The values of thermal conductivity of the soils with the same content of NaCl and K₂SO₄ are highly close at the same temperature.