Study On The Thermal Conductivity Of Shallow Soil In Xuzhou City

Soil thermal conductivity,especially the thermal conductivity in the field and frozen region,has widely application in underground projects.In this paper,the correlation model of soil thermal conductivity and electrical resistivity is established theoretically.Based on the field test and indoor test on remolded samples,the variations of soil thermal conductivity with soil depth,density,water content and porosity in Fengxian County,Xuzhou,were studied.Based on the formation mechanism of frozen soil,we also studied the variations of thermal conductivity,resistivity and wave velocity under the influence of temperature and analyzed the intrinsic correlation of every two parameters.The main results are as followings.(1)the soil types in the study area are mainly silt and silty clay and the thermal conductivity mainly concentrates on 1.4 W·m-1K-1~1.8W·m-1K-1.The thermal conductivity increases approximately linearly with the water content,and increases with a logarithmic function as the density increases.(2)There is a linear relationship among thermal conductivity,resistivity and density of the silt samples.The thermal conductivity of the sample with 20% water content is higher than that of the other water content.When the water content is below 30%,the thermal conductivity,resistivity and density have a linear relationship with each other.The fitting results of thermal conductivity and resistivity coincide with the correlation model of soil thermal conductivity and electrical resistivity.(3)The thermal conductivity,resistivity and longitudinal wave velocity can be divided into four stages with the change of temperature: pre-phase transformation region,intense phase transformation region,transition region and frozen stable region.The thermal conductivity has a negative exponential relation with resistivity and wave velocity.The wave velocity is exponentially related to resistivity.In the intense phase transformation region,the thermal conductivity increases rapidly and then gradually stabilize.The studies could give guidance to the management of geothermal system and the underground project with heat flow transmission.