Experimental Study On Testing And Variation Of Soil Thermophysical Parameters

China is rich in energy resources, while the per capita recoverablereserves is far lower than the world average level. Since2003, China hasbeen the big petroleum consumption country only second to American.Therefore, the development of low carbon economy and renewable energyis the necessary way to social economic sustainable development all overthe world. In the advantage of environment protection, rapid regenerationand can be used circulative, the shallow geothermal energy resources, aswell as the development and utilization engineering of which has becomethe focuses of domestic and foreign scholars. In which, ground source heatpump is so environment friendly and stable, that has been popularized bygovernment in recent years.Heat transfer performance is the key to the design and operation of theground source heat pump. Meanwhile, heat transfer mechanism iscomplicated due to the interaction of solid-liquid-vapor in soil, so it is hardto obtain the thermophysical parameters directly through theoreticalcalculation. Therefore, the physical and thermophysical parameter testsunder the condition of various soil types are necessity for the research onsoil heat transfer performance.This paper study on the variation law of soil thermophysicalparameters through laboratory experiment. Firstly, coarse sand, medium sand, fine sand, silt and clay with different water content was prepared.Secondly, physical parameters such as density, specific gravity, porosityand hydraulic parameter such as coefficient of permeability were tested bybasic experiments. Thirdly, utilizing both thermal probe method and platemethod, thermophysical parameters include thermal conductivity, specificheat capacity and thermal diffusivity were tested. Afterwards the effects ofwater content on soil thermophysical were analyzed based on theexperimental data. In addition, medium sand was selected as example, forfurther research on the influence of porosity and coefficient of permeabilityon soil thermophysical properties.The results have showed that, soil thermal conductivity increased insteps with the increase of water content, which from big to small wascoarse sand, medium sand, fine sand, silt and clay of water content in therange of0~20%. When water content was more than20%, the increase ofmedium sand, fine sand and silt thermal conductivity became to slow down,even slight decreased was observed. While thermal conductivity of claydecreased with water content more than25%. The soil heat capacityincreased with the increase of water content on the whole, especially underthe water content in the range of10%~20%, which increased sharply. Thesoil thermal diffusivity had stage change with the increase of water contentthat, increased with the increase of water content in initial stage, thenstarted to decrease when water content increase to10%~15%for coarsesand, medium sand and fine sand, which was20%for clay.The soil thermal conductivity and heat capacity both decreased withthe increase of porosity under the same water content. While thermaldiffusivity increased with the increase of porosity, but the trend was notobvious until the porosity increased to0.507. Similar to the influence ofporosity, when coefficient of permeability increased, soil thermalconductivity and heat capacity both decreased, and thermal diffusivity increased with the increase of coefficient of permeability.Finally, fitting formulas of the relationship between soil physicalparameters, hydraulic parameters and thermophysical parameters wereobtained by experimental data treatment, and the matching effect werepreferable. The study achievements can provide basic information andtheoretical support for the development and utilization engineering ofshallow geothermal energy resources.