The Instrumental Development Of Thermal Conductivity Of Frozen Ground And The Research On The Steady-State Method Simulation Test

In physics, thermal conductivity is the property of a material that indicates its ability to conduct heat. Generally speaking, it can be determined by two ways in theory and experiment. Theoretically, the thermal conductivity through clear mechanism to determine the thermal conductivity of physical model for the more complex mathematical analysis and calculation will be obtained. So far, except for a few substances, such as certain gases, liquids, pure metal, it is also difficult to calculate in advance the theory of thermal conductivity material. On the other hand through the experiment measuring the thermal conductivity, which is the main way to determine the thermal conductivity and the only way to study material thermal properties. So researchers at home and abroad take a great deal of scientific research, and gradually formed and developed a systemic thermal conductivity measurement theory and the effective experimental technique.With rapid economic development, the number of projects is growing up in permafrost regions, such as the Qinghai-Tibet Railway and the Sino-Russian oil pipeline project etc, which need to research the thermal properties of frozen soil, closely related to the projects, as the important basis in designing and maintaining subsequently. In addition, with the relative shortage of energy today, geothermal energy as a new energy is more and more attached by people. In the process of developing geothermal energy, the thermal properties understanding of geothermal wells surrounding soil and filler are a primary task, so the research on the thermal conductivity of the soil has extremely important significance; furthermore the cooling solving of buried cables also needs to study the thermal conductivity properties of surrounding soils.The thermal conductivity of frozen ground , the important index in researching the frozen ground thermal property ,is designed for the calculation of both heat quantity circulating in the natural soil body freezing and thawing depth and temperature field , and also used in heat engineering calculation related to architectural engineering in frozen soil field. As far as its testing methods are concerned, there are two main methods steady-state and unsteady-state among diverse kinds, and the former is used in this paper, which is so-called the heat-flow meter method.The paper mostly includes two parts, one is the instrumental development of the heat-flow meter method, and another is analysis and comparison of the test data. In the first part, the paper introduces the heat-flow meter method instrumental development course including the amelioration of the soil sample case, the coat of heat preservation and pipeline heat preservation technique improvement. Eventually, the instrument was satisfied with the national and the industrial standard at the accuracy less than 5%.In the second part, the paper discusses on the thermal conductivities of frozen/unfrozen ground of the gravel containing fine soil and silty clay in the different state of water capacity and dry density.1) In the same dry density, the thermal conductivities of frozen/unfrozen ground of the gravel containing fine earth increase approximately linearly along with water capacity.2) In the same water capacity, the thermal conductivities of frozen/unfrozen ground of the gravel containing fine earth increase approximately linearly along with dry density.3) The thermal conductivity of frozen gravel containing fine earth keeps more than that in unfrozen state, as the water capacity ranges from 8% to 20% and the dry density ranges from 1.7 to 1.9g/cm3.4) In the same dry density, the thermal conductivities of frozen/unfrozen silty clay increase approximately linearly along with water capacity.5) In the same water capacity, the thermal conductivities of frozen/unfrozen silty clay increase approximately linearly along with dry density.6) Silty clay appears different from gravel containing fine earth in this characteristic. In a smaller dry density scale, the thermal conductivity of unfrozen silty clay is higher than frozen soil's in some small value water capacity which gradually dwindles as the increase of dry density.In the end, It can get the conclusion by comparing the test values in the simulated test with the values in code.1) As for the comparison of the thermal conductivity between frozen/unfrozen ground the gravel containing fine earth and gravelly sand in the code, the values are close in theory, because the content of grain are both larger than 85% .However, the norm values of thermal conductivity of gravelly sand in code are higher than the values of gravel containing fine earth in the test which are more reasonable and accurate.2) As for the comparison of the thermal conductivity of frozen/unfrozen silty clay between in the simulated test and in code, the values of homogeneous soil are generally the same. It finds that the values of silty clay in code are higher, while the data from the heat flow meter relatively agree to the characteristics of silty clay.In this paper, the innovations are adding the thermal conductivity of gravel containing fine soil frozen and unfrozen state, and amending the thermal conductivity of silty clay.