Development of a system for measuring local thermal conductivities of surface soil in situ.

概要

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Thermal properties of soil have been greatly concerned in the various fields of science and engineering. Geothermal energy development technology, also, requires detailed information on the dependence of thermal properties of surface soil on depth to evaluate geothermal potential exactly by measuring surface soil heat flow at an early stage of the development activities. Generally, thermal properties of soil have been measured in laboratory with samples gathered from fields. But its values are different from that of in situ, because the samples don't have same soil structure, and temperature and moisture conditions in situ owing to drilling and open air. For these reasons, the authors developed, by modifying the unsteady hot wire method, a field apparatus to measure local temperatures and thermal conductivities at seven points within one meter depth of perpendicular direction from soil surface in situ. The system consists of a prototype needle probe having 26 mm diameter and 1310 mm effective length, a constant power supplier, digital data recorders and a microcomputer system, etc. Consideration has been given to errors introduced by modification from the ordinary hot wire method theoretically and experimentally. The system proved to be able to measure the local thermal conductivvities of surface sod in situ with accuracy within ±8.5 % on the average for the values of the thermal conductivity from about 0.3 to 2.5 W/mK.
日本地熱学会の論文