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Energies 2016, 9(10), 846;

Use of a Pre-Drilled Hole for Implementing Thermal Needle Probe Method for Soils and Rocks

Department of Civil and Environmental Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Korea
Norwegian Geotechnical Institute (NGI), Oslo N-0806, Norway
Power Transmission Laboratory, Korea Electric Power Research Institute, Daejeon 34056, Korea
Department of Civil Engineering, Inha University, Incheon 22212, Korea
Author to whom correspondence should be addressed.
Academic Editor: Kamel Hooman
Received: 19 July 2016 / Revised: 5 October 2016 / Accepted: 12 October 2016 / Published: 20 October 2016
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The thermal needle probe method, which is widely used for measuring the thermal conductivity λ of soils, deploys a long and thin metallic probe that houses a line heater and a temperature sensor. However, inserting such probes into consolidated or densely compacted soils or rocks is difficult, frequently causing buckling of the probe and severe disturbance to the surrounding ground, leading to unreliable measurements. We found that the use of a pre-drilled hole filled with thermally conductive grease for installing a thermal needle probe was feasible to overcome such challenges, and still yielded reliable measurements of thermal conductivity. The proposed method, i.e., the pre-drilling thermal needle probe method, was verified by finite element calculations and laboratory experiments by varying various parameters, such as the pre-drilled hole diameter, probe diameter, and thermal conductivity of thermal grease. It was observed that increases in the pre-drilled hole diameter and probe diameter and a decrease in the thermal conductivity of the thermal grease caused delays in temperature increase owing to the slowed heat transfer. Nevertheless, all the estimated λ values agreed well with the reference λ values with acceptable errors. Thus, the proposed method yields reliable measurements and can be applied for a wide range of soils from compacted soils to hard rocks. View Full-Text
Keywords: thermal conductivity; thermal needle probe method; pre-drilled hole thermal conductivity; thermal needle probe method; pre-drilled hole

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Lee, S.-J.; Choi, J.-C.; Baek, S.; Kwon, T.-H.; Ryu, H.-H.; Song, K.-I. Use of a Pre-Drilled Hole for Implementing Thermal Needle Probe Method for Soils and Rocks. Energies 2016, 9, 846.

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