New thermal cell for measuring thermal conductivity of soils

Abstract

The purpose of the present work is to develop a cost-effective, simple, and robust laboratory apparatus for determining the thermal properties of soils.2 THERMAL CELL APPARATUS AND TEST PROCEDUREThe function of the thermal cell apparatus is to characterize the thermal properties of soil. Several past and current experimental devices were studied and taken into consideration during the design of the new soil specific thermal conductivity cell. The most important requirement in designing1 INTRODUCTIONHeat transfer through soils and geomaterials is encountered in engineering fields such as energy piles, thermal ground improvement techniques, waste containment facilities, and underground power cables (Thomas & Sansom 1995; Yesiller, Hanson, & Liu 2005; Brandl 2006; Abuel-Naga, Bergado, & Chaiprakaikeow 2006; Laloui, Nuth, & Vulliet 2006). No standard laboratory tests to measure thermal conductivity of soils have been identified, though a number of tests exist for the measurement of thermal conductivity of building materials. Tests include the comparative method (ASTM 1997c), the guarded hot plate method (ASTM 1997b), the hot wire method (ASTM 1997a), the thermal needle test (ASTM 1997d) and the unguarded hot plate method described in the (BS 1988). Experimental methods of measuring thermal conductivity can be steady state methods or transient state methods. The guarded hot plate method (GHP), the hot wire and probe methods are the most accepted in industry for soil thermal conductivity measurements. The GHP method is generally regarded as accurate. However, it is usually quite time consuming. The hot wire and the probe methods require much less time. The GHP method, and other methods that use the principle of the longitudinal heat flow at steady state condition were developed for structural and insulation materials and have limited applications for soils. The test of the apparatus for these methods require large specimen sizes, which are difficult to obtainthe new thermal conductivity cell is to use soil samples obtained in routine site investigations. This requirement limits the size of the specimen to the tested to 103 mm diameter.