An evaluation of two rapid methods of assessing the thermal resistivity of soil

The paper evaluates two methods recently proposed for the rapid assessment of the thermal resistivity of soil in situ, with special application to the assessment of cable ratings. Brief consideration is given to the factors determining the thermal resistivity of the soil, i.e. its composition, compactness and moisture content, and then to the present standard method of measurement by buried spherical or cylindrical heater. The basis of the so-called transient-needle method is then set out. Theory, errors due to departure from ideal conditions and practical application are considered. A method based on soil sampling is next discussed. After critical considerations of the underlying theoretical and practical work by Gemant, Kersten and Mickley in the United States, a nomogram is introduced by means of which the thermal resistivity of sand-clay mixtures of known physical characteristics may be simply determined. The practical application of the two rapid methods to field measurements is described, and results obtained by the various methods are compared. Finally, the new methods are discussed and compared with that using the static buried heater.