Thermal Conductivity of Simulated Soils by the Needle Probe Method for Energy Foundation Applications

Soil thermal conductivity is an important parameter in the design of ground source heat pump and energy foundation systems. A laboratory method for measuring the soil thermal conductivity is the needle probe method. Earlier, analysis of the needle probe test data has been simplistic, relying heavily on human judgment and rules of thumb. This article presents an alternative method of analyzing the needle probe data with the aid of MATLAB, which is a technical programming language and computing environment. Four agar–kaolin specimens of varying densities were prepared to resemble simple soils. These were tested using the needle probe for a range of heating times and heating powers, to see what effect these parameters would have on the results. The repeatability when keeping the heating time and heating power constant was within ±2%. When the heating time and heating power were varied, the variation in results from the average for a given specimen ranged from ±4% to +10%/–8%. This range is significantly higher than the repeatability. Possible reasons for this are discussed in this article.