Development and Calibration of a Large-Scale Thermal Conductivity Probe

A large-scale probe has been developed for measuring the thermal conductivity of geomaterials. The large probe was designed to conduct tests on materials containing large particles, materials with high heterogeneity, and materials with high stiffness. The probe has dimensions of 680 mm length and 15.9 mm diameter and was constructed of stainless steel tubing. The probe operates on the principle of heating an infinite line source in an infinite medium. Initially, parametric evaluations were conducted to determine the operational and test conditions for the large probe, including power level, heating duration, and zone of heating influence. Then, tests were conducted on five homogeneous materials to calibrate the newly developed probe. Thermal conductivity measurements obtained using the large probe were compared with measurements obtained using a conventional small probe. A calibration curve was established for the large probe. In addition, the performance of the large probe was evaluated in two manufactured heterogeneous materials and a large particle material. The test program indicated that the large probe can be used effectively for determining thermal conductivity of geomaterials. This new probe may be suitable for large-scale laboratory testing and field investigations. Introduction Thermal conductivity of geomaterials needs to be known for analysis and evaluation of any engineering application involving heat transfer. Practical examples of thermal applications in geotechnical and geoenvironmental engineering include foundations for heated or cooled structures, buried high-power cables, underground space developments, various ground improvement applications, andwaste containment facilities. Thermal conductivity is needed for design that includes heat transfer applications as well as numerical analyses of heat transfer problems. The needle probe method is used commonly to determine thermal conductivity, based on the theory of an infinite line source of heat in an infinite medium. The currently available needle probe equipment and test procedures have limitations. The volume influenced by heating is small and the probe is fragile, which makes insertion of the probe into firm materials difficult. Improvements are required to broaden the applicability of the method to heterogeneous materials, materials containing large particles, and firm