Validation of a Thermo-Time Domain Reflectometry Probe for Sand Thermal Conductivity Measurement in Drainage and Drying Processes

The thermo-time domain reflectometry (TDR) probe is a promising tool for simultaneous measurements of the thermal and geotechnical properties of soil under both laboratory and field conditions for geothermal applications. This study presents the validation of a thermo-TDR probe for sand thermal conductivity measurement during drainage and drying processes. Laboratory experiments were performed on four quartz sands with different particle sizes using a modified hanging column device. A KD2 Standard Pro was used to measure sand thermal conductivity, which was then compared with the results obtained by the thermo-TDR probe. A series of statistical analyses, including root mean square error, mean absolute error, and variance account for, was conducted to further evaluate the performance of the thermo-TDR probe for sand thermal conductivity measurement during the dryout process. It was concluded that the thermo-TDR probe can measure sand thermal conductivity accurately with at least 85 % confidence interval during the drainage and drying processes. The measurement accuracy of the probe increases as the grain size of the sand decreases.