Application of a thermo-time domain reflectometry probe in sand-kaolin clay mixtures

Simultaneous measurements of soil thermal properties, moisture content and dry density are quite challenging, but very significant to geothermal related engineering applications. Thermo-time domain reflectometry (TDR) probe is able to measure soil thermal properties by the thermos probe, and predict soil moisture content and dry density by the TDR technique. This research studies the application of a new thermo-TDR probe in measuring thermal property, moisture content and dry density of sand-kaolin clay mixtures. Laboratory experiments were performed on five sand-kaolin clay mixtures with clay content ranging from 0% to 30% by dry weight. Measured thermal properties by the thermo-TDR probe were compared with a KD2 Pro. The moisture content and dry density were predicted by four alternative methods: Topp's equation, heat capacity method, one-step TDR method and Jung's method. The results revealed that Jung's method exhibited the highest prediction accuracy among the four methods, being the relative deviations between the predicted and measured values within 1% and 5% for gravimetric moisture content and dry density, respectively. It is concluded that the thermo-TDR probe can be applied in sand-kaolin clay mixtures successfully to accurately measure their thermal and geotechnical properties.