GNGTS 2013 - Atti del 32° Convegno Nazionale

Additionally, the thermal properties of the medium can be achieved by means of the electrical surveys results. Applying Eq. (3), we obtained the thermal resistivities of the medium at each of the 19 steps, starting from the recorded electrical resistivities. We calculated the multiplier C R with the equations proposed by Sreedeep et al. (2005), founding a value of C R = 2.01. The results, ρT ranging between 6.56 and 4.56 °C m W -1 , are reported in Tab. 1. The outcomes are rather high for a fine sand but in general accordance with many studies on this topic (Sreedeep et al. , 2005; Singh and Konchenapalli, 2000). Tab. 1 – Thermal resistivities close to sensors t1 and t3, calculated with Eq. (3). sensor t1 sensor t3 steps ρE temperature ρT ρE temperature ρT [Ω m] [°C] [°C m W -1 ] [Ω m] [°C] [°C m W -1 ] 0 33.96 19.40 5.54 48.16 19.40 6.56 1 28.98 22.70 5.13 38.39 27.80 5.88 2 26.85 28.90 4.94 35.06 37.20 5.62 3 25.78 33.30 4.84 33.82 41.70 5.53 4 25.05 35.50 4.78 33.11 43.90 5.47 5 24.48 37.20 4.72 32.59 45.60 5.43 6 23.97 38.90 4.68 32.08 47.20 5.39 7 23.49 40.50 4.63 31.52 48.30 5.34 8 23.12 41.10 4.59 31.09 49.40 5.31 9 22.81 42.20 4.56 30.71 50.00 5.27 10 23.29 41.10 4.61 31.83 46.10 5.37 11 24.14 37.70 4.69 33.65 40.00 5.51 12 24.71 35.00 4.75 34.86 36.70 5.61 13 25.17 32.70 4.79 35.83 33.90 5.68 14 25.54 31.10 4.82 36.59 32.20 5.74 15 25.84 30.00 4.85 37.25 30.60 5.79 16 26.13 28.90 4.88 37.83 29.40 5.84 17 26.35 27.70 4.90 38.35 28.30 5.87 18 26.56 27.20 4.92 38.79 27.20 5.91 19 26.73 26.10 4.93 39.20 26.70 5.94 Conclusions. The first experimental results of this study confirmed the expected correlation of decreasing electrical resistivity with an increasing temperature induced by the heat source. A general negative variation of around 2.5% of resistivity was recorded when a temperature increase of 10% occurs. Moreover, the correlation between electrical and thermal resistivities was tested. Our electrical surveys on the lab device highlighted therefore their potential for monitoring and quantifying the increase in temperature at the respective measuring points and the differences in heat propagation through the medium. A possible future work that could be carried out includes further testing of different materials under the same conditions, to ensure comparability of the different media and their influencing soil parameters for the thermal and electrical conductivities. 127 GNGTS 2013 S essione 3.2