GNGTS 2013 - Atti del 32° Convegno Nazionale

within the whole central sector. The radial heat propagation is well described by the changes in electrical resistivity, showing an homogeneous radial distribution in the heat up. The more heterogeneously distributed resistivity during the cool down is probably influenced by some evaporation occurred within the medium throughout the test that could have influenced the propagation patterns. This can also partially explain the difference observed with temperature in the cool down period. The network configuration allowed us to describe the heat propagation in two dimensions around the source. The outcomes highlighted that the heat flows quite homogenously in a radial mode from the source, if no advective flux occurs. The possible differences within the medium, noted in particular in the cooling period, are caused by different water contents due to evaporation phenomenon which influences the local thermal properties. The electrical method was therefore useful to highlight heterogeneous water contents within the medium, key factor in the lab experiments performed for understanding the differences in the heat distribution at different saturation degrees (Comina et al. , 2013). Fig. 2 – Temperature and electrical resistivity differences plotted as a function of time. The lines and the dots show the temperature and resistivity trend respectively. The rounded numbers indicate the steps of the electrical measurements imaged in Fig. 3. Fig. 3 – Electrical resistivity difference map; plan view 10 cm. deep. The heat source is in the center and each step takes 2 hours. The upper row shows the heating period, while the lower row shows the cool down, after the source was turned off. The position of the heat source and the T-sensors are indicated. 126 GNGTS 2013 S essione 3.2