Electrical conductivity versus temperature in freezing conditions: a field experiment using a basket geothermal heat exchanger

In-situ experiment. Geothermal setup: Five heat exchangers (HE) are arranged in a line and are buried between 1.1 and 3.5 meters. Just two baskets worked: one (HE.5) for a correct functioning of the heat pump and the other (HE1) to freeze the ground. only, this last exchanger (HE1) has been monitored in temperature and electrical resistivity tomography. The basket HE.5 is too far away to have an influence during this experiment, the heat pump was started at 0 hour and worked during 518 hours. The temperature of ground was recorded every minutes, thanks to 41 probes (4 wire Pt100), divided into 7 vertical profils. theses profiles are located at 0, 3, 6, 7, 8, 11, 20, 21 meters (x-distance), and the used heat exchangers are at 7 meters for the HE.1 and at 24 meters for the HE.5, respectively. Electrical Resitivity Tomography (ERT): Before and during the running of the geothermal system, gephysical monitoring was carried out. At the end, nine tomography images were recorded using a SAS-100...