GNGTS 2021 - Atti del 39° Convegno Nazionale

GNGTS 2021 S essione 3.2 446 IMPROVING GALVANIC CONTACT RESISTANCE ON DEBRIS SLOPE: A COMPARATIVE TEST M. Pavoni 1 , A. Carrera 1 , J. Boaga 1 1 Department of Geosciences, University of Padova, Italy In the mountain eco-system, gravitational mass movement such as blocky landslides and debris flow are natural hazards with great socio-economic impact, causing infrastructures damages and even casualties (Petley, 2012; Papathoma-Köhle et al. 2015). In the context of in situ ground-based measurements, electrical resistivity tomography (ERT) method is widely used for the characterization and monitoring of landslide areas, e.g. to delineate depth and geometry of the sliding surfaces (Hack, 2000; Heinze et al., 2017; Boyd et al., 2019). However, high galvanic contact resistance between the electrodes and the ground can be problematic, decreasing the signal-to-noise ratio and consequentially affecting the quality of the acquired dataset (Binley, 2015). Anomalous or negative resistivity values recorded during the ERT measurements often highlight problems with contact resistances, a typical issue in all the high resistive environments, such as rocky ground surfaces of debris deposits or rock glaciers (Boaga et al., 2020). In our study case, we tested six different acquisition modes on the same investigation line in a heterogeneous rocky ground surface, the landslide deposits of “Marocche di Dro” (Province of Trento, Italy). We collected data with a Syscal Pro georesistivimeter (Iris Instruments), along an investigation line of 23 m with 24 stainless-steel electrodes (30 cm length), spaced 1 m apart and a Dipole-dipole skip-0 configuration. We acquired the datasets using different ways to ensure a good coupling and galvanic contact between the electrodes and the coarse-blocky terrain. Firstly, we performed the measurements by hammering the electrodes between the boulders (1 electrode in each position of the array - Fig 3A), subsequently we installed 2 extra electrodes connected in parallel to the main ones (a group of 3 connected electrodes in each position of the array for a total of 72 electrodes – Fig 3B), and finally we drilled the electrodes inside the boulders (1 electrode in each position of the array - Fig 3C). After the dry measurements, to decrease the contact resistances, we added salt water in the immediate vicinity of the electrodes placed between the boulders while, in the case of the drilled electrodes, we added a polymer based gel inside the holes. Fig. 1 - A) Single electrode placed between the boulders (1 per position); B) three electrodes in parallel placed between the boulders (3 per position); C) electrode drilled in the boulders with the hole (1 per position - here filled with carbomer-based gel).