Improving the galvanic contact resistance for geoelectrical measurements in debris areas: A case study

This paper aims to test, in a quantitative way, the different approaches that can be applied to improve the contact resistance problem in a debris environment for the acquisition of electrical resistivity tomography. We collected various datasets on the same investigation line in a blocky ground surface of a landslide deposit, using different coupling systems: single electrodes placed between the boulders, adding extra electrodes in parallel and drilled single electrodes inside the blocks. We performed the measurements in natural dry conditions, then we added salt water nearby the electrodes hammered among the boulders and we filled the drilled holes with a conductive carbomer-based gel. The results clearly demonstrate that using salt water significantly reduces the contact resistances, but also that, if salt water is not available, we can collect a good quality dataset in dry conditions by connecting more electrodes in parallel. Drilling the electrodes directly inside the boulders decreases the data quality but, if necessary, we demonstrate that the use of a commercial carbon polymer gel can provide a marked improvement in contact resistances.