Conductive textile electrodes for time-efficient ERT surveys performed in coarse-blocky mountain environments

Abstract

Electrical resistivity tomography (ERT) is one of the most accurate geophysical techniques to distinguish between frozen and unfrozen ground in permafrost areas. Performing the measurements, however, requires considerable logistics and time efforts. This is mainly due to the fact that optimal galvanic contact between the electrodes and the ground surface is necessary to collect reliable ERT datasets. Therefore, the traditional steel-spike electrodes must be steadily coupled between the boulders and wet with salt water on coarse blocky surfaces. To further decrease the contact resistances, sponges soaked in salt water can be inserted between the spike and the surface of rocks. Nevertheless, this traditional coupling system is particularly time-consuming, making it challenging to collect several ERT survey lines in a single workday in mountain environments. Recently developed conductive textile electrodes were applied to facilitate the deployment of ERT arrays in rock glacier environments. Instead of hammering the steel spikes, the conductive textile electrodes can be easily pushed between the boulders and wet with less water (compared to the sponges). Consequently, this new electrode approach decreases the time needed to prepare an ERT array. In this work, we evaluate the performance of the textile electrodes by comparing these with the traditional electrode approach, considering common investigation lines. This comparative test has been carried out in three test sites, which present different lithologies, surface characteristics and using different electrode spacing. The collected datasets were statistically analysed with robust regression analysis and Wilcoxon rank-sum test to examine the accuracy and significant differences between the two electrode systems regarding contact resistances, injected electrical current, measured apparent resistivities, reciprocal error, and inverted resistivity values. The obtained results demonstrate that conductive textile electrodes are suitable to collect reliable ERT datasets and, consequently, applying this approach in future ERT measurements performed in high mountain environments with coarse blocky surfaces (e.g. rockfall deposits, blocky slopes, or rock glaciers) would allow to acquire more survey lines (e.g. realisation of pseudo-3D geometries) extending the characterisation of the subsurface.