Modified Surface Electrodes with Bentonite Coupling for 2D Electrical Resistivity Tomography (ERT) on Interlocking Paving-Block Surfaces

Abstract

Electrical resistivity tomography (ERT) surveys on non-penetrable surfaces are challenging because conventional spike electrodes require direct ground penetration, limiting their use on interlocking paving-block surfaces. This study developed and field-tested a modified surface electrode (MSE) made of stainless steel, using bentonite clay as a coupling medium between the electrode and the paving-block surface. The MSE was compared with conventional spike electrodes using the Wenner-α configuration with an electrode spacing of 2.50 m under comparable acquisition conditions. A total of 84 Wenner-α measurements were acquired using 24 electrodes and subsequently subjected to quality control and two-dimensional resistivity inversion. The MSE produced an RMS error of 7.3% after seven iterations, compared with 5.7% after five iterations for the conventional spike electrodes. Both inversion models reproduced similar principal low- and high-resistivity patterns. The resistivity measurements showed a strong linear relationship, with a correlation coefficient of R=0.9368 and a coefficient of determination of R^2=0.8777. The results indicate that the MSE measurements followed a similar resistivity trend to the conventional spike-electrode measurements under the tested conditions. The MSE with bentonite coupling therefore shows potential for non-invasive ERT surveys on interlocking paving-block surfaces under the tested conditions, although further evaluation using quantitative agreement measures and different surface conditions is required.