Capacitively-Coupled vs. DC Resistivity Methods for Embankment Assessment: Achieving Equivalent Subsurface Characterization

다국어 초록 (Multilingual Abstract)

Capacitively-coupled resistivity (CCR) surveys offer a non-invasive alternative to conventional electrical resistivity tomography (ERT) for subsurface characterization in urbanized areas where electrode installation is impractical. However, the CCR method has an inherently lower signal-to-noise ratio than galvanic methods, and systematic data processing approaches to address this limitation have not been established. This study compares CCR and direct current (DC) resistivity surveys at the Gwangcheon Reservoir embankment in Chungcheongnam-do, Korea, to evaluate whether CCR can achieve equivalent subsurface characterization when appropriate noise removal procedures are applied. Five repeated CCR measurements were conducted along a 125 m survey line using the Ohm-Mapper TR-1 system, alongside two DC resistivity surveys using conventional multi-cable electrodes and a permanently installed Resistivity Measurement System (RMS). The apparent resistivity distribution of the CCR data ranged from 30 to 300 Ω·m, with values exceeding 300 Ω·m identified as noise. A noise removal threshold was determined by fitting a normal distribution to the apparent resistivity histogram. After noise removal, inversion results using ResIPy successfully detected all three characteristic low-resistivity zones of the reservoir embankment: (1) the boundary between foundation ground and fill layer, (2) the boundary between embankment edges and fill layer, and (3) the drainage tunnel periphery. These results were consistent with DC resistivity inversion results, which showed resistivity ranges of 50–150 Ω·m. Furthermore, statistical analysis of the five repeated CCR measurements demonstrated that the median function effectively derives representative apparent resistivity values, producing inversion results comparable to those obtained through explicit noise filtering. This study demonstrates that the CCR method achieves functionally equivalent subsurface characterization to galvanic DC resistivity methods when systematic noise removal or median-based data processing is applied, supporting its application for geotechnical investigations in paved urban environments.