Sidewall-Based Three-Dimensional DC Resistivity Imaging for Identifying Potentially Water-Bearing Zones Around an Operational Railway Tunnel

Abstract

Groundwater ingress and moisture-related deterioration threaten railway tunnels in fractured and hydrogeologically active terrains. This study evaluates sidewall-based three-dimensional (3D) direct current resistivity (DCR) imaging for investigating potentially water-bearing conductive zones around an operational railway tunnel in Sivas, Türkiye, where crown measurements were operationally impractical. Field data were acquired along three profiles on opposing tunnel sidewalls and inverted using an unstructured tetrahedral mesh representing the tunnel cavity and acquisition geometry. The field model revealed low-resistivity zones adjacent to both sidewalls, with some features extending towards and above the crown. A field-informed synthetic reference model was used to assess survey-dependent recoverability rather than independent validation. The sidewall configuration recovered the principal conductive structures and their upward continuity, whereas longer parallel surface profiles recovered them more broadly and less distinctly. LiDAR intensity variations and field-observed wet areas provided complementary qualitative indications of surface moisture. Overall, sidewall-based 3D DCR imaging, combined with sensitivity and field-informed recoverability assessment, provides a practical strategy for operational tunnels where circumferential measurements or intrusive verification are difficult.