Electrical resistivity tomography with combined arrays for shallow karst collapse hazard identification in Fuchuan, Guangxi, China

Shallow covered karst collapse is a prevalent geological hazard in Fuchuan County, Guangxi, China, posing severe threats to local engineering construction and human safety. To accurately identify subsurface karst structures and delineate collapse hazard zones, high-density electrical resistivity tomography (ERT) with Wenner, Schlumberger, and their combined array configurations was applied in a typical shallow karst hazard zone of Fuchuan. Field data were acquired with a 5 m electrode spacing for four parallel survey lines (ERT1–ERT4), and inversion was performed via the PyGIMLi software with a generalized Gauss–Newton method. The ERT results were validated against borehole data (BSWZK09) and single-pole resistivity depth curves. Quantitative analysis revealed that the Wenner array identified a broad low-resistivity karst anomaly (185–225 m along ERT1, 40 m lateral spread, 30 m depth, resistivity 50 Ω m) with superior vertical stratification resolution, while the Schlumberger array delineated a narrower, more defined anomaly (180–205 m along ERT1, 25 m lateral spread, 25 m depth, resistivity 40 Ω m) with enhanced lateral boundary recognition. The combined array integrated these advantages, achieving a vertical resolution of ±2.5 m and lateral resolution of ±3 m for karst anomalies. A total of eight karst collapse hazard zones and two regional underground karst development zones were delineated across the four survey lines, with ERT results showing 92% consistency with borehole verification data. This study demonstrates that the combined ERT array configuration effectively improves the detection accuracy of shallow karst structures in covered carbonate terrains, and the delineated hazard zones provide a critical geophysical basis for karst collapse prevention and engineering management in Fuchuan and similar karst areas.