An investigation was conducted on the concealed karst and faults in the underground area of Zone C of the airport terminal building, in order to provide a basis for the subsequent design of the foundation of the site and the disposal of the adverse geological bodies.

The D+EM portable electromagnetic detection equipment integrates the time-domain D+TEM and frequency-domain D+FEM dual-mode detection technologies. By exciting the shallow geological body to generate a vortex field, it enables the identification of target bodies and the measurement of apparent resistivity. The equipment adopts a portable and lightweight design, with an exploration depth of 5 meters. When connected to a RTK base station, the planar positioning accuracy is ±1 cm, and the walking horizontal accuracy is 0.5 m.

A portable electromagnetic (EM) scanning system was deployed along ground-based survey lines spaced at 5-meter intervals. Each measurement unit was integrated with a GNSS receiver operating in network Real-Time Kinematic (RTK) mode to ensure centimeter-level positional accuracy for all survey points. Survey lines were traversed at a controlled speed of approximately 0.5 m/s. Both EM raw data and GNSS position records were acquired synchronously at a sampling frequency of 1 Hz. Survey points were extracted at 1-second intervals, and apparent resistivity values were computed for subsequent cross-sectional interpretation and comparative analysis.

All drill-identified karst cavities exhibit a consistent correspondence with zones of reduced apparent resistivity. Karst cavities originate from the dissolution of carbonate rocks by circulating groundwater, while highly fractured and fissured rock masses—also commonly saturated with groundwater—exhibit broader spatial distribution. Leveraging the well-established geoelectrical signature of dissolution-related fractures (i.e., low apparent resistivity), this survey delineated three-dimensional subsurface volumes with apparent resistivity values below 300 Ω·m as prospective dissolution-fracture development zones.

This investigation successfully characterized concealed karst features, fault structures, and other adverse geological conditions beneath Zone C of the airport terminal building. The resulting geotechnical dataset provides a scientifically grounded basis for foundation design optimization and risk-informed mitigation strategies targeting adverse geological units.