Evaluation of 2-D resistivity imaging technique for mapping and monitoring of subsurface cavity collapsed into sinkhole

Abstract

Geo-environmental hazard from near-surface cavities collapsed into sinkholes is alarmingly increasing in Northeastern Thailand. Detailed subsurface studies in the concerned areas are required for identification of sinkhole-prone areas, which may relieve fear of sinkhole hazard and help prevent possible and significant damage from the hazard. Thus, we examined the usefulness and capability of 2-D resistivity imaging technique for mapping and monitoring of surface cavities. We conducted 2-D resistivity survey at a man-made square tunnel, a known subsurface geology, and the nearby sinkhole areas. Synthetic resistivity data of various electrode configurations, including Wenner, Dipole-Dipole, Schlumberger, Pole-Pole, and Pole-Dipole were generated from the model similar to a known geology of the tunnel. We acquired a resistivity survey across the tunnel in a similar way to the synthetic data. Results from the field data show that the Dipole-Dipole and Wenner configurations provide better tunnel imaging. The tunnel appears as a lateral anomaly in a homogenous medium. An anomalous zone of the tunnel is distinguishable by the zone with high resistivity, surrounded by the lower background resistivity. However, location of the tunnel anomaly appears to be misplaced on the field resistivity pseudosection. It is different from the synthetic resistivity pseudosection. This suggests a strong 3-D effect from nearby structures. Results from the nearby sinkhole areas show that a Dipole-Dipole configuration provides a better result for cavity imaging than the Wenner configuration. An anomalous zone of the cavity is distinguished by very low and lowest resistivity zone surrounded by the higher background resistivity. These two results suggest that the 2-D resistivity surveys provide a reasonable basis for mapping a subsurface cavity. In addition, the 2-D resistivity survey was found to be useful for the monitoring of cavity progressive expansion, from similar resistivity survey was acquired at the same location when conducted at different times.