Background  The redevelopment and reutilization of closed/abandoned mines hold great research significance and practical production value due to their substantial number. In China, the secondary development and utilization of energy and spatial resources in such mines started late, rendering foundational theories and key technologies relatively underdeveloped.

Methods To investigate the developmental characteristics of underground spaces within goaves in closed/abandoned mines, this study proposed a reflected radio wave-based exploration method. Specifically, an observation system with a fixed transmitter-receiver (TR) spacing was deployed in rock roadways above/below or on both sides of the mining face in a closed/abandoned mine. Then, a 3D layered geoelectric numerical model was established to simulate and analyze the responses of reflected radio waves for goaves with homogeneous media and those with water- or gas-bearing anomalous structures under multiple frequencies and TR spacings.

Results and Conclusions Numerical simulation results indicate that the reflected radio waves of a homogeneous medium in a goal showed linear wave fields. In contrast, water-bearing and gas-bearing anomalous structures in a goaf attenuated and amplified reflected radio wave signals, respectively, corresponding to concave and convex curves of received wave field strength, respectively. Physical simulation experiments using similar materials conducted on a subaqueous tunnel yielded results with five distinct segments. The results are consistent with the actual geological conditions of the tunnel, verifying the effectiveness of the proposed method. In combination with existing experience, this study carried out reflected radio wave-based exploration experiments on a mining face of a closed/abandoned mine and obtained data. The experiment results accurately presented potential geological anomalies in the anomalous areas of the No. 9 coal seam. These results are consistent with the mining survey data and drilling results, suggesting encouraging application effects. This study verifies that it is feasible to detect goaves in coal mines, along with anomalies within the goaves, using the proposed reflected radio wave-based exploration method, offering a new approach for underground space exploration in closed/abandoned mines.