Electrical response and dynamic monitoring of overburden failure in thin bedrock working face

Coal seam mining under thick unconsolidated layers and thin bedrock can lead to hydraulic connections between the working face and the overlying unconsolidated aquifer, potentially inducing water inrush and sand outburst disasters that severely threaten mine safety. Therefore, accurately characterizing the development of overburden failure is crucial. Using the 16041 working face in the Jiaozuo mining area of Henan Province as a case study, we combined numerical mining dynamics simulation, physical modeling with electrical similarity, and field monitoring to investigate the electrical response characteristics and dynamic monitoring techniques for overburden failure in thin-bedrock working faces. Both the numerical and physical modeling results clearly revealed the development patterns and typical electrical response characteristics of the caved zone and water-conducting fracture zone. During field monitoring, we utilized underground three-dimensional parallel electrical methods to determine the spatial distribution of bedrock thickness, which guided the layout of monitoring boreholes. We then applied a remote parallel electrical monitoring system to synchronously acquire both active and passive geo-electrical parameters. To overcome poor borehole formation and insufficient monitoring height near the bedrock interface, we developed a resistivity variation based dynamic imaging technique integrated with advanced detection. This method extended the effective monitoring height to 75 m, overcame the physical blind zone of the boreholes, and enabled cross-validation through full-space inversion. Field monitoring showed that the caving zone became compacted and stabilized during the mid-mining stage, with a measured height of approximately 18.5 m, terminating within the sandy mudstone above the No. 2₁ coal seam roof. The water-conducting fracture zone continued to propagate upward during the late mining stage, reaching a maximum height of 46 m, penetrating the entire thin bedrock layer and extending to the base of the Quaternary clay layer, potentially forming a direct water inrush pathway. The electrical response analysis indicates a distinct staged evolution during overburden failure: pre-mining damage caused an overall increase in apparent resistivity; the strong disturbance zone, corresponding to the caving zone, showed the largest resistivity variation and mid-term stability; the weak disturbance zone, corresponding to the water-conducting fracture zone, exhibited smaller resistivity variations but a clearly defined range and late-stage stabilization. These results are consistent with the staged overburden evolution characterized by mid-term compaction of the caving zone and late-stage upward expansion of the fracture zone. We developed an integrated monitoring approach combining pre-mining static detection, using three-dimensional electrical methods to determine bedrock thickness, with mid-mining dynamic monitoring, employing advanced borehole probing to extend beyond blind zones. This approach addresses the challenges of overburden failure monitoring in thin-bedrock working faces. Field application demonstrated that the method can accurately reveal the developmental height and spatial morphology of the caving zone and the water-conducting fracture zone, and support the assessment of potential water inrush risks, providing key technical guidance for water hazard prevention and safe mining in coal mines under similar hydrogeological conditions in East China.