Significance  Mine direct current (DC) methods, an efficient geophysical exploration technique, can be used to identify and delineate underground electrical resistivity anomalies, serving as a critical means for the advance detection of water-bearing or hydraulically conductive structures ahead of the mining face.

Methods By combining the water exploration and discharge boreholes commonly used in coal mining and making reference to the observation system of the ground-based cross-borehole DC resistivity CT method, this study devised a dual-borehole DC resistivity observation system for advance detection. Through numerical simulation using the COMSOL software, this study constructed a homogeneous full-space model, in which a low-resistivity ball was used to represent a water-rich zone. Three types of observation configurations were developed, namely single-borehole sounding, dual-borehole profiling, and cross-borehole observation, with the included angle between a borehole and the tunneling direction set at 22.5°, 30°, and 45°. The full potential matrix was obtained through simulation, followed by apparent resistivity calculation and inversion imaging. Accordingly, the impacts of varying observation configurations and the included angles on the detection of the low-resistivity ball were compared.

Results and Conclusions In the case where the position of the anomaly was fixed, a larger included angle between a borehole and the tunneling direction corresponded to gentler apparent resistivity curves with less distinct extrema, making it difficult to identify the influence range of the low-resistivity ball. Conversely, a smaller included angle was associated with more pronounced local maximum and minimum values, suggesting more significant anomaly responses. The inversion results of numerical simulation show that a smaller induced angle corresponded to better alignment between the location of the low-resistivity anomaly and the actual position of the ball. Besides, it was also associated with greater consistency between resistivity and its preset values. Among various configurations, the cross-borehole observation yielded the highest detection performance. The inversion results from the physical simulation conducted using a water tank confirm that, as the induced angle decreased, the detection results of the observation configurations became gradually better in the order of single-borehole sounding, dual-borehole profiling, and cross-borehole observation with an increase in the size of data acquired. These findings are consistent with the results from the numerical simulation, further verifying the reliability of the proposed observation system. The results of this study provide new technical guidance for advance detection in roadway tunneling.