A dynamic detection system was established by cross-inclined borehole electrical resistivity tomography (ERT), in order to monitor the water flow in Ordivician limestone (0LS) during development process of working face. The following approaches were adopted by the detection system. First, two inclined boreholes were constructed in the transportation roadway, and the metal joints of the cables were coupled to the surrounding rock of the boreholes by attaching the cables to metal sheets and grouting. Second, with a self-designed cable protection device, the cables were led out of the borehole to prevent the cables from being damaged by high-pressure grouting. Finally, supporting trenches were established in the transportation tunnel to prevent the cables from breaking down due to the falling of rock from the roof. During the development process of working face, data were acquired in five times. Combined with the distribution of the mine pressure and hydrogeological conditions, the abnormal areas with a low resistivity were accurately interpreted from the detection results, providing an early warning for the water inrush events from the floor.

To prevent the occurrence of water inrush from the working face floor, explorations of water-rich floors are necessary. For a working face with a regular shape, a water-rich floor can be detected by laying electrodes and cables around the working face. However, the rectangular working face develops an irregular shape, and the exploration of water in irregular working faces is a difficulty in the study of 3D electric resistivity tomography (ERT). In this paper, an unconventional dipole–dipole array is used for data acquisition and the potential of a non-grid point electrode is replaced by the potential of the surrounding electrode, which identifies a water-rich floor using 3D ERT with arbitrary electrode positions. Taking the 8826 irregular working face of the Baizhuang coal mine as an example, the working face is explored by 3D ERT, the anomalous area is delineated, and targeted grouting is carried out in the anomalous area. After grouting, the grouting effect is detected by 3D ERT, and the safe mining of the working face is ensured. The results show that grouting effect detection within the floor of a coal seam using 3D electric resistivity tomography (ERT) with arbitrary electrode positions could be applied to solving the problem of water-rich exploration of floors in irregular working faces.