Spatiotemporal response characteristics of transient electromagnetic field in water-bearing goaves and their applications

Objective and Methods This study aims to enhance the accuracy of the mine transient electromagnetic method (MTEM) in of imaging of water-bearing goaves. Based on the geological conditions of the Gaojialiang Coal Mine, this study simulated the spatiotemporal response characteristics of the induced magnetic field in the water-bearing goaf model under varying stratigraphic spacings using finite element software COMSOL. Accordingly, this study analyzed the distribution patterns of the induced magnetic field on the apparent resistivity pseudosections and the plots of the differentials of longitudinal apparent conductivity. Using the results, the water-bearing conditions of goaves in the Ordos Gaojialiang Coal Mine were successfully identified during field detection. Results and ConclusionsThe results indicate that the induced magnetic field in water-bearing bodies exhibited lower decay rates than that in rock layers. The time-varying voltage decay curves can be divided into four distinct stages: the initial stable, relatively slow, relatively rapid, and final stable decay stages sequentially. A greater stratigraphic spacing was associated with an earlier turning point between the initial stable and relatively slow decay stages, longer relatively slow and relatively rapid decay stages, and higher induced voltage. The maximum magnetic induction frequently occurred within the water-bearing goaves, decreasing linearly with an increase in the stratigraphic spacing. The second-order differentials of longitudinal apparent conductivity can effectively identify interfaces between high and low resistivity, with a smaller stratigraphic spacing corresponding to a higher amplitude of the second-order differentials. In the water detection of goaves along mining faces 20302 and 20313 in the Gaojialiang Coal Mine, the turning points of induced-voltage decay occurred at 718.51 μs and 1004.31 μs, respectively. The variations in the voltages between adjacent channels and the second-order differentials of longitudinal apparent conductivity reveal that water accumulation occurred at depths ranging from 36 to 120 m and from 24 to 168 m, respectively laterally and the rock-water interfaces were located at depths of 66 m and 72 m, respectively. These findings were verified through drilling. The results of this study can serve as a guide for water detection and drainage in goaves and hold great significance for ensuring the safe production of mines.