Objective In recent years, floor water inrushes have frequently occurred in North China-type coalfields. To address this challenge, determining the anomalous responses of water inrushes from stope floors has emerged as a focus of research on water disaster prevention and control.
Methods This study established a stress model of the stope floor based on the mine pressure theory. Using this model, it analyzed the stress distribution and failure characteristics of the stope floor. The floor failure characteristics revealed that the coal seam floor can be divided into three zones: the compression, expansion, and recovery zones. Through stress-resistivity tests, this study investigated the resistivity variation patterns of rock samples under the loading, failure, and recovery states and simulated the resistivity variations in the compression, expansion, and recovery zones in the mining face floor, thus determining the resistivity in the three zones. In combination with the resistivity variations of field strata, this study established a dynamic 3D geoelectric model to examine the spatiotemporal evolution of the floor resistivity during different mining stages. Using procedures of the 3D direct current electric method, this study conducted forward modeling and inversion using the geoelectric model and prepared 3D resistivity plots of the anomalous responses from the mining face floor. Accordingly, this study investigated the anomalous responses from the mining face floor and summarized the anomalous response characteristics during the mining face advancement.
Results As the mining face advanced for 20 m, a stress anomaly zone and a low-resistivity anomaly zone appeared in the geoelectric model. The stress anomaly zone appeared in front of the mining position of the working face. It primarily influenced shallow strata, disappearing with increasing depth. In contrast, the low-resistivity anomaly zone primarily affected deep strata while producing no impact on shallow strata. When the mining face advanced for 30 m, the stress anomaly zone moved forward as well. Consequently, the stress anomaly zone was connected to the low-resistivity anomaly zone, accompanied by the continuous expansion of the low-resistivity anomaly zone and a constant decrease in the apparent resistivity. As a result, significantly low resistivity anomalous responses occurred, indicating an increased possibility of water inrushes from the mining face floor. When the mining face advanced for 50 m, two low-resistivity anomaly zones were observed along the mining face. Among these, one was identified as a stress-induced low-resistivity anomaly zone, moving forward as the mining face advanced. Another low-resistivity zone was found in the goaf. This area was characterized by a large range and extremely low apparent resistivity, which differed significantly from that of the surrounding rocks. This suggests an extremely high possibility of water inrushes from the mining face floor.
Conclusions During the advancement of the mining face, the characteristics of stress and low-resistivity anomalous responses can be observed. Among them, the stress anomalous responses show a limited influence range, keeping moving forward as the mining face advances. In contrast, low-resistivity anomalous responses exhibit a wide influence range and a significantly different apparent resistivity from the surrounding rocks. These responses keep expanding as the mining face advances. Prevention and control measures should be taken in time to prevent water inrushes from the mining face floor.
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