Spatial distribution and influencing factors of microseismic events in unequal-length mining faces in coal mines

Objective The varying length of a mining face along its dip direction or adjusting mining significantly increases water inrush risks of the mining face. This study investigate the hazards and influencing factors brought by unequal length arrangements to the mining face is one of the key issues in deepening the research on coal mine water hazard prevention and ensuring the safe mining face. Methods With the No. 15240 mining face, consisting of a narrow part, a wide part, and a slope, in the Jiulong Coal Mine of the Jizhong Energy Fengfeng Group as the engineering background, a large amount of microseismic monitoring data was analyzed. This study identified and visualized microseismic events using the STA/LTA model, obtaining multidimensional information such as frequency changes, planar distribution ranges, and vertical distribution characteristics. This data was then used to deeply analyze the microseismic events' activity and spatial distribution characteristics in various stages. Results and Conclusions Key findings are as follows: (1) The microseismic events exhibited pronounced staged spatio-temporal distribution characteristics during the mining of the unequal-length No. 15240 mining face. During the mining of the narrow part (i.e., the initial mining stage), microseisms were primarily distributed at the narrow part's edge close to the wide part. During the mining of the wide part (i.e., the middle stage), microseismic activity spread toward the interior of the wide part in the rear. From the mining of the slope, microseisms were concentrated at the turning parts of roadway and near geophysical anomalous zones. (2) In the narrow-to-wide transition zone of the mining face and mining adjustment zones, the activity and disturbance depths of microseismic events increased on the coal seam floors, establishing these zones as key areas for enhanced hydrogeological observations. (3) The stress redistribution caused by mining disturbance and the uplift of overlying coal seams, the pressure relief-induced instability of surrounding rocks in the roadway, and coupling effects of both served as the underlying causes of differences in the occurrence and distribution of microseismic events in various stages. This study revealed the general laws of microseismic activity caused by the mining of unequal-length mining faces, providing a new theoretical guide and data support for similar mining faces, including mining pressure monitoring, the assessment of damage depth to floors, and the dynamic warning of water hazards via microseismic monitoring. Accordingly, this study can provide important technical support for enhancing the safe production capacity of coal mines.