Research on the impact of borehole parameters on the instability and precursor characteristics of large diameter borehole in coal seam.

To examine the influence of borehole parameters on the instability and precursor characteristics of large-diameter boreholes in coal seams, this study conducts instability failure tests on coal samples with varying diameters, spacing, and row spacing. The investigation explores the effects of borehole parameters on the damage and failure of coal samples from the perspectives of stress distribution, crack propagation, failure modes, and acoustic emission characteristics. The following three points are addressed: (1) Increasing the borehole diameter and reducing the row spacing significantly enhances the pressure relief effect of large-diameter boreholes, necessitating rational adjustment of borehole spacing parameters for optimal performance. (2) The damage mechanism induced by borehole parameters primarily manifests as shear cracks, with minimal impact on tensile cracks. (3) A sudden decrease in the b-value indicates imminent rupture, and when the b-value reaches its minimum, the final failure of the coal sample occurs. The research findings enhance the understanding of the pressure relief process in large-diameter boreholes and provide a scientific basis for parameter selection and optimization in large-diameter borehole operations.