Borehole drilling in a coal seam is an efficient way to relieve ground stress and prevent coal burst. The deformational behavior and failure mechanism of a Φ50mm×L100mm coal sample with a 2–4 mm diameter drilling hole were studied under standard burst proneness laboratory testing. The results show that with the increase in borehole diameter, the uniaxial compressive strength (RC), impact energy index (KE), and elastic energy index (WET) decrease, and the dynamic failure time (DT) is prolonged. The overall burst proneness of the seam changes from strong to weak for a 4 mm hole sample. A high speed camera and acoustic emission (AE) monitor were used to study the deformation procedure and failure mode of the samples. It is found that cracks are propagated around the drilled hole at the initial stage of the loading, and the AE event and energy are weakened around the peak load. This suggests that the hole may significantly reduce the brittleness of the sample. The numerical method is employed to provide further insights on the internal deformation characteristics; the effect of hole sizes with diameters of 2–10 mm is also discussed. This paper provides quantified analysis methodology, monitoring technology, and borehole optimization for pressure relief drilling and burst proneness reduction in high coal burst-prone seams.

Entry retaining via roof cutting is a new longwall mining method that has emerged in recent years, and is characterized by high resource utilization and environmental friendliness. Due to the complexity of this method, a field study is commonly employed for process optimization. Roof blasting is a key operation for retaining the entry, and the current practice involves dynamically adjusting blasting parameters through on-site testing and postblasting monitoring. However, the existing literature lacks detailed descriptions of blasting operations, making it difficult for field engineers to replicate the results. In this study, based on a roof cutting project for entry retaining, a preliminary design of blasting parameters is made based on theories and on-site geological conditions. The on-site test methods and equipment for roof-cutting blasting are described in detail, and the fractural patterns under different blasting parameters are analyzed. After the retreat of the working face, the state of roof caving in the goaf is analyzed based on monitoring data, and the effectiveness of top cutting is evaluated through reverse analysis, leading to dynamic adjustments of the blasting parameters. This research provides a reproducible construction method for roof-cutting operations and establishes the relationship between blasting parameters and post-mining monitoring data. It contributes to the development of fundamental theories and systematic technical systems for entry retaining via roof cutting, offering high-quality case studies for similar geological engineering projects.

The recovery of top coal in the caving face directly impacts the efficiency of mining coal resources. The geological conditions and mining parameters are well known to be significant influences on the recovery of top coal. This study focused on the 9-301 working face, which is located in a thick coal seam with a large dip angle. The influences of the coal seam’s dip angle, mining direction, and coal caving mode and interval on the recovery were analyzed using PFC2D simulation. Field trials were also carried out. The results of the numerical calculations show that the recovery of top coal is clearly affected by the dip angle, with recovery decreasing as the dip angle is increased. Mining from the top to bottom along the dip of the coal seam is beneficial to improve recovery. The top-coal recovery using the multicycle-sequence coal caving method is higher than when using single-sequence coal caving and single-interval coal caving modes. The top-coal recovery using “one cutting and one caving” (coal caving interval of 0.8 m) was higher than that under two cuttings and one caving (coal caving interval of 1.6 m). During the field trials, the recovery of top coal under different caving intervals and modes was measured. The results show that the recovery of top coal is optimal when using one cutting and one caving with multicycle-sequence coal caving modes. The field measurements are consistent with the simulation results. The results of this study can help guide additional research for optimizing the recovery of top coal from thick coal seams with large dip angles.