Mechanisms and optimized blasting strategies for preventing bottom coal pressure relief failure in thick coal seam heading faces

To address the issue of bottom coal blasting pressure relief failure, the 1305-layer filling working face at Gucheng Coal Mine, Shandong Province, China, is selected as a case study. The investigation uses theoretical analysis, numerical simulation, field research, and on-site industrial experiments to understand failure mechanisms and propose an optimized blasting method. Findings indicate that post-blasting, the bottom coal divides into two zones: a bearing layer and a blasting and crushing zone. The bearing layer, more prone to energy accumulation, is critical to pressure relief failure due to an inadequate blasting scheme. The original scheme’s range is insufficient to reduce the bearing layer’s thickness below the critical threshold (CTFB). Theoretical calculations set the CTFB at 1.20 m, much less than the measured 3.50 m, confirming rockburst risks. Optimized blasting reduces pressure within the bottom coal by about 50%, decreasing the bearing layer's thickness from 3.39 m to 0.95 m, below the CTFB. On-site experiments confirm that this optimization effectively addresses bottom coal blasting pressure relief failure.