Mechanism and effectiveness of regional strata modification via surface horizontal well fracturing for rockburst control in deep coal mines

In deep coal mining, massive and competent roof strata are a primary trigger of rockburst hazards due to their capacity to accumulate substantial elastic energy. At the 2803 working face of Hetaoyu Coal Mine (Ordos Basin, mining depth 954–989 m), multiple thick sandstone layers (> 10 m, UCS > 60 MPa) overlie seam No. 8, and elevated lateral abutment stresses inherited from the adjacent 2804 goaf create a compounded rockburst risk. To mitigate these hazards, a surface horizontal well (SHW) multi-stage hydraulic fracturing project was designed and implemented to target the Zhiluo Formation sandstone at a depth of 75–80 m above the coal seam. Fracturing was executed in 30 stages at 60 m spacing, with a per-stage fluid volume of 1,000–1,300 m³ and an injection rate of 8–12 m³/min. Surface microseismic arrays monitored fracture propagation in real time; underground microseismic monitoring and hydraulic support load cells characterised ground-pressure behaviour during the critical “square” (approximately 300 m advance) and “double-square” (approximately 470 m advance) stages. Microseismic inversion yielded a mean fracture half-length of 263.6 m and a mean height of 54.4 m, confirming effective stimulation of the target formation. Throughout the monitored mining period, no microseismic event exceeding 10⁴ J was recorded within the fractured zone. The microseismic energy per unit advance at the 2803 working face was 2.12 × 10⁴ J/m—a 75.2% reduction compared with the unfractured 2804 reference face (8.56 × 10⁴ J/m). Periodic roof caving intervals shortened to 9–16 m, and support resistance was predominantly maintained within 25–40 MPa. These results demonstrate that SHW multi-stage hydraulic fracturing effectively degrades the structural integrity of high-position competent roof strata, converting the energy release mode from impulsive rupture to progressive dissipation. The technique constitutes a viable regional pre-conditioning strategy for rockburst control in deep mines with analogous geological settings.