Influence of Hydraulic Fracturing and Stress Unloading on Fracture Propagation in Deep Seam Excavation

Horizontal well drilling combined with hydraulic fracturing demonstrates significant potential in mitigating rockburst risks induced by overburden exposure during deep coal mining, yet the underlying stress-relief and anti-impact mechanisms remain inadequately characterized. This study employs the continuous–discontinuous element method to systematically investigate stress redistribution and impact resistance mechanisms within overburden structures following hydraulic fracturing in deep coal seams. A novel fluid–solid coupled multi-fracture modeling framework incorporating effective pillar width and fracture degree (FD) quantification enables comprehensive evaluation of fracture propagation patterns and structural weakening under varying geostress conditions and fracturing parameters. Key findings reveal: (1) Synergistic drilling-fracturing operations achieve 25.8% peak stress reduction through pillar width optimization, with post-injection stress relief reaching 27.12–42.16% in critical zones; (2) High geostress environments promote distinctive H-shaped fracture propagation, featuring vertical extension along bedding interfaces followed by lateral coal seam penetration; (3) Borehole 1 exhibits 23–37% lower FD than counterparts under extreme geostress, accompanied by pronounced brittle failure signatures. The established mechanical model provides critical theoretical foundations for optimizing hydraulic fracturing strategies in deep mining operations.