Mechanisms of rock burst instability in deep coal roadway with high three-way stress difference area

Addressing the issue of rock bursts and instability in deep coal roadways with high three-way stress differences，this study employs theoretical analysis，numerical simulations，and engineering case studies to reveal the mechanisms of rock bursts and instability in such areas. Based on the Mohr-Coulomb criterion，the definition of the three-way stress difference is modified to Δ<italic>σ</italic>=<italic>σ</italic>₁-<italic>σ</italic>₃（1+sin<italic>φ</italic>）/(1-sin<italic>φ</italic>)，providing a quantitative damage criterion for coal body units. High three-way stress differences in deep coal mines are categorized into horizontal tectonic stress type and vertical stress type based on their origins. After roadway excavation in high-stress difference areas，the coal rib experiences significant crack development and increased damage extent. Additionally，there are higher movement speeds，larger displacements，and faster destruction rates. The peak value of the three-way stress difference，distributed radially around the surrounding rock，defines the interface between the failure and non-failure zones. The failure zone suppresses the increase in three-way stress difference in the non-failure zone，while the three-way stress difference distribution in the non-failure zone plays a dominant role in controlling the stability of the coal roadway. A stability parameter，<italic>S</italic>_s，is proposed to describe the stability of the surrounding rock of coal roadways or in unexcavated coal configuration areas. When the surrounding rock's <italic>S</italic>_s is less than the critical [<italic>S</italic>_s] of the non-failure zone boundary，accumulated deformation in the non-failure zone drives coal from the failure zone towards the roadway，leading to instability. When <italic>S</italic>_s decreases sharply，the non-failure zone rapidly fails，and significant deformation accumulation drives the coal body in the failure zone to experience a rock burst. This mechanism is validated through a case study of a rock burst incident in the high three-way stress area formed by a coal pillar at the Huafeng coal mine.