Static-dynamic triggering mechanisms of rockburst in straight-walled arch roadways under different principal stress orientations and impact disturbances

This study investigates how principal-stress orientation affects impact disturbance triggered rockburst around straight-walled arch roadways. Coupled static-dynamic loading tests were conducted on specimens containing a straight-walled arch opening with orientation angles of 0°, 30°, 45°, 60°, and 90°, while principal-stress magnitudes and incident impact loading were kept unchanged. High-speed photography, digital image correlation (DIC), conformal mapping analysis, and dynamic finite-element calculations were integrated to examine failure evolution, strain localization, boundary stress redistribution, and final failure morphology. Results show that the rockburst process follows the typical progression from quiet stage through buckling-deformation and spalling-buckling failure to violent ejection. Failure-zone location, crack-propagation path, and particle-ejection direction vary markedly with stress orientation. As the principal-stress orientation increases from 0° to 90°, the left-side failure zone migrates from the straight-wall-arch-corner region toward the arch foot, whereas the right-side failure zone migrates from the circular-arch transition region toward the roof. Rockburst failure can be interpreted as the tension-dominated slab-spalling and buckling instability under concentrated tangential compression, with shear effects contributing to fracture coalescence. The static-dynamic triggering mechanism of rockburst is proposed in which static stress first localizes potential failure zones, impact disturbance activates these pre-localized zones, and stress-orientation-geometry coupled failure shaping controls the final crack path, ejection direction, and failure morphology.