Mechanism of rock burst in deep coal tunnel surroundings due to three-way stress difference gradient

With the deep coal tunnel surrounding rock as the research object, in view of the serious rock burst hazards, incomplete rock burst mechanism research, and the lack of more targeted guidance on the prevention and control of rock burst engineering, indoor tests, numerical simulation, theoretical analysis and other methods were used to reveal the deep coal roadway surrounding rock burst mechanism from the three-way stress difference perspective. Based on the understanding that excavation activity disturbs the three-way isobaric state of the coal rock body and causes damage to the surrounding rock, the response characteristics of the coal unit body under the action of different stress paths were studied by PFC simulation. The criterion of unit body instability based on the stress difference was obtained. The concepts of stress difference gradient and the rate of change of stress difference gradient were proposed. The D_g evolution characteristics of the surrounding rock were analyzed based on the Drucker-Prager criterion, and then the mechanism of action of the rock burst caused by the concentration of D_g in the surrounding rock was obtained. Finally, the prevention and control mechanism and rock burst accident cases were analyzed. The results show that the stress differential withstand capacity of the coal body differs significantly depending on the stress path. The objective of the evolution of the internal stresses in the surrounding rock is to reduce the peak D_g to a very small value, with the failure and yielding of the surrounding rock being the result of D_g-driven action. The stress difference gradient grows with the increasing depth of burial and coal seam bursting liability, and reflects the nature of the “rise-fall-fall” gradient. The D_gc characterizes the degree of D_g concentration within the surrounding rock. Under stress perturbation, a more stable deformation and displacement of the coal body in the D_g elevation zone occurs when the condition D_gc0 < D' _gc < k₁D_gc0 is satisfied, a more stable overall instability occurs when k₁D_gc0≤D' _gc < D_gc is satisfied, and a rock burst occurs when D' _gc≥D_gc is satisfied. Rock burst of the surrounding rock is an extreme form of evolution of their own deformation and destruction. Rock burst prevention should be centered on weakening the D_g of the surrounding rock, with D_gc control as the main focus.