Abstract: The transition from qualitative to quantitative analysis of rockbursts has been achieved, but assuming a completely failed medium within the ring-shaped softening zone is inconsistent with typical localized failure. We combined the StrataKing-3D parallel computing system for strata movement with the disturbance response instability theory of rockbursts, demonstrating broad applicability. However, only a simplified formula for the critical stress is adopted. For the common square tunnel in coal mines, effects of the type-Ⅱ fracture energy and internal frictional angle were investigated numerically, and the numerical critical stress was compared with the theoretical critical stress based on the complete formula. The ratio of numerical critical stress to theoretical critical stress was defined as a modification coefficient. For different type-Ⅱ fracture energies, the occupied region by the modification coefficient versus uniaxial compressive strength curves likes a trumpet, narrow on the left and wide on the right, indicating that a lower uniaxial compressive strength (or internal frictional angle) leads to the fact that the numerical result is closer to the theoretical result. The maximum numerical critical stress is less than 2.24 times the theoretical result. When the type-Ⅱ fracture energy is 200 N/m, the numerical result is closer to the theoretical result. For lower type-Ⅱ fracture energies (100–200 N/m), burst energy index ranges from 0.381 to 8.107, which largely falls within the survey data from 131 rockburst coal mines in China. Rockburst mines with burst energy index of 0–8 are the most prevalent. This suggests that the adopted type-Ⅱ fracture energy is appropriate. Under this condition, the numerical result is usually higher than the theoretical result. This can be explained through the viewpoint that the localized surrounding rock can possess a higher load-carrying capacity than the surrounding rock subjected to uniform failure. The difference between numerical and theoretical results is deepened in this study, laying a foundation for more accurate roadway safety assessment.

Key words: rockburst, roadway, critical stress, parallel computing, internal frictional angle, type-Ⅱ fracture energy, uniaxial compressive strength