## 5 Analysis and Discussion of Numerical Simulation Results
### Analysis of Rockburst Risk Assessment for the Deep-Buried Roadway Crossing Stratigraphic Boundary
Figure 16 shows the results of the rockburst risk assessment in different formations after roadway excavation. According to the BSR index contour results, when the roadway crosses the C1d formation, the maximum BSR value reaches 0.50 at approximately 3 m from the arch top and arch bottom of the roadway, indicating a slight rockburst risk. The BSR value at the arch bottom is higher than at the arch top, implying a greater likelihood of rockburst in that location. This corresponds with site observations and worker descriptions in the 1104 section northeast of the vein near the 14# exploration line, where a slight rockburst  
Figure 16: Contour of BSR index distribution after completion of excavation. occurred: a brittle cracking sound was heard from the roadway roof, but no rock mass was ejected. When the roadway transitions from the C1d formation to the D3 zg formation, the BSR index peaks near the stratigraphic boundary (close to the D3 zg side), reaching a maximum value of 0.551, which also corresponds to a slight rockburst risk. Figure 17 shows rupture features observed in the rock mass near the stratigraphic boundary, which agree well with the numerical simulation results, indicating that the BSR index is a reliable predictor of rockburst risk. The likelihood of rockburst decreases as the roadway moves further away from the stratigraphic boundary within the D3 zg formation. Comparing the BSR index contour maps for the C1d and D3 zg formations, the larger BSR values in the harder D3 zg formation are concentrated closer to the excavation surface, whereas in the softer C1d formation, the higher BSR values are distributed further from the excavation surface. Based on the BSR index distribution, the rockburst risk in the D3 zg formation is more severe than that in the C1d formation, mainly due to the proximity of high-risk zones to the excavation surface. The rockburst risk assessment results provide guidance for field construction, allowing timely implementation of support measures at locations with elevated rockburst risk. Figure 18 shows a comparison of the roadway before and after the application of timely support measures. To evaluate the influence of different excavation directions on the rockburst risk of the surrounding rock, a geological model simulating excavation from the D3 zg formation (relatively hard rock) to the C1d formation (relatively soft rock) was constructed, based on possible field construction conditions, while keeping all other parameters identical to the previous model. The simulation results of the rockburst risk assessment for different excavation directions are shown in Figure 19. When the roadway is excavated from the D3 zg formation to the C1d formation, the maximum BSR index at the stratigraphic boundary reaches 0.619, indicating a moderate rockburst risk. Compared with excavation from  
Figure 17: Field geological structure and signs of rupture characteristics. the C\({}_{1}\)d formation to the D\({}_{3}\)zg formation, the zones with the highest rockburst risk in both scenarios are located near the stratigraphic boundary adjacent to the harder rock formation. Additionally, the rockburst risk is higher when excavating from harder rock into softer rock than in the reverse direction. Based on the combined results of numerical simulation and field observations, special attention should be given to evaluating the rockburst risk near stratigraphic boundaries when the excavation traverses formations with different lithologies. Corresponding rockburst prevention and control measures should be implemented when necessary during the construction process. Figure 19: Comparison of rockburst risk assessment results for surrounding rock in different excavation directions. Figure 18: Before and after support of the deep-buried roadway: (a) before support; (b) after support.