# Mechanisms of Tunnel Rockburst Development Under Complex Geostress Conditions in Plateau Regions
## 5 Discussion  
For engineering disasters such as rockbursts, field investigations at construction sites provide an effective means to validate research conclusions. Due to limitations in data availability, a representative case study was selected for comparison. Field investigations conducted in a plateau tunnel revealed that the distribution of rockburst damage areas was generally consistent with the findings of this study.  
One such plateau railway tunnel is located in one of the most tectonically active regions in the world. Under strong tectonic influence, in situ measurements showed that the maximum horizontal principal stress reached up to 45 MPa, generally exceeding the vertical stress, with the ratio between them mostly ranging from 1.36 \(\pm\) 0.26. The tunnel has a maximum burial depth of 1696 m, and the surrounding rock mainly consists of granite and diorite. Tunnel construction primarily employed the TBM method, during which rockburst disasters frequently occurred. Based on the results of this study and the aforementioned conditions, it can be preliminarily inferred that rockburst disasters in this tunnel are likely concentrated around the crown and invert areas.  
Field observations confirmed a clear consistency in the locations of rockburst occurrences at different chainages, as shown in Figure 16. Within the currently excavated length of 5 km, bursting pits were mainly distributed from the crown extending towards both haunches and around the invert, while rockbursts were rare in other locations where the rock remained relatively intact. Photographs from points A, B, and C in a typical cross section are presented as examples of the rockburst areas and intact zones, respectively. The observed characteristics of rockburst disasters show significant correlation with the predicted spatial patterns from this study, demonstrating a high degree of consistency.  
Figure 16: Distribution and failure features of rockburst and intact zones in a plateau tunnel.  
The Qinghai-Xizang Plateau has a unique geological environment, with numerous factors influencing rockburst occurrence. In addition to significantly affecting the stress field, complex tectonic activity can create various tectonic geological bodies, such as fault zones and folds, which may lead to local stress concentration areas. When tunnels pass through these areas, the risk of rockbursts increases substantially. Moreover, complex tectonic activity may also result in regional geothermal activity [35], which can further influence rockburst occurrence.  
In addition to field validation, it is important to acknowledge the uncertainties and limitations inherent in the numerical modeling approach used in this study:  
1. Grid Size Sensitivity: Although a refined mesh was applied near the tunnel boundary, the overall mesh density may influence the resolution of stress concentration and energy accumulation zones. A finer mesh could better capture localized rockburst-prone areas, while coarser grids might smooth out critical gradients. Due to computational limitations, a formal mesh convergence analysis was not performed, which may introduce uncertainty in the accuracy of stress and energy distributions.
2. Assumption of Constant Rock Properties: The simulation assumes uniform granite properties, whereas natural rock masses often exhibit heterogeneity in strength, stiffness, and fracture density. These variations can alter local stress redistribution and energy release behavior, potentially affecting rockburst occurrence. This simplification may limit the model's representation of real-world complexity.
3. Uncertainty in Boundary Conditions: The applied boundary stresses were estimated based on empirical correlations, which may not fully represent actual in-situ conditions in tectonically active zones. Small deviations in initial stress assumptions could lead to significant changes in predicted risk zones.