## 5 Quantitative Assessment of Roadway Rock Burst Risk  
### Discrimination Parameters for Roadway Rock Burst Risk  
In practical tunneling operations, monitoring the difference between maximum and minimum principal stresses, as well as changes in horizontal stress, facilitates the implemen  
Figure 7: Plots of coal mass kinetic energy versus time steps under different ground stresses.  
tation of effective preventive and control measures against rock burst. Three parameters can be employed for quantitative evaluation. The parameter \(D_{g}\) illustrates the stress difference gradient of coal mass, and \(D_{g1}\) means the \(D_{g}\) value of coal mass at a depth of 1 m within the roadway side, and the change rate of the stress difference gradient can be expressed as \(D_{gc}\), which can be calculated from \(D_{g}\) and \(D_{g1}\)[11].To investigate the influence of mechanical properties on coal mass burst during tunneling, the \(D_{g1}\) at the roadway sides is compared with D\({}_{g}\) in the elastic-plastic boundary region of the roadway under varied parameters.  
From engineering experience and case studies of rock burst accidents, the critical condition for rock burst occurrence is \(D_{gc}\geq[D_{gc}]\), where \([D_{gc}]\) is semi-quantitatively calculated. Considering the simulated elevated zone depth of the roadway (\(D_{gmax}\)) and the influence of the coal seam parameters on \([D_{gc}]\), a specific value of 13 is established for \([D_{gc}]\) in this paper.  
Figure 8 depicts the gradient of the three-way stress difference with respect to the number of time steps during roadway tunneling under different ground stress environments. It can be observed that the gradient rate of change of the three-way stress approaches critical levels for rock burst damage under a vertical stress of 30 MPa (at a burial depth of approximately 1100 m). Moreover, the rate of change in this gradient is linearly correlated with stress levels. This suggests that rupture surfaces in coal-and-rock mass in deep mining parallel to the maximum principal stress direction can be generated through controlled blasting, with accumulated energy released, thereby preemptively reducing the likelihood of rock burst damage.  
As depicted in Figure 9, several groups denoted as b-e and h, show \(D_{gc}\) values significantly higher than the critical threshold, and dynamic rock burst damage can occur. Conversely, the remaining groups have \(D_{gc}\) values below the critical condition, indicating a proximately static failure rather than rock burst damage.  
Figure 8: Histogram of three-way difference gradient and rate of change for coal mass under different ground stresses.  
It can be noted form Figures 5, 6 and 9 that the analysis of \(D_{gc}\) under different coal mass parameters is correlated with changes in the kinetic energy and displacement curves. For instance, although Group j shows a displacement curve similar to the groups with burst damage, its kinetic energy change is more aligned with the groups with static failure. For Group h, the \(D_{gc}\) value surpasses the critical condition despite the peak kinetic energy being significantly lower than in other groups with burst damage. Therefore, its energy dissipation and coal rock motion characteristics still satisfy the rock burst occurrence criteria.  
Therefore, the stress difference gradient can be a powerful factor in predicting and mitigating coal and rock mass burst hazard within roadway sides, which could provide guidance for roadway stability evaluations under varied geotechnical conditions.