# Evaluation Method for Rock Burst Hazards in Strip Filling of Working Faces in Deep Coal Mines
## 2 Impact Hazard Identification Criteria  
The total stress of the strip filling of working faces after superimposed static stress and dynamic stress was compared with the strength of the coal body. At the same time, according to the third chapter of the \"Detailed Rules for Prevention and Control of Coal Mine Rock Burst\" issued by China National Mine Safety Administration, the impact risk is divided into four categories: no impact risk, weak impact risk, medium impact risk, and strong impact risk according to the ratio [25]. The relationship between the filling rate and the impact risk of the strip filling of the working face was obtained, as shown in Figure 1.  
The concept of a critical filling rate was proposed. When the strip of working faces adopts filling mining, the filling rate determines the movement characteristics of the overlying rock in the goaf and its dynamic loading effect on the coal body. The greater the filling rate, the weaker the dynamic loading effect of overlying rock movement, and the smaller the total stress of the coal body in the strip working face, indicating a negative correlation between the total stress and the filling rate. When the total stress is less than the impact risk line, this filling rate is the critical filling rate for the corresponding impact hazard level. In Figure 1, the critical filling rate is the filling rate when the total stress curve intersects with the weak impact risk line, medium impact risk line, or strong impact risk line, according to the relevant engineering experience and field monitoring results. The five curves represent the relationship between filling rate and impact risk under five mining geological conditions, respectively. This is specifically expressed as follows:  
* Filling rate \(\eta_{i}=0\) represents the working face being unfilled, i.e., using the caving method to manage the goaf roof. If the total stress of the working face is lower than the weak impact risk line, it indicates that the overall level of the support pressure of  
Figure 1: Relationship between the filling rate and the impact risk of the strip filling of working face: 1—using the caving method to manage the goaf roof; 2, 3, 4—using filling mining method to manage the roof of goaf; and 5—using caving method or filling mining method to manage the roof of goaf.  
the strip working face is lower than the minimum stress value that induces impact, and the strip working face has no impact risk. At this time, although filling mining can slow down the dynamic pressure manifestation of the coal body in front of the working face, it has no essential impact on the hazard level of the strip working face, as shown in curve 1 in Figure 1.
* For strip working faces with a medium or higher hazard level using the caving method, filling mining can significantly reduce the impact risk of the working face, as shown in curves 2, 3, and 4 in Figure 1. When the filling rate \(\eta_{\ell}\) increases, the intensity and range of fracture motion of low-level rock beams decrease, resulting in a decrease in dynamic stress and a decrease in the impact risk. There are one or more critical filling rates. When the filling rate is greater than the critical filling rate, the impact risk is reduced to weak or below. This indicates that filling mining effectively reduces the impact risk in strip working faces. When the filling rate is less than the critical filling rate, the total stress is still greater than the critical stress for impact to occur. The impact risk after filling is still moderate or above. This indicates that the use of filling mining as a single measure cannot effectively eliminate the impact risk. In this case, other anti-impact measures should also be carried out.
* Curve 5 in Figure 1 indicates that regardless of filling or not, the impact risk of the strip working face is always strong. The possibility of a rock burst is extremely high, which indicates the working face is unsafe and unable to be worked upon.