# Evaluation Method for Rock Burst Hazards in Strip Filling of Working Faces in Deep Coal Mines
## 3 Impact Hazard Evaluation Method
### Impact Hazard Level Classification  
Based on the comprehensive index method, the impact hazard of the working face can be classified into four levels, which are no impact risk, weak impact risk, medium impact risk, and strong impact risk. The membership degree of the local and overall impact risks of the coal can be used [34]. The numerical range of [0, 1] is uniformly divided into four levels with an interval of 0.25, as shown in Table 1.  
According to the influence of coal seam stress state and impact tendency on the impact instability of the coal, the equations of local impact risk and overall impact risk index of filling working face are established as follows:  
\[U_{1}=w_{1}\varphi_{W_{\text{ET}}}+w_{2}\varphi_{L_{1}} \tag{12}\]  
\[U_{2}=w_{1}\varphi_{W_{\text{ET}}}+w_{3}\varphi_{L_{2}} \tag{13}\]  
where \(U_{1}\) is the index of local impact risk; \(U_{2}\) is the index of overall impact risk; \(w_{1}\) is the weight coefficient of the impact tendency of coal on the impact risk; \(w_{2}\) is the weight coefficient of the influence of the stress state of coal on the local impact risk, \(w_{1}+w_{2}=1\); and \(w_{3}\) is the weight coefficient of the influence of the stress state of coal on the overall impact risk, \(w_{1}+w_{3}=1\).  
According to engineering experience, the influence coefficients of coal stress state and impact tendency on impact risk are generally equal, which exists as \(w_{1}=w_{2}=w_{3}=0.5\)[35]. The weighting coefficients of each factor should be adjusted appropriately according to the actual geological and mining technical conditions. If there are one or more strong impact tendencies in the identification results of coal seam and roof/floor impact tendency, it indicates that the coal seam and roof/floor have a high capacity for accumulating elastic deformation energy and the possibility of local and overall impacts in the working face increases significantly. Therefore, the impact of the elastic energy index on impact risk should be increased. If the pending working face is located in the influence area of the remaining coal pillar in the same coal seam, the fault-cutting coal pillar or the coal pillar affected by the remaining coal pillar in the overlying coal seam, the basic static load borne by the working face coal is relatively large, and the stress increment threshold value for overall impact instability is lowered. Therefore, the influence coefficient of coal stress state on overall impact risk should be increased. If the working face includes areas with severe changes in dip angle, faults, connections, or proximity to the goat, the localized coal bodies  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Impact Hazard Level** & **Impact Risk Index \(U_{1}\)/\(U_{2}\) Values** \\ \hline No impact risk & [0, 0.25) \\ Weak impact risk & [0.25, 0.5) \\ Medium impact risk & [0.5, 0.75) \\ Strong impact risk & [0.75, 1] \\ \hline \hline \end{tabular}
\end{table}
Table 1: Impact hazard level classification of strip filling of working face.  
in these areas are prone to stress concentration, which can easily lead to high-stress-induced or high-stress gradient-induced impact instability. In this case, the influence coefficient of the coal stress state on local impact risk should be increased.  
When the impact risk index \(U\geq 1\), the impact risk is extremely high, and it is prohibited to mine that working face. When the impact risk index is \(0.5\leq U<1\), the impact risk is relatively high, and the working face can be mined after taking anti-impact measures. When the impact risk index \(U<0.5\), the impact risk is weak, indicating that the possibility of spontaneous impact is low.