# Evaluation Method for Rock Burst Hazards in Strip Filling of Working Faces in Deep Coal Mines
## 4 Case Investigations
### Impact Hazard Evaluation
#### 4.2.2 Local Impact Risk  
From the mechanical mechanism of rock bursts, when the load of the coal body exceeds the limit of its bearing capacity, the coal body has the mechanical condition of impact instability. The impact tendency of the coal seam is the internal property of impact instability. In this section, the membership function of the stress state and the impact tendency of the coal body to rock bursts are proposed by using fuzzy mathematics. Before mining, the dangerous area of rock bursts is divided and classified, and the rock burst prevention design is carried out. During the mining of the working face, the evaluation results are verified by monitoring methods such as microseismic, stress, and drilling cuttings. According to the mining geological conditions of C8301 working face, the semi-quantitative analysis of self-weight stress, tectonic stress, and mining stress is carried out by using the multi-factor coupling calculation method of impact risk based on stress superposition, and the impact risk area of strip working face is divided and classified. 1. Vertical stress of mining roadway  
According to the cross-section diagram of belt entry and track entry of the C8301 working face, the elevation of the coal seam floor changes linearly with the mining direction. The surface elevation is +38 m. The intersection points of the belt entry, the track entry, and the open-off cut of the C8301 working face are taken as the origin of the coordinates. The \(x\)-axis is along the axis of the roadway, and the vertical stress is the \(y\)-axis. The rectangular Cartesian coordinate system for self-weight stress calculation is established as follows:  
\[\sigma_{\text{0-belt}}=20.2-0.005x\quad(0,\ 424) \tag{15}\]  
\[\sigma_{\text{0-track}}=19.45-0.0032x\quad(0,\ 424) \tag{16}\]  
The mining area of the C8301 working face is in a syncline structure. Under the action of the stress field, the syncline axis and two wings are the concentration areas of tectonic stress, and the top angle of the syncline structure is greater than \(110^{\circ}\). According to the previous analysis, the overlying strata movement of the filling mining face has an obvious time effect. The filling effect of the goat will affect the height and strength of the overlying strata movement, which leads to the obvious lag characteristics of the evolution time of the abutment pressure of the coal seam. The designed filling rate of the super-high-water material in the goat is not less than 80%. According to the roof structure, lithology, mining width, and mining conditions on both sides of the working face, the stress increment concentration coefficient of each influencing factor during the mining period of the working face is obtained as shown in Table 2, and the vertical stress calculation formula of the belt and track entry is obtained as follows. \[\sigma_{\text{all-belt}}= \begin{cases}22.22-0.0055x&(0,\ 60)\\ 24.24-0.006x&(60,\ 90)\\ 26.26-0.0075x&(90,\ 160)\\ 32.32-0.008x&(160,\ 300)\\ 36.36-0.009x&(300,\ 425)\\ \end{cases}  \tag{17}\]  
\[\sigma_{\text{all-track}}= \begin{cases}21.395-0.00352x&(0,\ 60)\\ 22.34-0.00384x&(60,\ 90)\\ 25.285-0.00416x&(90,\ 160)\\ 31.12-0.00512x&(160,\ 300)\\ 35.01-0.00576x&(300,\ 425)\\ \end{cases}  \tag{18}\]  
2. Impact risk area division  
According to Equations (2), (3), (17) and (18), the influence coefficient of the coal stress state on local impact risk is obtained as follows:  
\[\varphi_{\text{Lt-belt}}= \begin{cases}\frac{\sigma_{\text{all-belt}}}{2|\sigma _{\text{c}}|}-\frac{1}{2}&(0,160)\\ 1&(160,424)\\ \end{cases}  \tag{19}\]  
\[\varphi_{\text{Lt-track}}= \begin{cases}\frac{\sigma_{\text{all-track}}}{2| \sigma_{\text{c}}|}-\frac{1}{2}&(0,160)\\ 1&(160,424)\\ \end{cases}