# Research on Grading Evaluation of Coal and Gas Dynamic Disasters Based on Fuzzy Mathematics
## 4 Results and Discussion
#### 4.1.2 Determination of the Critical Values for the Wave Velocity and Abnormal Velocity Coefficient  
During the advancement of the 1010201-working face, the stress distribution around the working face was inferred based on the relationship between wave velocity and stress, allowing for the classification of stress concentration zones at different levels. The distributions of the longitudinal wave (P wave) velocity and abnormal velocity coefficient at different advancing distances (140.8 m, 151.1 m, and 161.4 m) are shown in Figures 9 and 10, respectively. Figure 8: Source distribution (>100 J) of 1010201-working face. The distribution of the longitudinal wave (P wave) velocity and abnormal velocity coefficient exhibit significant changes with the continuous mining of the 1010201-working face. At an advancement of 140.8 m, the high-stress concentration zone induced by mining disturbances is primarily located in the leading area C of the working face. The P wave velocity is classified into two levels: 5 m\(\cdot\)s\({}^{-1}\) and 6 m\(\cdot\)s\({}^{-1}\), while the velocity anomaly coefficient is categorized into three levels: 0.05, 0.15, and 0.25. At an advancement of 151.1 m, the high-stress concentration zones expand and are distributed across multiple areas, including the following:  
* The outer area A of the track roadway (P wave velocity: 5 m\(\cdot\)s\({}^{-1}\) and 6 m\(\cdot\)s\({}^{-1}\); velocity anomaly coefficient: 0.05, 0.15, and 0.25). * The inner corner area B of the track roadway (P wave velocity: 5 m\(\cdot\)s\({}^{-1}\) and 6 m\(\cdot\)s\({}^{-1}\); velocity anomaly coefficient: 0.05, 0.15, and 0.25). * The leading area C of the working face (P wave velocity: 5 m\(\cdot\)s\({}^{-1}\) and 6 m\(\cdot\)s\({}^{-1}\); velocity anomaly coefficient: 0.05, 0.15, and 0.25). * The outer area D of the belt roadway (P wave velocity: 5 m\(\cdot\)s\({}^{-1}\); velocity anomaly coefficient: 0.05 and 0.15). At an advancement of 161.4 m, the high-stress concentration zones remain prominent in several regions:
* The outer area A of the track roadway (P wave velocity: 5 m\(\cdot\)s\({}^{-1}\) and 6 m\(\cdot\)s\({}^{-1}\); velocity anomaly coefficient: 0.05, 0.15, and 0.25). Figure 10: Abnormal velocity coefficient distribution map of 1010201-working face: (**a**) advancing distance 140.8 m, (**b**) advancing distance 151.1 m, and (**c**) advancing distance 161.4 m.  
Figure 9: The longitudinal wave (P wave) velocity distribution map of the 1010201-working face: (**a**) advancing distance 140.8 m, (**b**) advancing distance 151.1 m, and (**c**) advancing distance 161.4 m.  
* The inner corner area B of the track roadway (P wave velocity: 5 m\(\cdot\)s\({}^{-1}\) and 6 m\(\cdot\)s\({}^{-1}\); velocity anomaly coefficient: 0.05, 0.15, and 0.25). * The leading area C of the working face (P wave velocity: 5 m\(\cdot\)s\({}^{-1}\); velocity anomaly coefficient: 0.05 and 0.15). * The inner goat area D of the belt roadway (P wave velocity: 5 m\(\cdot\)s\({}^{-1}\); velocity anomaly coefficient: 0.05 and 0.15). These observations indicate that the stress concentration zones dynamically evolve with mining progress, and the P wave velocity and the velocity anomaly coefficient can serve as critical indicators for assessing mining-induced stress variations in underground coal seams. The primary sources of uncertainty in the data acquisition process of the longitudinal wave (P wave) velocity and the velocity anomaly coefficient include variations in the accuracy and calibration of the microseismic monitoring sensors, which may introduce measurement deviations. Additionally, fluctuations in underground temperatures and humidity conditions can affect sensor performance. To reduce the impact of these uncertainties, instrument calibration and statistical corrections were applied during data collection, ensuring the reliability and accuracy of the acquired data.