## 2 High-Stress Appearance of Island Working Face
### Appearance of Dynamic Phenomenon  
Before a coal burst occurs, the coal pillar experiences a high energy state as a result of high static load; therefore, observation of the mine pressure in the field roadway can roughly judge the static load degree of the island working face at this time. Coal burst is the sound produced by the movement or destruction of coal rock. This means that the energy accumulated in the coal rock mass is released instantaneously.  
The field manual collection method was used to count the occurrence of dynamic phenomena such as roadway spalling, roof fall, floor heave, and coal burst during the excavation of the 5204-2 roadway (Figure 4). After eight months of continuous monitoring, the recorded data were collated and analyzed. The confirmation basis of the 'coal burst' event was that the rock surrounding the roadway emitted a similar'shotting' sound. The confirmation basis of the coal burst grade as'relatively strong' was based on the huge sound of the roof, accompanied by significant vibration, roof slurry peeling, and other phenomena, and the coal burst frequency of the coal burst phenomenon was more than 20 times. After continuous monitoring and data collation during the excavation period, the relationship between the dynamic phenomenon of the roadway and the width of the coal pillar during the excavation of the widened coal pillar area was obtained, as shown in Figure 5.  
Figure 4: Strong mine pressure behavior of 5204-2 roadway.  
Figure 5: Relationship between coal burst frequency and coal pillar width.  
The dynamic phenomena during the roadway excavation in the coal pillar widening zone had the following characteristics:  
(1) A total of 531 times of coal blasting occurred during the tunneling of the first coal pillar widening zone:  
8.2 m\(\sim\)33.5 m: The number of coal bursts was 10.44 times a day, and the number of relatively strong coal bursts was 2.69 times a day;  
3.6 m\(\sim\)7.9 m and 33.5 m\(\sim\)56 m: The number of coal bursts was 1.67 times a day, and the number of relatively strong coal bursts was 0.18 times a day;  
(2) A total of 2176 times of coal blasting occurred during the tunneling of the second coal pillar widening zone:  
22.4 m\(\sim\)64.4 m: The number of coal bursts was 19.54 times a day, and the number of relatively strong coal bursts was 4.38 times a day;  
47.9 m\(\sim\)50.6 m: The number of coal bursts was 8.72 times a day, and the number of relatively strong coal bursts was 1.89 times a day;  
68 m\(\sim\)64.4 m and 22.4 m\(\sim\)6 m: The number of coal bursts was 1.53 times a day, and no relatively strong coal burst occurred.  
In summary, it can be found that the dynamic phenomenon of mine pressure in the island working face is severe, and there are obvious high static load characteristics. In the first coal pillar widening zone, the phenomenon of coal burst mainly occurred in the range of 8.2 m-33.5 m during tunneling. In the second coal pillar widening zone, the phenomenon of coal burst was more frequent during tunneling. In different regions and ranges, there are noticeable variations in the frequency of coal bursts and the occurrence of relatively strong coal bursts. This suggests that the high static load on an island working face is related to the specific characteristics of each region.