## 4 Stress Distribution Law in Island Working Face
### Numerical Simulation Results Analysis
#### 4.2.4 The Stress Distribution Influenced by Coal Seam Thickness  
The stress distribution features of the island working face were simulated under different coal seam thickness conditions, as shown in Figure 14(a). The simulation results indicate that with the increase of coal seam thickness, the plastic zone of the roadway surrounding the rock and coal pillars in the island working face shows a trend of gradual expansion. When the thickness of the coal seam reaches 8 m, the stress distribution of the coal pillar shows a unique bimodal feature, and the stress peaks on both sides are 27.6 Mpa and 33.1 Mpa, respectively. Figure 14(b) shows the variation law of the coal pillar stress and the evolution characteristics of the plastic zone under different coal seam thickness conditions. The simulation results indicate that when the coal seam thickness is 8 m, 12 m, 16 m, and 20 m, the total proportion of the number of coal pillar plastic zone proportions is 36.25%, 44.72%, 56.25%, and 67.67%, respectively, and the corresponding peak stress is 33.1 Mpa, 35.3 Mpa, 33.5 Mpa, and 31.2 Mpa, respectively. Under the condition of an 8 m thick coal seam, a significant elastic core is formed in the center of the coal pillar, which is the embodiment of the strongest bearing capacity of the coal pillar. Therefore, the stress distribution of the coal pillar in this state shows a clear bimodal characteristic, rather than simply showing the level of the stress peak. In fact, due to the existence of an elastic core, the stress distribution of the coal pillar is more uniform and stable. However, with the further increase of the thickness of the coal seam, the elastic core area in the coal pillar gradually decreases, resulting in the transition of the stress distribution state from bimodal to unimodal. In this process, the bearing capacity of the coal pillar is also weakened, and the stress value is gradually reduced. This trend reveals the important influence of coal seam thickness on the stress distribution and bearing capacity of coal pillars.  
The stress variation law of the entity coal under different coal seam thickness conditions is shown in Figure 15c. With the increase of the thickness of the coal seam, the peak stress of the entity coal side also shows a trend of increasing gradually, and the specific values are 25.9 Mpa, 29.9 Mpa, 32.2 Mpa, and 33.4 Mpa, respectively. Through in-depth analysis, we believe that an increase of coal seam thickness will induce a wider range of overlying strata movement and fracture in the stope, thus forming a larger range of stress arch. This change makes the stress on the coal pillar decrease, and the stress of the entity coal increases accordingly. Especially in the island working face of an extra-thick coal seam,  
Figure 14: (**a**) Stress distribution features of island working face under different working face; (**b**) the stress variation law and plastic zone evolution characteristics of coal pillar under different working faces; (**c**) fitting curve of peak stress of entity coal and working face length.  
due to the greater stress on the island working face, the stress concentration degree also increases, which greatly increases the possibility of rock burst. Therefore, in the design and mining process of an island working face of an extra thick coal seam, the influence of the coal seam thickness on the stress distribution of the working face must be fully considered, and effective measures must be taken to prevent rock burst and ensure the safety and stability of the mining operation.