## 6 Conclusions  
1. A comprehensive mechanical model of the immediate roof following upper section working face mining was developed, incorporating the derived relationship between the coal pillar bearing load and the immediate roof length. The bearing stress characteristics of coal pillars in Qingwa Coal Mine were categorized into three distinct phases: the steep decline stage (0-4 m), transition stage (4-7 m), and stabilization stage (>7 m). Coal pillars within the stabilization phase's width range demonstrated measurable strength surplus capacity, indicating enhanced structural integrity.
2. Through numerical simulation analysis, the bearing characteristics of 5 m-10 m coal pillars were systematically examined across roadway excavation, first mining, and second mining. The investigation revealed that, for 5 m-7 m pillars, significant internal stress superposition occurred, manifesting as a single-hump distribution pattern with progressively increasing peak stress. Conversely, 8 m-10 m pillars exhibited reduced internal stress superposition, characterized by a double-hump distribution pattern with gradually decreasing peak stress. During the first mining operation, the vertical stress distribution within the pillars transitioned from single-hump to double-hump configurations as the width increased. Second mining analysis demonstrated complete plastic failure in the 5 m and 6 m coal pillar meshes, while the 7 m and wider pillars showed extensive plastic damage with fully penetrated plastic zones across all width categories.
3. Under the influence of full dynamic pressure, the 5-7 m coal pillars yielded and were destroyed, whereas the 8 m and above coal pillars had certain residual bearing capacity, compared with the first mining. After the second mining, the elastic zone grid of each width of the coal pillar was sharply reduced. The 5 m and 6 m coal pillars were no longer in the elastic grid, whereas the elastic zone grid area and proportion of the 7 m and above coal pillars were very low. In order to avoid plastic zone penetration after the first mining, it was determined that the optimal width of NCPDRE was 8 m.
4. The observation and analysis of the displacement of the roadway surface under the influence of full dynamic pressure showed that the first mining had a greater influence on the displacement of the roof and floor of the roadway, followed by the solid coal side, whereas the displacement of the coal pillar side was smaller; the second mining had a greater influence on the floor, followed by the coal pillar side and the solid coal side, whereas the displacement of the roof had a smaller influence.  
Figure 14: Maximum surface displacement and its amplitude in lanes 21092 and 21102: (**a**) maximum surface displacement and its increase in the 21092 roadway; (**b**) maximum surface displacement and its increase in the 21102 roadway.  
**Author Contributions:** Conceptualization, W.G.; methodology, W.G.; software, D.X., J.P., and H.Z.; validation, H.Z. and D.X.; formal analysis, S.W. and H.Z.; investigation, H.T. and D.X.; resources, W.G.; data curation, H.Z.; writing--original draft preparation, H.T. and Z.H.; writing--review and editing, H.Z. and W.G.; visualization, D.X.; supervision, W.G.; project administration, D.X.; funding acquisition, W.G. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research was funded by the National Natural Science Foundation of China, grant number 52274103.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** The raw data supporting the conclusions of this article will be made available by the authors upon request.  
**Conflicts of Interest:** The authors declare no conflicts of interest.