## 4 Study of the Bearing Characteristics of NCPDRE
### Analysis of Coal Pillar Stability Under the Influence of Full Dynamic Pressure  
According to the numerical simulation results of full dynamic pressure during roadway excavation, first mining, and secondary mining, the peak stress curve of the coal pillar under the influence of full dynamic pressure was drawn, which is shown in Figure 11.  
The peak stress of coal pillars across various mining stages was systematically analyzed through curve fitting. The fitting curves, as illustrated in the equation below, demonstrate that the GaussAmp function was employed for nonlinear fitting during roadway excavation and primary mining phases, while the exponential function was utilized for the secondary mining period. The correlation coefficients of 0.92, 0.94, and 0.99, respectively, indicate that the fitted curves accurately represent the data trends. As depicted in Figure 11, the analysis reveals that, during roadway excavation and first mining, the peak stress of coal pillars exhibited a gradual increase when the width was less than 8 m, followed by a gradual decrease when exceeding 8 m, establishing 8 m as the critical threshold for peak stress transition. During the second mining, the peak stress of 5-7 m coal pillars fell below the initial stress level, indicating the structural failure and loss of load-bearing capacity. Consequently, coal pillars of 8 m and above maintained residual bearing capacity, as substantiated by the experimental findings. Figure 11: The peak stress curve of the coal pillar under the influence of full dynamic pressure. The area and proportion of cross-sectional elastic zones in the roadway during the first and second mining were determined based on the cross-section of the coal pillar, and the area and proportion of elastic zones in the coal pillar under the influence of full dynamic pressure are shown in Figure 12.  
With the progressive increase in coal pillar width, a corresponding expansion in both the grid and the proportional extent of the elastic zone was observed across the roadway tunneling, first mining, and second mining stages. During the initial mining phase, the grid proportion of the elastic zone in the 7 m and 8 m coal pillars exhibited the most substantial reductions, decreasing by 13.39% and 14.07%. In comparison to the first mining stage, the secondary mining phase demonstrated a marked reduction in the elastic zone across all wider coal pillars. Notably, the elastic zone completely disappeared in the 5 m and 6 m coal pillars, while the area and proportion of the elastic zone in pillars of 7 m and above in width were significantly diminished. This phenomenon was substantiated by both the peak stress curve and the proportional analysis of the elastic zone:  
1. Following the primary mining operation, with the exception of the 5 m coal pillar, which exhibited a stress reduction of 2.39 MPa, all other width categories demonstrated stress increments of 0.55 MPa, 3.76 MPa, 3.09 MPa, 3.37 MPa, and 3.08 MPa. Notably, the stress increase in coal pillars of 7 m and above in width showed minimal variation. Concurrently, the elastic zone and its proportional extent across different width categories experienced measurable reductions. These observations indicate that while coal pillars of 6 m and above maintained load-bearing capacity under first mining stress conditions, the internal plastic zone underwent progressive development. This suggests a dual state of maintained structural integrity coupled with internal plastic deformation. 2. Subsequent to the second mining phase, comparative analysis revealed stress reductions of 2.31 MPa, 6.08 MPa, 9.12 MPa, 5.31 MPa, and 0.31 MPa in 5 m to 9 m coal pillars, respectively, in contrast to a 5.61 MPa increase in the 10 m pillar. The vertical  
Figure 12: The area of the elastic zone of the coal pillar under the influence of full dynamic pressure and its percentage.