## 4 Study of the Bearing Characteristics of NCPDRE
### Numerical Simulation Modelling
#### 4.2.1 Bearing Characteristics of Different Coal Pillar Widths During Double-Roadway Excavation
The measurement line arrangement, as depicted in Figure 8a, was established with the coal pillar's center as the origin. This setup facilitated the acquisition of vertical stresses within the coal pillar grid spanning from \(-\)5 m to +25 m. The findings are as follows:  
1. For a 5 m coal pillar, the vertical stress measured 3.69 MPa, which was below the initial stress (0.67 times). This indicates the occurrence of yield failure in the coal pillar, predominantly characterized by a plastic failure network structure, with minimal presence in the elastic zone. 2. In the 6 m coal pillar, the peak stress reached 8.5 MPa, exceeding the initial stress (1.55 times). This suggests that the coal pillar retained some bearing capacity, with a minor elastic component present and incomplete plastic failure development. 3. When the coal pillar measured 7 m, the peak stress increased to 12.97 MPa (2.36 times the initial stress). While the bearing capacity became more pronounced, the coal pillar remained unstable due to extensive plastic failure grids and plastic infiltration. 4. For the 8 m coal pillar, the stress curve exhibited an approximate double-peak pattern, with a peak stress of 12.02 MPa (2.19 times the initial stress). The elastic core width measured merely 1 m, showing increased width and grid count in the elastic zone compared to the 7 m pillar, alongside a significant reduction in plastic zone grids. 5. In the 9 m and 10 m coal pillars, the peak stress demonstrated a distinct bimodal pattern, measuring 11.69 MPa (2.13 times the initial stress) and 11.09 MPa (2.02 times the initial stress), which were reduced compared with the 8 m coal pillar. By contrast, the width of the elastic core area and the number of grids in the elastic zone significantly increased, and the bearing capacity and stability were improved. Figure 8: Distribution of stress and plastic zone during the 2109 working face mining. During the first mining, the change in the stress peak value was relatively small, and the stress value did not significantly change. The peak value of the stress in the coal pillar was the same as that in the mining period, which increased rapidly to the maximum with the increase in the width of the coal pillar, and then gradually decreased. At this time, the bearing capacity and failure of the coal pillar were the same in the first mining period. 2.3. Bearing Characteristics of Different Coal Pillar Widths During the Mining of the 2110 Working Face  
To study the bearing characteristics of different coal pillar widths during the mining of the 2110 working face, for which the same mining scheme was used as the first mining, the bearing characteristics of different coal pillar widths were analyzed during the secondary mining. Both sides of the coal pillar after the second mining were goaf areas, and the measurement line of the coal pillar was arranged. The results are shown in Figures 9 and 10.  
its peak value demonstrated corresponding growth. The maximum vertical stress for 5 m to 7 m coal pillars remained significantly below the initial stress. In contrast, the 8 m coal pillar showed a maximum vertical stress slightly exceeding the initial stress, while the 9 m and 10 m coal pillars exhibited maximum vertical stresses that were 2.07 and 3.04 times the initial stress. 2. The analysis of the plastic zone contour diagram reveals that the lattice structures of both 5 m and 6 m coal pillars underwent plastic failure. When the coal pillar width exceeded 7 m, the majority of the lattice structures experienced plastic failure, with only a limited number of elastic lattices remaining. The plastic zones beneath each coal pillar width were fully penetrated, leaving no elastic core area. However, as the coal pillar width increased, there was a gradual augmentation in the number of lattice structures within the elastic zone.