## 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  
To clarify the bearing characteristics of different coal pillar widths during double-roadway excavation using the FISH language roadway, the 21091, 21092, and 21102 roadways were excavated with each excavation step set at 5 m after calculating the equilibrium. Then, the next excavation cycle was carried out to determine the distribution of the coal pillar stress, the surrounding rock stress in the roadway, and the plastic zone during double-roadway excavation; the results are shown in Figure 7.  
Taking the center of the coal pillar as the origin, vertical stresses were measured at grid points located +20 m ahead and \(-\)20 m behind the coal pillar. The results indicate the following:  
1. When the coal pillar width was 5 m, the vertical stress within the coal pillar reached 6.08 MPa, slightly exceeding the initial stress of 5.5 MPa (1.11 times). At this point, the coal pillar reached its yield limit, with a predominance of grids in the plastic failure zone and fewer grids in the undamaged elastic region. 2. When the coal pillar width increased to 6 m, the vertical stress increased to 7.95 MPa, significantly higher than the initial stress (1.45 times). The bearing capacity of the coal pillar also increased to 1.45 MPa. 3. With a coal pillar width of 7 m, the peak stress increased to 9.21 MPa (1.67 times the initial stress). The number of grids in the elastic zone further increased, while the plastic zone remained intact, forming an elastic core area with a width of 1 m.
4. For a coal pillar height of 8 m, the peak stress exhibited a bimodal distribution, reaching 8.93 MPa (1.62 times the initial stress). The width of the elastic core area expanded to 2 m, with a significant increase in the number of grids in the elastic zone and a marked reduction in the number of grids in the plastic zone. 5. When the coal pillar widths were 9 m and 10 m, the peak stress remained bimodal, with values of 8.32 MPa (1.51 times the initial stress) and 8.01 MPa (1.46 times the initial stress). Compared to the 8 m coal pillar, the peak stress and stress concentration coefficient decreased substantially, while the width of the elastic core area increased  
Figure 7: Distribution of stress and plastic zone during the roadway excavation. to 3 m and 4 m. This led to a significant increase in the number of grids in the elastic zone, enhancing the bearing capacity and stability of the coal pillar. When the coal pillar width was relatively narrow (5-7 m), the corresponding bearing capacity increased gradually. During this phase, stress superposition within the coal pillar was more pronounced, resulting in a single-peak distribution of vertical stress. Consequently, the peak stress within the coal pillar increased progressively. Although the coal pillar exhibited some bearing capacity, the plastic zone either penetrated entirely or posed a risk of penetration. In such cases, external mining disturbances can easily cause the yielding and destruction of the coal pillar, leading to relatively low peak stress values. Conversely, when the coal pillar width was wider (8-10 m), stress superposition weakened, and the peak stress within the coal pillar exhibited a double-peak distribution. As a result, the peak stress showed a gradual decreasing trend. 2.2 Bearing Characteristics of Different Coal Pillar Widths During the Mining of the 2109 Working Face  
In order to study the bearing characteristics of different coal pillar widths during the first mining, the step distance of each mining was 10 m, and the cycle command was written in the FISH language for mining, and the parameters of the goat were the double-yield parameters shown in Table 4.  
To analyze the bearing characteristics of the coal pillar during the first mining of the 2109 working face, the simulation was terminated when the mining distance was equal to the width of the working face.