## 3 Deformation Characteristics and Forced Mechanism of Roadway W 23021
### Numerical Simulation
#### 3.2.4 Stress Distribution Simulation Results  
The reused roadway suffered two mining operations, so the analysis should be in a dynamic view [41]. According to the field monitoring and mine pressure theory, roadway W 23021 was reserved on the side of goat and suffered the lateral abutment pressure during the first mining (coalface W 2301). During the second mining, roadway W 23021 became deformed ahead of coalface W 2302 and was abandoned up to behind it, so the roadway W 23021 suffered the leading abutment pressure. The 3D contours of the vertical stress of the coal seam are shown in Figure 9, and the vertical stress contours of monitoring section during the two mining operations are shown in Figures 10 and 11. Figure 8: Deformation curves of numerical simulation and field monitoring. (**a**) During the first mining (coalface W2301); (**b**) During the second mining (coalface W2302). Figure 9a indicates that the vertical stress of the coal seam was concentrated on the side of the coalface, forming the lateral abutment pressure during the first mining operation(coalface W 2301). The range of the lateral abutment pressure covered the reused roadway W 23021 and W 23025. The pillar between the two roadways has yielded plastic deformation and the stress was reduced. The stress in the area outside the roadways was increased obviously. Figure 9b shows that the vertical stress of the coal seam was increased in front of coalface W 2302 during the second mining, which is called the leading abutment pressure. The stress state in the area outside the roadway W 23021 was influenced obviously by this leading abutment pressure. Figure 10: Vertical stress contours of monitoring section during the first mining. (**a**) 50 m ahead of coalface W 2301; (**b**) 0.5 m behind coalface W 2301; (**c**) 50 m behind coalface W 2301; (**d**) 100 m behind coalface W 2301; (**e**) 150 m behind coalface W 2301; (**f**) 200 m behind coalface W 2301. Figure 9: 3D contours of vertical stress in coal seam. (**a**) First mining (coalface W 2301 advanced 350 m); (**b**) Second mining (coalface W 2302 advanced 100 m). The phenomena of stress concentration on two sides of roadways can be seen from Figure 10, and the vertical stress is increased with the advancing of the coalface, which reflects the influence of lateral abutment pressure of coalface W 2301. When the monitoring section is 50 m ahead of coalface W 2301, the maximum value of concentrated stress on the right side of roadway W 23025 is about 18 MPa (Figure 10a). With the advancement of the coalface, the concentrated stress is increased to about 22 MPa and its range is also rapidly enlarged until the monitoring section is 150 m behind of coalface W 2301, which corresponds to the violent deformation stage (Figure 10e). Then, the concentrated stress and its range are increased slowly. After the monitoring section was placed 200 m behind coalface W 2301, the concentrated stress and its range became stable and no longer changed obviously, which corresponds to the plateaued deformation stage. Hence, a permanent deformation is achieved at this moment. Figure 11 shows that the concentrated stress and its range are increased further because of the second mining of coalface W 2302. It was noticed that the concentrated stress and its range are gradually increased with the advancing of coalface W 2302. When the monitoring section is 100 m ahead of coalface, the maximum value of concentrated stress on the left side of roadway W 23021 is 18 MPa. Then it increased rapidly to 28 MPa with the coalface advancing. The concentrated stress on the right side of roadway W 23021 is almost identical. Hence, the roadway deformation became more serious in front of coalface W 2302. The numerical simulation revealed that the reused roadway was significantly affected by the lateral abutment pressure during the first mining, and it was significantly affected by the leading abutment pressure during the second mining.