# Study on the Stability and Control of Gob-Side Entry Retaining in Paste Backfill Working Face
## 5 Results of Numerical Simulation
### The Manifestation Law of Mining Stress in Working Face Under Different Backfill Ratios  
Under backfill ratios of 95%, 85%, 75%, and 65%, simulation of the working face advancing 150 m was conducted. Stress and displacement monitoring lines were arranged on the immediate roof 100 m behind the working face along the dip direction. Based on the monitoring results, the distribution curves of vertical stress and displacement on the immediate roof at different backfill ratios were plotted.  
From Figure 9, it can be seen that the vertical stress of the immediate roof above the GER roadway decreases sharply. At backfill ratios of 95%, 85%, 75%, and 65%, the minimum vertical stresses are 0.17, 0.75, 1.23, and 2.19 MPa, respectively. As the backfill ratio increases, the minimum vertical stress on the immediate roof above the roadway increases. The vertical stress on the immediate roof above the filled working face increases as the backfill ratio increases, and the stress distribution is generally smoother, with stress values stabilizing at approximately 8.80, 6.99, 4.03, and 2.96 MPa for backfill ratios of 95%, 85%, 75%, and 65%, respectively. Stress concentration occurs on the coal rib sides of roadway, with the peak vertical stress on the immediate roof above the coal rib sides at backfill ratios of 95%, 85%, 75%, and 65% being 18.4, 20.8, 23.4, and 26.7 MPa, respectively. The peak stress decreases as the backfill ratio increases. This indicates that as the backfill ratio increases, the backfill material can support the overlying rock layers more quickly and effectively, with the supporting effect on the roof becoming more pronounced. This enhances the ability of the backfill material to bear the load of the overlying rock layers, thus further reducing the mining-induced stress.  
Figure 9: Vertical stress curve of immediate roof with different backfill ratios.  
From Figure 10, it can be observed that the subsidence of the immediate roof decreases as the backfill ratio increases. At backfill ratios of 95%, 85%, 75%, and 65%, the maximum roof subsidence is 189, 438, 898, and 1360 mm, respectively. When the backfill ratio decreases from 95% to 85%, the reduction in maximum roof subsidence is relatively small. At this stage, the overlying rock layer only experiences bending subsidence and cracking. When the backfill ratio decreases from 85% to 65%, the supporting effect of the backfill material significantly decreases, and the space for the roof rotation increases, causing more intense mining-induced stress. The maximum roof subsidence increases from 438 mm to 1360 mm, and at this stage, the immediate roof and the main roof fracture, with a significant increase in roof subsidence and poor surrounding rock stability.  
In conclusion, as the backfill ratio increases, the fill material's efficiency in supporting the roof improves, reducing the space for roof rotation and subsidence. With an increased backfill ratio, the supporting capacity of the backfill material enhances, allowing it to bear the load of the overlying rock layers more effectively, thus restricting roof deformation. As the backfill rate increases, the height difference between the roof of the gob and the backfill material decreases, thereby limiting the space for roof subsidence. Consequently, the degree of mine pressure manifestation is reduced, and the peak stress within the coal rib decreases. The stress in the coal rib also recovers more quickly to its original rock stress.