## 4 Roof Control Effect during Retention Stage
### Roof Control Effect during Primary Mining Retention Stage  
During the mining period of the 7135 working face, the measured resistance of the stacking supports and the roadway roof formation effect during retention reflect the control effectiveness.  
1. Stress analysis of reinforcing anchor cables  
During the movement of the gob-side roadway roof, the stress of the reinforcing anchor cables can reflect the roof collapse process and state. As shown in Figure 14, the resistance-increasing section of the reinforcing anchor cables occurs from 40 m ahead of the working face to 60 m behind the working face. Affected by the pre-splitting blasting and advanced mining, the resistance-increasing rate of the anchor cables ahead of the working face is significantly higher than that of the anchor cables behind the working face. The tension of the anchor cables increases from 230 kN to 304 kN. During this stage, the roadway roof undergoes pre-splitting blasting, fracture movement, and subsequent consolidation.  
Figure 14: Stress curve of anchor cable.  
Figure 13: Roof support parameters during primary mining retention Stage: (**a**) Cross-section diagram of roof support behind working face. (**b**) Plan of roof support behind working face.  
Behind the working face, due to the roadway roof experiencing pressure relief, fracture, subsidence, and gradual compaction, the tension of the anchor cables first decreases and then increases until it stabilizes. After 90 m behind the working face, the tension of the anchor cables stabilizes at 316 kN, indicating that the roof on the gob side has fully collapsed and compacted along the pre-splitting surface. Due to the sinking and then stabilizing trend of the roof during the cutting to retaining period, the tension value of the anchor cables after the retaining period is significantly higher than that of the anchor cables at the stable stage ahead of the working face.  
Analysis of stack-type support resistance During the mining period of the working face, the ZQ4000/20.6/45-type advanced support hydraulic support for the roadway, namely the stacking support, was used to temporarily reinforce and support the roof of the retained roadway. The rated working resistance of the stacking support was 41.6 MPa. The measured variation in the working resistance of the stacking support is shown in Figure 15. During the mining period, the measured resistance of the stacking supports changes, as shown in Figure 15.  
The resistance of the stacking supports increases from 35 m ahead of the working face to 70 m behind the working face. Between 25 m ahead of the working face and 15 m behind the working face, the supports are affected by the periodic pressure from the working face, and the resistance changes significantly. The 15 m to 30 m range behind the working face is the stage of increased resistance for the stack-type supports. As the retention distance increases, the support resistance fluctuates, generally stabilizing, with a maximum working resistance of 40 MPa, which falls within the reasonable range of resistance changes for the supports.  
Observing the roadway roof control effect, as shown in Figure 16, the roof formation is complete during the retaining period, without large deformations or structural instability. The roadway formation effect is good, meeting the requirements of ventilation, pedestrian traffic, and safe mining.  
Figure 15: Variation curve of working resistance of stack-type support.