## 5 Results and Discussion  
### Results  
#### 5.1.1 Vertical Displacement of KS in Overlying Strata  
1. The collapse and displacement of 7 KS in the overlying strata of the strip goaf 1513 lateral to the BHR 1513 are shown in Figure 7 (data from monitoring line A), and the following can be learned: 1. Before mining the working face 1511, the vertical displacement in monitoring line A of all 7 KS gradually increases to different extents from left to right (extend from the solid coal sidewall of BHR 1513 towards the strip goaf 1513). Among them, the monitoring line vertical displacement of KS1 increases from 279 mm to 374.5 mm, an increase rate of 34.2%. The monitoring line vertical displacement of KS2, KS3, KS4, KS5, KS6, and KS7 sees an increase of 15.9%, 6.8%, 4.8%, 2.7%, 1.0%, and 0.3%, respectively. This increase in vertical displacement is defined as the KS rotation degree of the later Strip goaf 1513 of the BHR 1513; 2. When the mining of the working face 1511 is gradually progressed towards the right to 30 m, the vertical displacement in the monitoring line of all 7 KS gradually increases. Among them, the rotation degree of KS1 increases from 34.2% to 35.1%; the rotation degree of KS2 increases from 15.9% to 16.9%; the rotation degree of KS3 increases from 6.8% to 7.9%; the rotation degree of KS4 increases from 4.8% to 5.9%; the rotation degree of KS5 increases from 15.9% to 16.9%; the rotation degree of KS6 increases from 1.0% to 2.7%; and the rotation  
Figure 6: Arrangement of monitoring points: (**a**) arrangement of measuring lines A for vertical displacement of KS; (**b**) arrangement of measuring lines B for vertical displacement of KS; (**c**) arrangement of monitoring points for surface displacement of BHR 1513 and vertical stress and vertical displacement above coal pillar A; and (**d**) arrangement of monitoring points for vertical stress and vertical displacement above coal pillar B.  
degree of KS7 increases from 0.3% to 2.4%. It can be concluded that when working face 1511 mines to 30 m, all the 7 KS subside and rotate at the same time with a small rotating increase rate, showing the trend of overall subsidence;
3. When the mining of the working face 1511 is gradually progressed towards the right to 60-90 m, the vertical displacement in the monitoring line of all 7 KS increase more obviously. As shown in Figure 7, when the working face 1511 mines to 60 m, the rotation degree of the 7 KS begins to accelerate increasingly, in other words, 60 m is the inflection point of rotation degree of KS.  
Figure 7: Cont.  
2. The collapse of coal pillar B and main roof above lateral goal 1511 (data from Monitoring line B) are shown in Figure 8, and the following can be learned: 1. Before the mining of working face 1511, coal pillar B and goat 1511 do not exist at this time, and the vertical displacement of rock strata in the measuring line segment KS1 shows a trend of increasing from left to right (inline to strip goat 1513); 2. When the working face 1511 is gradually mined towards the right to 30-60 m, the vertical displacement of rock strata in KS1 continues to increase, and the curve is relatively flat, showing a trend of overall subsidence; 3. When the working face 1511 is gradually mined towards the right to 90 m, the vertical displacement of rock strata in the measuring line segment KS1 further increases, showing a trend of increasing from left to right (rotate towards the direction of goat 1511).