## 4 Results and Discussion
### Influence of Different Parameters on the Support Structure  
(1) Shallow borehole diameter  
In this paper, the average value of normal stress of the surrounding rock near the anchors is taken as the effective binding force [44]. As can be seen from Figure 11, the effective binding force of the roadway side anchor and roof anchor is 6.12 MPa and 6.31 MPa, respectively, when pressure is without relief. With the increase in shallow borehole diameter, the effective binding force of the roadway side and roof anchor both continue to decrease, but the decrease in the roadway side anchor (6.01 MPa \(\rightarrow\) 4.53 MPa) is larger than that of the roof anchor (6.25 MPa \(\rightarrow\) 5.92 MPa), which shows that the deformation of the roadway surrounding rock is significantly enhanced under this condition. From this, it can be seen that the influence of boreholes on the roof anchors is weaker. As the diameter of the shallow borehole increases, the effective binding force of the anchor decreases, and de-anchoring is easy to occur when subjected to dynamic pressure. (2) Deep borehole diameter  
As can be seen from Figure 12, with the increase in deep borehole diameter, the effective binding force of roadway side and roof anchors is continuously reduced, but the reduction in roadway side anchors (6.10 MPa \(\rightarrow\) 5.88 MPa) is significantly larger than that of roof anchors (6.30 MPa \(\rightarrow\) 6.20 MPa). The effective binding force of anchors can  
Figure 11: The curve of the effective binding force of the anchor under different shallow diameters of the borehole. Figure 10: The curve of roadway surface deformation under different borehole spacing: (**i-v**) horizontal displacement. still be maintained above 5 MPa, and the location variable aperture is located outside the anchorage zone, so it has less influence on the support structure. 3 Variable aperture position  
As can be seen from Figure 13, with the increase in the distance between the variable aperture position and the roadway side, the effective binding force of the roadway side and the roof anchors both continue to increase, but the growth rate of the roadway side anchor (4.53 MPa \(\rightarrow\) 6.10 MPa) is significantly larger than that of the roof anchor (5.92 MPa \(\rightarrow\) 6.30 MPa). The closer the location of the variable aperture is to the roadway side, the smaller the effective binding force of anchors. When the location of variable aperture is inside the anchorage area, the effective binding force of the anchor decreases more, and when the location of variable aperture is outside the anchorage area, the effective binding force of the anchor is unaffected. Therefore, to ensure the strength of the support structure, the position of the variable aperture should be located outside the anchorage area. (4) Borehole spacing  
As can be seen from Figure 14, with the increase in borehole spacing, the effective binding force of roadway side and roof anchors is continuously reduced, but the growth of side anchors (6.11 MPa \(\rightarrow\) 4.96 MPa) is significantly larger than that of roof anchors (6.31 MPa \(\rightarrow\) 6.13 MPa), and the reduction is largest when the borehole spacing is 0.5 m.  
Figure 12: Curve of the effective binding force of anchor under different deep borehole diameters. Figure 13: Curve of the effective binding force of anchor under different variable aperture positions.