## 4 Computational Results and Analysis
### Influence of the Strength of the Rock on the Mechanical Properties of Bolts Support  
Under different rock conditions, bolts exhibit different support schemes and anchoring effects. This is because the state of the rock affects the mechanical properties of the bolts. Considering this, the influence of the strength of the rock on the mechanical properties of bolt supports was studied. The rock mass is divided into soft, relatively hard, and hard rock masses, of which the computation schemes are shown as Schemes 1, 6, and 7 in Table 1. Therein, the computation of relatively hard rock mass has been performed in Section 4.1, and the computational results are displayed in Figure 5.  
Stress distributions on bolts in soft and hard rock masses are depicted in Figures 13a and 14a. Stress distributions on bolts in the relatively hard rock mass (Figure 5a) show that with the compression of rock mass, the stress on bolts in a rock mass with different strengths all increases at first, then decreases on the whole, and the peak stress always shifts to a greater depth. Whereas, the peak stress on bolts and maximum compressive displacement of rock mass differ greatly in rock masses of different strengths. In soft rock mass, the maximum compressive displacement reaches 7.5 mm while the peak stress intensity of bolts is only 59 MPa because soft rock mass is easily deformed. When gradually increasing the strength of rock mass, the maximum compressive displacements of relatively hard and hard rock masses are separately 5.1 mm and 4.4 mm, while the peak stress intensities of bolts gradually increase to 113 MPa and 136 MPa. This indicates that the strength of the rock only exerts a slight influence on the stress distribution law, while remarkable influences on the bolt stress and the maximum compressive displacement of the rock mass. Generally, at the failure of a rock mass without support, there are a large number of fractures in a soft rock mass while only a few in a harder rock mass. The fracture distribution at the failure of anchored rock mass is displayed in Figures 13b and 14b. According to Figure 5b, and by counting the number of fractures, fractures are distributed in a similar way in anchorage bodies with three strengths; that is, fractures are mainly distributed in the rock mass. Therefore, the failure mode is manifested as damage to the rock mass. In the meantime, the total number of fractures gradually reduces with the improvement in the strength of the rock, while the number of fractures in the grouts gradually increases. This indicates that the higher the strength of the rock of anchored rock mass, the easier the development of fractures in the grouts. Therefore, it becomes necessary to improve the strength of grouts when anchoring surrounding high-strength rocks to avoid failure of the anchored rock mass due to failure of the grout. Figure 13: Stress distribution and fracture distribution on bolts in soft rock mass. (**a**) Stress distribution of bolts; (**b**) Fracture distribution at failure. Changes in the anchorage forces of bolts in rock mass with different strengths with the compressive displacement of rock mass are illustrated in Figure 15. As the rock mass is compressed, the anchorage force of bolts in all rock mass gradually grows, and that of bolts in hard rock mass grows fastest. With the improvement in the strength of the rock, the maximum anchorage forces of bolts are 90 kN, 156 kN, and 188 kN, showing a large increase in amplitudes, which implies that the strength of the rock greatly affects the anchorage force of bolts. Figure 16 shows the values of evaluation indices for the support capacity of bolts in a rock mass with different strengths. It can be seen that as the strength of the rock increases, displacement of the bolt head and the number of fractures in anchored rock mass both gradually decrease, while the peak stress on the bolts gradually increases.