## 3 Quality Grade Survey of Surrounding Rock Mass
### Selection of Support Patterns Based on Rock Quality Grading  
Dangerous rocks are present on the roadway surface due to the compromised structural integrity of the deep roadway, as indicated by the deformation characteristics and survey findings. Shotcrete is employed to reinforce the surrounding surface rocks, preventing weathering and falling, and providing essential support for the roadway. While shotcrete effectively stabilizes the surface rock mass, it is insufficient for deeply fractured  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Rating** & **\textless{}20** & **21–40** & **41–60** & **61–80** & **81–100** \\ \hline Quality grading & V & IV & III & II & I \\ Quality & Worse rock & Poor rock & Ordinary & Good rock & Better rock \\ description & mass & mass & rock mass & mass & mass \\ \hline \hline \end{tabular}
\end{table}
Table 4: Rock mass grading and evaluation by RMR.  
Figure 4: On-site drilling and coring: (**a**) No.6 transportation roadway; (**b**) No.7 transportation roadway.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**No.** & \
\begin{tabular}{c} **Uniaxial** \\ **Compressive** \\ **Strength \(\sigma_{1}\) (MPa)** \\ \end{tabular} & \(R_{1}\) & **RQD** & \(R_{2}\) &
\begin{tabular}{c} **Joint Spacing** \\ **(m)** \\ \end{tabular} & \(R_{3}\) \\ \hline
1 & 26.77 & 4 & 16.31 & 2.68 & 0.12 & 9.15 \\
2 & 15.88 & 2 & 14.42 & 2.48 & 0.09 & 8.13 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Relevant parameters and scoring values.  
surrounding rocks. To adequately address the varying support requirements, it is crucial to implement support systems that strengthen both shallow and deep rock masses. The support for shallow rock typically involves surface treatments, such as shotcrete and mesh, which focus on preventing immediate rock fall. In contrast, deep rock stabilization requires more robust solutions, such as anchor bolts used in anchor net supports that extend deeply into the surrounding rock. This approach directly enhances the stress distribution within the surrounding rocks, particularly for those with complex structural surfaces. By recognizing and addressing the differences in support needs between shallow and deep rock masses, we can ensure a safer and more stable underground environment.  
Under the reinforcement of the anchor bolts, the deep surrounding rock within the reinforcement range forms a structure similar to a load-bearing arch. At the same time, the surface metal mesh encapsulates the roadway surface, providing surface support and playing a crucial role in supporting the surrounding rock in the tensile stress zones between the anchor bolts. The overall support effect is further enhanced by reinforcing the system with double ribs and pallets. [PERSON] proposed a series of support rules based on the classification of geological mechanics, tailored for the selection of support systems in roadways (Table 5). Locally broken mines and rock mass for the level-IV surrounding rocks require support through anchor nets or anchor net spray. Rock supports for No.6 and No.7 transportation roadways in the middle section of the Baoxin-120 district at Shilu Iron Deposit adopt anchor net spray according to the support guidelines and on-site situation. [PERSON] et al. (2016) evaluated rocks in the Pelosika Dam tunnel project using the RMR method, categorizing them as inferior. The appropriate excavation sequence involves the heading excavation step method and the multiple-incremental hole drilling method. The vaults and walls are supported by anchor bolts installed in the system, made of medium and light steel ribs, reinforced by steel mesh and shotcrete.