## 2 Project Background and Calculation Method
### Calculation Method
#### 2.2.2 Determination of Rock Reduction Parameters
Combined with the situation of the palm surface in the L3 section, it is concluded that mudstone dominates in the range of 0-25 m, at the front of the L3 section--mudstone is a soft rock, with developed joints and fissures--while the integrity of the surrounding rock is more typical and there are weak and soft surrounding rock segments in the local area; as such, it is a class IV deviation surrounding rock. The radar reflection signal of the L4 section is strong and the frequency change of the electromagnetic wave signal is typically dominated by a homogeneous medium-low frequency signal, with continuous isotropic axis and no obvious shock wave signal. Combined with the situation of the palm face of the L4 section, it is concluded that mudstone is dominant in the range of 0-25 m, at the front of the L4 section. Furthermore, there may be malmstone and mudstone interbedding in the local area, of which mudstone is a soft rock and malmstone is a harder rock, with developed joints and fissures, while the integrity of the surrounding rock is more typical; as such, it is a class IV surrounding rock. Observation and radar data analysis of the right line palm surface  
Observed photographs and radar data of the palm face of the four sections of the left line, exemplified by the R\({}_{1}\) photographs, are shown in Figures 7 and 8. Figure 7: R\({}_{1}\) photographs of sectioned palm faces. The surrounding rocks in section R1 are mainly gray-white malmstone; the rock body is complete, mainly with medium-thick lamination; the combination between the rock layers is good; the joints and fissures are not developed; mainly medium weathering is present; and the palm face is dry. The surrounding rocks in section R2 are mainly malmstone, mixed with mudstone--malmstone and mudstone are both soft rocks--and there is an obvious interlayer in the middle of the palm face. The surrounding rocks are mainly medium-thick bedded, the integrity of the rock body is typical, the combination between the rock layers is typical, the joints and fissures are developed, strong weathering is dominant, and the palm surface is dry. The surrounding rocks in section R3 are mainly mudstone and malmstone; mudstone is a soft rock and malmstone is a hard rock. The rock body is more broken, mainly in thin layers, and the combination between the rock layers is poor. The R4 section is mainly surrounded by mudstone, which is a soft rock; is surrounded by thin layers; the integrity of the rock body is typical; and the combination between rock layers is generally better. The R3 and R4 sections have developed joints and fissures, which are mainly strongly weathered, and the palm surface is dry. The radar reflection signal is stronger in section R1 and weaker in section R2. The R1 and R2 sections' electromagnetic wave signal frequency change is typical, mainly in the low-frequency signal region, and the isotropic axis is intermittent. Combined with the condition of the palm surface, it is concluded that the 0-25 m section surrounding sections R1 and R2 is dominated by malmstone, which belongs to the harder rock, but mixed with mudstone, which belongs to the softer rock. The joints and fissures are developed, and the rock body integrity is typical, resulting in it being a class IV surrounding rock. The R3 section's radar reflection signal is strong and its electromagnetic wave signal frequency change is typical, mainly in the middle- and high-frequency signal regions, and the same direction axis is locally continuous, locally intermittent, and its amplitude is typical. Combined with the condition of the R3 section's palm face, it is concluded that the 0-25 m range is dominated by mudstone and malmstone, with mudstone belonging to the softer rock and malmstone belonging to the harder rock. The joints and fissures are developed in the range of 0-10 m in front of the palm face, and the integrity of the peripheral rock is typical; as such, it is a peripheral rock of level IV deviation.