## 2 Project Background and Calculation Method
### Calculation Method
#### 2.2.2 Determination of Rock Reduction Parameters  
1. Hoek-Brown criterion parameterization (1) GSI value determination The Hoek-Brown criterion parameters were determined on the basis of the distribution profiles of rock layers and the surrounding rock grades in the new tunnels, the overtopping geological forecast, and the observation information of the palm face, combined with the GSI index map proposed by [PERSON] et al. (2018). 1. Rock layer and surrounding rock grading section The new Wanshoushan Tunnel is a double-line highway tunnel, the left line intersects with Hurong Railway Tunnel at K3+674.943 (Figure 2 L0) and the right line intersects with Hurong Railway Tunnel at YK3+694.291 (Figure 3 R0). The 60 m before and after the intersection point of the new highway tunnel is the excavation-sensitive area ([PERSON] et al., 2018). Preliminarily, the excavation sensitive area is determined as Class IV surrounding rock. Typical cross-sections of 60 m and 85 m before and after the tunnel intersection are extracted for analysis; the left line includes L1 section K3+590, L2 section K3+615, L3 section K3+735, and L4 section K3+760; and the right line includes R1 section YK3+609, R2 section YK3+634, R3 section YK3+754, and R4 section YK3+779. \begin{table}
\begin{tabular}{l l} \hline \hline
**Description of Rock Excavation Methods and Effects** & \(D\)**Value** \\ \hline Very little disturbance, good blasting or tunnel boring machine excavation & 0 \\ Small disturbances, poor rock mass with mechanical or manual excavation & 0 \\ Large disturbances, stress concentrations causing the tunnel bottom to bulge & 0.5 \\ High disturbance, poor blasting results & 0.8 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Table of rock disturbance coefficients in tunneling. Figure 3: Grading section of rock layers and surrounding rocks in the right lane of the new tunnel. Figure 2: Grading section of rock strata and surrounding rocks in the left lane of the new tunnel. The surrounding rocks of the L1 and L2 sections are mainly medium-weathered grayish-white malmstone, with a good integrity and interlayer combination, undeveloped joints and fissures, and a dry palm surface. A small amount of mudstone locally exists in L1, with medium-thickness bedding, while thick bedding is dominant in L2. The surrounding rock of the L3 section is mainly mudstone, which is a soft rock. The rock body is relatively broken, mainly in thin layers; the combination between rock layers is general; joints and fissures are developed; strong weathering is dominant; and the palm surface is dry. The surrounding rocks in section L4 are mainly mudstone and there are obvious malmstone and mudstone interlayers within 2 m above the upper step, of which mudstone is a soft rock and malmstone is a hard rock. The rock body is more complete, the combination between the rock layers is general, the joints and fissures are developed, medium weathering is dominant, and the palm surface is drier. The radar reflection signals of the L1 and L2 sections are strong and the frequency change of electromagnetic wave signals is general and continuous in the same direction; L1 is dominated by medium-low frequency signals and L2 is dominated by medium-high frequency signals. Combined with the condition of the palm surface of the section, it is concluded that the 0-25 m section in front of the L1 and L2 section is mainly malmstone, which belongs to the harder rock; the joints and fissures are not developed; and the integrity of the rock body is better and the surrounding rock is denoted as level IV. The L3 section radar reflection signal is strong; the electromagnetic wave signal frequency change is general, mainly in the middle and high frequency signals; the isotropic axis is intermittent and local continuous, with no obvious shock wave signal.