## 3 Project Overview and Data Preprocessing
### Data Acquisition and Processing  
This study collected 400 sets of TBM tunneling performance data under different surrounding rock grades by combining the on-site excavation data from the KS Tunnel project. These datasets cover four surrounding rock types: II, IIIa, IIIb, and IV. The TBM tunneling parameters primarily include machine parameters, excavation performance parameters, and excavation index parameters. These parameters consist of the thrust (F), rotation speed (N), torque (T), net penetration rate (PR), penetration depth (p), field penetration index (FPI), torque penetration index (TPI), and specific excavation energy (SE). The distribution of each indicator in the engineering cases above is statistically presented in Figure 2. And the statistical characteristics are described in Table 2. The dataset validates the generalization ability of the model established in this study. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Component Location** & **Component Names** & **Component Parameters** \\ \hline \multirow{3}{*}{Hard rock tunnel} & Machine type & Open-type \\  & Overall machine length (m) & 200 \\  & Tunneling progress (mm) & 1800 \\  & Installed net horsepower power (kW) & 4400 \\ \hline \multirow{3}{*}{Cutter tools} & Rated total thrust power (kN) & 14,373 \\  & Maximum total thrust power (kN) & 22,934 \\ \cline{1-1}  & Excavation diameter (mm) & 7030 \\ \cline{1-1}  & Cutterhead tool rated load (kN) & 315 \\ \hline \multirow{3}{*}{Cutterhead drive} & Drive type & Variable frequency motor drive \\ \cline{1-1}  & Total power (kN) & 350 \(\times\) 8 = 2800 \\ \cline{1-1}  & Cutterhead rotation speed (rpm) & 0–10.9 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Main parameters of TBM 7(TBM 8). \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Description Indicators** & **PR** & **p** & **F** & **N** & **T** & **FPI** & **SE** & **TPI** \\ \hline Max & 74.00 & 12.00 & 16,618.66 & 7.47 & 2762.63 & 766.04 & 1613.24 & 890.00 \\ Min & 0.12 & 0.01 & 11.63 & 0.10 & 27.67 & 11.21 & 6.00 & 45.03 \\ Mean & 41.56 & 6.50 & 10,923.45 & 6.38 & 1518.23 & 48.96 & 58.07 & 297.64 \\(1) Thrust (F): The distinction between the different surrounding rock grades is outstanding, making it suitable for the classification of surrounding rock grades. (2) Torque (T) demonstrates good discriminative ability among the IIIa, IIIb, and IV surrounding rock types, but there is an overlap between II and IIIa. Overall, the average torque can be used to distinguish between the different classes of surrounding rock. (3) Rotation speed (N) shows a high degree of overlap in the distribution among the various classes of IIIa, IIIb, and IV surrounding rock, making it difficult to distinguish between different rock grades effectively. Under II and IIIa surrounding rock conditions, the rotation speed values are relatively concentrated, while in the IIIb and IV conditions, the box in the boxplot is noticeably longer, suggesting a more dispersed range of cutter  
Figure 2: Distribution of TBM tunneling parameters under different surrounding rock grades: (**a**) the thrust (**F**); (**b**) penetration rate (PR); (**c**) rotation speed (N); (**d**) the torque (T); (**e**) field penetration index (FPI); (**f**) penetration depth (p); (**g**) specific excavation energy (SE); and (**h**) torque penetration index (TPI). head rotation speeds. This dispersion might be due to unstable geological conditions, resulting in the cutter head rotation speed being significantly influenced by the geological environment. Overall, the average rotation speed can effectively reflect the different classes of surrounding rock encountered during the TBM excavation process. (4) The penetration rate (PR) can effectively differentiate the latter three classes of surrounding rock, with an overlap occurring only between the II and IIIb surrounding rock types. The PR in the IV surrounding rock type is the lowest, with a noticeably elongated box in the boxplot, indicating a more dispersed average net penetration rate.