## 3 Case Study
### Input and Output Variable Selection  
The original field data were collected from the left line (130-300 rings). During the tunneling, the shield machine was oriented by the navigation system. The measurement accuracy was high, and the front horizontal deviation (FHD), front vertical deviation (FVD), back horizontal deviation (BHD), back vertical deviation (BVD), rolling angle (RA), pitch angle (PA), and other parameters were measured (Figure 5). Here, four attitude parameters (FHD, FVD, BHD, and BVD) of the shield machine measured by the system were used to quantify the driving attitude trajectory. Figure 6 shows the path projection view and attitude position parameters of the shield machine. When the shield head or tail was on the right side of the designed tunnel axis (DTA) along the driving direction, the horizontal deviation was positive. When the shield head or tail was higher than the DTA, the vertical deviation was positive. The four attitude parameters were continuously monitored to provide a reference for the adjustment of the attitude trajectory. Thus, they were selected as the output parameters of the predictive model. Figure 5: Shield machine and attitude angle. The input parameters of the model comprised shield tunneling, geometric, and geological parameters. Operational parameters were obtained from the shield-machine equipment, such as the propulsion and guide systems. These parameters included the CS, CT, pressure in each pushing interval, TH of the propulsion cylinder, upper and lower stroke difference (SD), penetration (P), cutting face pressure (FP), deflection moment in the y-direction (MY), cut water pressure, and No.01-No.56 propulsion cylinder pressure (S01-S56). The geometric parameters included the pitch angle (PA), rolling angle (RA), hinged horizontal deviation (HHD), hinged vertical deviation (HVD), and cover depth (CD). Other geometric parameters, such as the tunnel diameter, shape, and slope, were unchanged. Geological parameters were obtained from the geological exploration data of the project, including soil weight (SW), cohesion (C), internal friction angle (IFA), and compression modulus (CM). Summarily, 170 sets of data from 130 to 300 rings of the Zhuhai Xingye Express Tunnel project were used as the database. Considering the influence of the shield tunneling, geological, and geometric parameters, 82 input parameters were selected. Four groups (FHD, FVD, BHD, and BVD) of characteristic shield-attitude trajectory parameters were predicted (Table 4). \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Number** & **Parameters** & **Min** & **Max** & **Mean** & **Unit** \\ \hline
1 & Cutter speed (CS) & 0.78 & 1.06 & 0.99 & rpm \\
2 & Cutter torque (CT) & 1077 & 6296 & 2912 & kN-m \\
3 & Upper pressure (UP) & 3.5 & 17.2 & 7.5 & MPa \\
4 & Left upper pressure (LUP) & 2.8 & 15.7 & 9.1 & MPa \\
5 & Left lower pressure (LLP) & 0.1 & 28.9 & 12.2 & MPa \\
6 & Lower pressure (LP) & 8.6 & 25.3 & 14.8 & MPa \\
7 & Right upper pressure (RUP) & 0.2 & 14.5 & 8.2 & MPa \\
8 & Right lower pressure (RLP) & 0.1 & 23.0 & 11.7 & MPa \\
9 & Thrust (TH) & 63,144 & 113,463 & 84,850 & kN \\
10 & Upper and lower stroke difference (SD) & \(-\)41 & 203 & 90 & mm \\
11 & Penetration (P) & 2.0 & 32.0 & 9.4 & mm/r \\
12 & Cutting face pressure (FP) & 0.23 & 0.26 & 0.24 & MPa \\
13 & Deflection moment in the y-direction (MY) & \(-\)22,047 & 3418 & \(-\)5330 & kN-m \\
14 & Right cut water pressure (PT2) & 2.325 & 2.668 & 2.462 & bar \\
15 & Left cut water pressure (PT3) & 2.318 & 2.655 & 2.456 & bar \\
16 & Right upper cut water pressure (PT0) & 1.578 & 1.903 & 1.703 & bar \\
17 & Left upper cut water pressure (PT1) & 1.575 & 1.898 & 1.700 & bar \\
18 & No.01–No.56 propulsion cylinder pressure (SP1–SP56) & 0.0 & 28.9 & 10.6 & MPa \\
19 & Pitch angle (PA) & \(-\)0.55 & 0.41 & 0.16 & degree \\
20 & Rolling angle (RA) & \(-\)0.40 & 0.17 & 0.30 & degree \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Statistics for input and output parameters.