## 3 Discussion of Analysis Results  
This section discusses the applicability of the proposed model and the numerical analysis results for the measured torque and thrust force, the monitored chamber pressure, the discharged volume and discharge rate of particles, and the surface settlement.  
\begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**Case Number**} & **Rotational Speed of Cutter** & **Rotational Speed of Screw** \\  & **Head, \(\omega_{cutter}\) [rpm]** & **Penetration Rate, \(PR\) [mm/s]** & **Conveyor, \(\omega_{screw}\) [rpm]** \\ \hline
1 & & 5 \\
2 & & 0.5 & 10 \\
3 & 2 & 1 & 5 \\
4 & & 10 \\
5 & & Automatically controlled \\  & & (initial \(PR\) = 0.5 mm/s and \(\omega_{screw}\) = 10 rpm) \\ \hline \hline \end{tabular}
\end{table}
Table 6: Numerical simulation cases with different TBM operational conditions.  
The measured torque and thrust force are considered the criteria for estimating TBM performance. Their being below the specification of the TBM signifies that more rapid tunnelling could be possible than is currently underway. That is, an increase in the penetration rate could be possible by increasing the jacking force within the capacities of the torque and thrust force. Conversely, excessive torque and thrust force represent increased risk of downtime. Therefore, the penetration rate has to be reduced to bring them within acceptable levels.  
When examining the torque data here, the raw data are modified to facilitate control of the operational conditions and comparison of varying data. Figure 9 presents the collected raw and modified torque data during 200 mm of TBM advance under the specific operational conditions of \(\omega_{cutter}\) = 2 rpm, \(PR\) = 0.5 mm/s, and \(\omega_{screw}\) = 15 rpm. The figure shows the fluctuations of the raw torque data to be so large as to hinder regulation of the operational conditions within the defined bounds. Analyzing the overlapping data for comparison is also difficult. Therefore, a moving average scheme (\(n=11\)) is adopted to adjust the raw data.  
Meanwhile, the chamber pressure and discharge of particles are assessed in terms of tunnelling safety, because they are directly related to tunnel face stability and ground settlement. Excessive chamber pressure during tunnelling will cause heaving, which is severely damaging to existing structures. Conversely, insufficient chamber pressure will lead to an abrupt soil inflow causing settlement. Therefore, in addition to the chamber pressure and discharging data, the measured surface settlement in each analysis case is compared after completion of the TBM advance.  
All analyses consider a 300 mm advance of the EPB shield. The cases with constant operational conditions are carried out for 300 s (cases 1 and 2) or 600 s (cases 3 and 4). In contrast, the analysis with automatic control of the operational conditions (case 5) has four adjustments during the 300 mm advance, which takes about 422.84 s. After an advance of 48.96 mm, the measured thrust force reaches its lower bound, and the penetration rate reaches its upper bound (2 mm/s). Next, at 164.15 mm, the chamber pressure reaches its lower bound, causing the rotational speed of the screw conveyor to reach its lower bound (2 rpm). The third adjustment comes at 255.69 mm, when the torque hits its upper bound, inducing the penetration rate to drop to 0.2 mm/s. The last adjustment at 287.87 mm is in response to the chamber pressure reaching its upper bound, causing the rotational speed of the screw conveyor to rise to 20 rpm. Finally, an advance of 300 mm is completed with  
Figure 9: Raw torque data and moving average of raw torque data during EPB shield tunnelling simulation with constant TBM operational conditions (\(\omega_{cutter}\) = 2 rpm, \(PR\) = 0.5 mm/s, and \(\omega_{screw}\) = 15 rpm).