## 4 Model Verification
### Comparison of the Interaction Force  
The shield operation parameters obtained from field tests were processed and compared with the results from calculation mode. Some of important shield operation parameters include the total thrust, the total torque, the cutter head rotation rate, the advance rate, etc. Among them, the total thrust and the cutter head rotation rate are active control  
Figure 10: Divided stages of the field test.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Stage**} & \multirow{2}{*}{
\begin{tabular}{c} **Distance** \\ **(mm)** \\ \end{tabular} } & \multirow{2}{*}{**Advance Rate (mm/min)**} & \multirow{2}{*}{**Rotation** **Rate (rpm)**} & \multirow{2}{*}{**Rotation Direction**} & \multicolumn{2}{c}{**Thrust (kN)**} \\ \cline{3-5}  & & & & & **Maximum** & **Average** \\ \hline
1 & 150 & 8 & 1.88 & 0.8 & counter-clockwise & 1140 & 997.0 \\
2 & 150 & 8 & 3.44 & 0.5, 0.8, 1.0 & counter-clockwise & 1450 & 1220.5 \\
3 & 180 & 7 & 1.29 & 0.5 & clockwise & 1590 & 1199.6 \\
4 & 230 & 6 & 1.68 & 0.8 & clockwise & 1770 & 1446.8 \\
5 & 300 & 8 & 3.11 & 0.8 & clockwise & 1760 & 1254.6 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Shield operation parameters in different stages.  
Figure 9: The layout of the test piles.  
parameters, while the total torque and the advance rated are passive parameters, which are produced by different shield machine monitors and change with difference of geological conditions and excavation environment. Therefore, the four shield operation parameters are correlated with each other. These parameters reflect the interaction of the shield machine with the piles.  
Before starting pile cutting, the thrust and torque of the shield machine in non-cutting pile state were tested. When the shield machine was advancing at a speed of 1\(\sim\)10 mm/min on the guide rail bracket, the total thrust was nearly steady at about 900 kN and the total torque was about 400 kN\(\cdot\)m. The additional torque values of the cutter head at the starting position, midpoint position and end position of each stage were calculated and compared with field test results. Since in this test, the shield is in an open space and there is no influence of the surrounding ground environment, the total torque and total thrust of the cutter head can be obtained by adding the above two loads. In addition, penetration depth in the numerical model refers to the vertical depth from the blade edge to the cutting surface. In the field test, the penetration depth of the tools is not constant during the advance of the shield machine because the advance rate fluctuates continuously. Penetration in shield tunneling is usually calculated by dividing the advance rate by the rotation rate and it represents the advance distance of the shield machine within one revolution of the cutter head. It is a simplified approximate calculation of the true penetration of the tools and was widely used in engineering. The steadier the advance rate is, the closer the calculated penetration is to the real penetration depth of the tools. When performing model calculations, the penetration is calculated using the average advance rate for a period of time around the calculation cross-section. Calculated total torques are compared with field test results. As shown in Figure 11, the field test torque fluctuates obviously as the shield machine continues to advance. In the first and second stages, the torque increases slightly. At these two stages, the cutter head only cuts pile A and has not touched pile B. From the third stage, the torque began to increase significantly. The main reason is that the cutting condition has changed from cutting one pile to cutting two piles at the same time, which means more shield tools are involved in cutting piles. In the fourth stage and the early stage of the fifth stage, the shield torque has been at a high value of about 1300 kN\(\cdot\)m and the cutting surface width of the two piles is close to the diameter of the piles. The field test torque reached