## 4 Analysis of Factors Influencing Segment Fracture Width
### Influence of Nonuniform Distribution of Cylinder Pressure on the Fracture Width of a Segment  
When the shield machine turns, the distribution of cylinder pressure needs to be adjusted. For example, when the shield machine makes a left turn, the extension of the cylinder in the left partition will be appropriately reduced, and the extension of the cylinder in the right partition will be increased, which corresponds to the reduction in the thrust of the cylinder in the left partition and the increase in the thrust of the cylinder in the right partition. The loading model diagram is shown in Figure 18. The red part is where the cylinder is loaded. This section analyzes the influence of uneven cylinder pressure distribution on segment fracture  
Figure 17: Numerical simulation of fracture width at different inclination angles.  
Figure 18: The left and right side partitions control 4 grippers, respectively.  
Due to the action of gravity, the thrust force received by the lower five grippers is 1.5 times that of the other grippers. When the total thrust is 16,000 kN, the stress exerted by the lower five grippers on the segment is 12.975 MPa, and the stress exerted by the upper three grippers on the segment is 8.65 MPa. When the increase or decrease in the loading of the left and right four grippers is adjusted to 50%, the stress exerted on the segment by the four grippers on the left is 4.325 MPa, while the stress exerted on the segment by the four grippers on the right is 12.975 MPa. The equivalent crack width of the segment is 0.23 mm, which exceeds the standard limit value, as shown in Figure 19a.  
When the total thrust is 17,000 kN, the stress exerted on the segment by the lower five grippers is 13.785 MPa, and the stress exerted on the segment by the upper three grippers is 9.19 MPa. When the increase or decrease in the loading of the left and right four grippers is adjusted to 40%, the stress exerted on the segment is 5.514 MPa. The stress exerted on the segment by the four grippers on the right is 12.866 MPa, and the equivalent crack width of the segment is 0.20 mm, reaching the standard limit value, as shown in Figure 19b.  
When the total thrust is 18,000 kN, the stress exerted on the segment by the lower five grippers is 14.596 MPa, and the stress exerted on the segment by the upper three grippers is 9.73 MPa. When the increase or decrease in the loading of the left and right four grippers is adjusted to 35%, the stress exerted on the segment is 6.325 MPa. The stress exerted on the segment by the four grippers on the right is 13.136 MPa, and the equivalent crack width of the segment is 0.20 mm, which has exceeded the standard limit value, as shown in Figure 19c.  
When the total thrust is 19,000 kN, the stress exerted on the segment by the bottom five grippers is 15.41 MPa, and the stress exerted on the segment by the top three grippers is 10.27 MPa. When the increase or decrease in the loading of the left and right four grippers is adjusted to 30%, the stress exerted on the segment by the four grippers on the right is 13.351 MPa, and the equivalent crack width of the segment is 0.21 mm, which has exceeded the standard limit value, as shown in Figure 19d.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Total Thrust (kN)** & **Left** & **Right** & **Equivalent Fracture Width (mm)** \\ \hline \multirow{4}{*}{16,000} & \(-\)10\% & +10\% & 0.11 \\  & \(-\)20\% & +20\% & 0.12 \\  & \(-\)30\% & +30\% & 0.13 \\  & \(-\)50\% & +50\% & 0.23 \\  & \(-\)10\% & +10\% & 0.12 \\  & \(-\)20\% & +20\% & 0.13 \\  & \(-\)30\% & +30\% & 0.14 \\  & \(-\)40\% & +40\% & 0.20 \\  & \(-\)10\% & +10\% & 0.12 \\
18,000 & \(-\)20\% & +20\% & 0.14 \\  & \(-\)30\% & +30\% & 0.15 \\  & \(-\)35\% & +35\% & 0.20 \\  & \(-\)10\% & +10\% & 0.13 \\
19,000 & \(-\)20\% & +20\% & 0.15 \\  & \(-\)30\% & +30\% & 0.21 \\ \hline \hline \end{tabular}
\end{table}
Table 6: The simulation value of segment fracture width under the change of loading amplitude of the left and right 4 grippers.  
Figure 19: _Cont._