## 5 Conclusions  
In this paper, based on the project of cross passage in Suzhou Metro Line 11, the finite element method is employed to analyze the mechanical response when the flat-face cutterhead is used to open the portal at the main tunnel. The following conclusions can be drawn.  
1. Among the six rings of segments at the connection part, the maximum vertical displacement caused by cutting mainly concentrates on the top of the fully cut ring. The maximum horizontal displacement appears at the waist on the side of the tunnel portal of the semi-cut ring. The maximum displacement of the segment ring appears after the formation of the third stage, and the position is at the waist of the tunnel entrance. This is mainly caused by the jacking of the plane cutter head during excavation. The maximum displacement value of 6.453 mm and 6.223 mm are under the allowable value in the Chinese code for monitoring measurement of urban rail transit engineering (30 mm) [18].
2. From the displacement of the measuring points. With the pushing of the cutterhead of the shield tunneling machine, due to the disturbance of the cutterhead and the extrusion of external earth pressure, the upper and lower parts of the segment in contact with the tunnel portal undergo significant displacements in the horizontal and vertical directions. Moreover, the displacement increases steadily over time and then stabilizes to about after the formation of the portal. The end of the segment on the waist side of the tunnel in contact with the tunnel portal only experiences a substantial displacement in the horizontal direction, while the displacement in the vertical direction is not significant, with a value of about 1 mm.
3. Alongside the direction of the main tunnel, the displacement of the middle four rings increases consistently with the process of cutting, with the maximum of exceeding 6 mm. The existence of the pre-support system effectively controls the displacement of the third and fourth fully cut rings. It is suggested that the soil near the second to fifth ring should be reinforced with emphasis.
4. When using the flat-face cutterhead to open the portal, in four different stages, the stress distribution in the segment is not uniform. The stress changes are more regular, and the maximum stress occurs in stage I. Although the maximum stress response value of the segment is large, it is not sufficient to cause damage to the concrete and result in the formation of cracks in the segment.
5. The pattern of bending moment variation is more pronounced in the segment rings. As the cutterhead keeps advancing, the bending moment inside the segment ring within the range of 45\({}^{\circ}\) above and below the arch waist first decreases and then increases. It has been verified that the support system optimized the structural stress state. On the other hand, after the upper and lower parts of the tunnel are drilled through, the load is gradually taken up by the semi-cut ring, and the bending moment of the semi-cut ring after the third stage is larger than that of the fully cut ring.  
Conceptualization, S.L. and X.L.; methodology, B.L. and X.L.; software, B.L.; validation, B.L.; writing--original draft preparation, B.L. and X.L.; writing--review and editing, X.L. and S.L. All authors have read and agreed to the published version of the manuscript.  
This research was funded by Suzhou Science and Technology Plan (Basic Research) Project (No. SJC2023002) and Open Fund of Jiangsu Urban Underground Space Development and Utilization and Safety Protection Engineering Research Center (No. 2023-CSDXJJ-01).  
Not applicable.  
The original contributions presented in the study are included in the article, further inquiries can be directed to the corresponding author.  
Author [PERSON] and [PERSON] were employed by the company Zhongyi-ifeng Construction Group Co., Ltd. The remaining authors declare that the re-search was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.