1. The fabrication and installation of shield base, reaction frame and axial support of upper segment should have sufficient rigidity to ensure that the deformation after loading meets the requirements of shield tunneling direction.
2. When installing the shield base and reaction frame, ensure that the direction of shield tunneling is consistent with the tunnel design axis.
3. Because the roundness of the temporary segment (negative ring segment) directly affects the segment assembly accuracy during shield tunneling, it is necessary to ensure its roundness when installing the temporary segment, and take measures to prevent its rotation, radial displacement and opening deformation (the temporary segment usually does not form a closed loop when installing, and there is a transportation channel on its upper part).
4. Before removing the enclosure structure of the portal, confirm the reinforcement effect of the soil at the portal, and grout it when necessary to ensure that the soil will not collapse, the ground deformation will not be too large, and the excavation surface will be stable during the shield launching process.
5. Because the jack on the upper part of the shield cannot be used before assembling the last temporary segment (negative loop and closed loop) (the temporary segment installed before assembling the last temporary segment is usually open loop), it is necessary to drive slowly during the process of the shield entering the soil layer and passing through the soil reinforcement section to reduce the thrust of the jack and make the direction of the shield easy to control. When the shield reaches the middle of the soil reinforcement section at the entrance, the set pressure of the earth pressure bin (mud bin) increases gradually.
6. Usually, after the shield tail of the shield machine enters the hole, the whole circle of temporary segment (negative ring) is assembled, and axial support is installed at the opening, so that all shield jacks can be used in subsequent shield tunneling.
7. After the shield tail of the shield machine enters the hole, seal the hole and tightly close the closed-loop segment to prevent mud and grouting slurry from leaking from the hole.
8. Strengthen the observation of formation deformation around the working well, deformation and displacement of shield base, reaction frame, temporary segment and upper axial support of segment. When it exceeds the predetermined value, effective measures must be taken before the excavation can continue.
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