The segment bolt of subway is a special fastener used by shield tunneling machine to connect and fasten its segments during the tunneling process. Through the connection of these bolts, several arch segments can be connected into a circle, which can support the whole tunnel surface. It is also called segment bolt, even a segment connector, or it is specially used for shield tunnel, so it is called segment bolt or connector of shield tunnel.

The segment bolts are divided into circumferential and longitudinal. Some designs have the same circumferential and longitudinal specifications. Some designs adopt two specifications, even two strength grades, in the circumferential and longitudinal directions. Generally speaking, the length of the circumferential segment bolt is longer than that of the longitudinal segment bolt.

In the tunnel construction, a machine which is used for starting and driving is called shield machine, which has the functions of excavating and cutting soil, transporting soil ballast and assembling tunnel lining; However, shield machine is assembled with several segments when lining the tunnel. A screw is used to connect and fasten the pipe, and the pipe is assembled to form a circular column shape, and the segment is a cylindrical wall; During excavation, the ground settlement can be controlled, the influence on the ground buildings can be reduced and the water surface traffic is not affected during underwater excavation. The segments are combined to form a pipe. This design is a straight or arc shaped fastening connection, namely segment bolts. The segment bolts are divided into circumferential and longitudinal. Some designs have the same circumferential and longitudinal specifications. Some designs adopt two specifications, even two strength grades, in the circumferential and longitudinal directions. Generally speaking, the length of the circumferential segment bolt is longer than that of the longitudinal segment bolt.

Grade and material

Segment bolts are designed to be of different strength grades according to the application environment and different stress conditions, as other bolts and fasteners.

The common ones are: grade 5.8, level 6.8 and level 8.8.

The corresponding production materials are: Q235, 45 × steel, 40Cr, etc.

Surface treatment of segment bolts

surface treatment

The common surface treatment of segment bolts are: hot dip galvanizing (hot dip galvanizing), Dacromet (commonly known as zinc based chromate), powder zinc, multi-component composite powder zinc. The surface treatment of segment bolts is very important. Because the segment bolts are installed underground, they play the role of connecting the segments. It is located in a humid environment, which can easily cause corrosion of bolts and rust. Therefore, if the surface treatment of the bolt fails to meet the design requirements, it will cause the bolt to rust in the process of use, and the corrosion inside the bolt will affect the mechanical properties and tensile strength of the bolt.