A segment erector is the robotic lifting system inside the rear shield of a Tunnel Boring Machine, or TBM. Its job is to place heavy curved precast concrete segments into a circular tunnel lining ring. This ring supports the ground after excavation and creates the finished tunnel wall.
Without accurate segment erection, the tunnel could leak, deform, or become misaligned.
Key Facts
- Weight force of a segment: W = mg
- Lifting torque about the erector axis: τ = rF
- A full tunnel ring is made from several curved segments plus often a smaller key segment.
- The erector uses hydraulic or electric actuators to lift, rotate, and position each segment.
- Segment placement must match the ring geometry so the lining stays circular and centered.
- TBM thrust jacks push on the completed ring to move the machine forward.
Vocabulary
- Segment erector
- A mechanical arm inside a TBM that lifts and positions precast lining segments to form a tunnel ring.
- Tunnel lining segment
- A curved precast concrete piece that becomes part of the permanent tunnel wall.
- Rear shield
- The back section of a TBM shield where the tunnel lining is assembled behind the cutting face.
- Key segment
- The final segment inserted into a ring to lock the other segments into position.
- Thrust jack
- A hydraulic cylinder that pushes against the completed lining ring to drive the TBM forward.
Common Mistakes to Avoid
- Treating each segment as a flat block is wrong because lining segments are curved to match the circular tunnel shape.
- Ignoring the segment weight is wrong because the erector must supply enough force and torque to lift and rotate a heavy concrete piece safely.
- Assuming the ring supports itself before closure is wrong because the segments need correct sequencing and the key segment to complete the stable circular ring.
- Confusing excavation with lining installation is wrong because the cutterhead removes ground while the segment erector builds the tunnel wall behind it.
Practice Questions
- 1 A concrete lining segment has a mass of 3200 kg. Using g = 9.8 m/s², calculate its weight in newtons.
- 2 An erector holds a segment with a weight of 31,000 N at a distance of 1.2 m from its rotation axis. Calculate the lifting torque needed, ignoring friction.
- 3 Explain why a TBM must install lining segments soon after excavation instead of waiting until the whole tunnel is bored.