Editing Tunnel boring machine (section)

=== Tunnel wall types ===

==== Concrete lining ====

[[File:Hydraulic jacks holding a TBM in place.jpg|thumb|Hydraulic jacks holding a TBM in place]]

Shielded TBMs are typically used to excavate tunnels in soil. They erect concrete segments behind the TBM to support the tunnel walls.{{sfn|Stack|1995}}{{page needed|date=April 2025}}

The machine stabilizes itself in the tunnel with hydraulic cylinders that press against the shield, allowing the TBM to apply pressure at the tunnel face.

==== Main Beam ====
Main Beam machines do not install concrete segments behind the cutter head. Instead, the rock is held up using ground support methods such as ring beams, rock bolts, [[shotcrete]], steel straps, ring steel and wire mesh.{{sfn|Stack|1995}}{{page needed|date=April 2025}}