Circular steel beams that are erected to support the tunnel where the rock is not self supporting, otherwise known as “bad ground”.

Special (high alloy) steel plates mounted on the cutterhead that are designed to withstand high abrasion.

A horizontal entrance to an underground excavation site.

The structure usually mounted on the TBM Back-Up in a conveyor muck removal system. The structure includes a tail pulley and protected working window mounted on hydraulic actuators so that idler assemblies can be installed while the belt is still moving.

A surface mounted pipe-jacking unit used to bore small diameter (2.0 m and under) drives. The machine can bore and line a variety of ground conditions based on the cutting head attachment. Muck is removed by means of a rotating auger.

A cutterhead that allows cutters to be changed and inspected from behind or in front of the cutterhead. It is used as a safer alternative to the front loading cutterhead.

A TBM support system that trails the TBM and contains all the tunneling accessories and support equipment including the TBM power unit. It also allows for muck transport via conveyor systems or muck cars.

A mechanized unit used to add more belt to the continuous conveyor system as the tunnel gets longer. Can be placed either underground or on the surface.

A storage system for the conveyor belt which pays out the belt as the TBM bores, allowing continuous TBM advance. Belt tension is maintained by tensioned rollers on the cassette, which retract to be closer as the conveyor extends.

A drive that allows power to be added to a conveyor belt at specific locations on the conveyor system as the tunnel advances.