Eye

The opening in the shaft wall through which the MTBM is launched.

Fabric

Used to describe the physical material from which a pipe is made: vitrified clay; brick; concrete, for example.

Face

The location where excavation is taking place.

Face Access

Access to the location where excavation is taking place, typically through the cutting chamber. MTBM configuration may only allow limited personnel access to the back of the cutter wheel from within the pipe string. An airlock may also be required in the rear of the MTBM to maintain air pressure for counterbalancing earth and groundwater pressures.

Face Pressure

Earth and groundwater pressures applied against the cross-sectional area of the microtunnel face.