Components of Tunnel

Chainage

The length along the longitudinal direction of tunnel

Crown

The top portion of tunnel is crown. It can be circular,semi-circular or rectangular in shape.

Side/Wall

The side portion of tunnel. It is generally vertical.

Bench

The bottom part of tunnel left after the excavation of heading is said to be bench. Excavation of face in done in multiple step for large cross sectional area.

Invert

The lower portion of tunnel

Portal

The entrance of tunnel is portal. Heavy support should be provided in portal.

Face

The cross sectional of tunnel where excavation is running.

Heap

The excavated material collected at the base of tunnel after blasting of tunnel face