Term/Expression
Description
Chainage or station
The cumulative distance along the centreline,
frequently but not always starting at zero.
Design Profile
Geometric description of the designed shape
of the cross-section of the tunnel. The
design profile can contain straight or curve
elements.
Excavated Profile
Shape of the cross-section of the tunnel that
has been excavated.
Underbreak
When the excavated profile is inside the
design profile, the underbreak is the perpen-
dicular distance between the design profile
and the excavated profile.
Overbreak
When the excavated profile is outside of the
design profile, the overbreak is the perpen-
dicular distance between the design profile
and the excavated profile.
Tunnel Portal
The open end of a tunnel.
Tunnel Face
The point where the excavated tunnel meets
existing terrain.
Superelevation (Rotation)
Angle of rotation of a design profile. Used to
take into account the velocity of a moving
vehicle through a curve.
Rotation Point
The point about which the design profile is
rotated. This point may or may not coincide
with the centreline.
g
h
f
e
d
c
b
a
Tunnel_001
a
Centreline
b
Centreline offset
c
Point on design profile
d
Centreline height offset
e
Design profile
f
Excavated profile
g
Underbreak
h
Overbreak
b
a
c
Tunnel_002
a
Centreline or axis
b
Tunnel portal
c
Tunnel face
General terms
3D View
Roads - General
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