Engineering geology aspects for design and classification - Tunnel Engineering: Basics and Additional Services for Design and Construction - page 91

Table 2-34 Determination of the excavation classes due to the excavation support for TBM tunnelling
in solid rock 1) .

Class I Class II Class III Class IV Class V Class T

Excavation classes for tunnels
Machine
area
L1

≤ n anchors
around tunnel
perimeter

> n anchors
around tunnel
perimeter with
mesh and/or
lagging sheets

Anchor with
mesh and
partial arch
Shotcrete
as sealing
around > 1/4
of the profile
perimeter
Pressure-
distributing
elements at the
bracing shoes

Closed steel
sets with
or without
lagging
Full-surface
steel elements

Closed
segment
installation

Backup
area
L2

Mesh as
rockfall
support,
fixed with
anchors or
bolts
Invert
segments
in case
provided
in design
for all rock
classes

Systematic
arrangement
> n anchors
with partial
arch around
> 1/4 of the
profile peri-
meter
Mesh, shotcre-
te around < 1/2
of the profile
perimeter
Non-system-
atic arrange-
ment
> n anchors

Systematic
arrangement
Mesh, shotcre-
te around the
entire profile
perimeter
except invert
Partial arches
with anchors
around ≤ 3/4
of the profile
perimeter
Non-system-
atic arrange-
ment
Mesh,
shotcrete
around ≤ 1/2
of the profile
perimeter
> n anchors
with partial
arches around
< 1/4 of the
profile peri-
meter

Systematic
arrangement
Invert support
with shotcrete,
if no invert
segments are
provided
Closed steel
sets, possible
supported
on invert
segments
Non-system-
atic arrange-
ment
Mesh, shotcre-
te around the
entire profile
perimeter
except invert
Partial arches
with anchors
around ≤ 3/4
of the profile
perimeter
Closed steel
sets with or
with out lagging

Rearward
area L3 up
to 200 m
behind
backup

Excavation support in L3 is insignificant for the assignment of excavation classes.
In case such support is intended, waiting time items are to be provided.

values for n max. excavation diameter: 4.00 m 6.00 m 9.00 m 12.00 m

(number of anchors per
running m of tunnel) n 2 3 4 6
1) If there is more than one support measure in a field of the table, each measure alone is sufficient for
classification.