Geoscience Reference
In-Depth Information
Table 18.8 Guidelines for excavation and support of 10 m span rock tunnels using RMR classes (after
Bieniawski, 1989).
RMR
Excavation
Support
class
no.
Rock bolts
Shotcrete
Steel sets
Location
Length
Spacing
Location
Thickness
×
I
Full face. 3 advance
Generally no support required except spot bolting
II
Full face. 1-1.5 m
Locally. In
3 m
2.5 m
Crown
50 mm
None
×
advance. Complete
Crown with
where
support 20 m
occasional
required
from face
wire mesh
III
Top heading and
Systematic
4 m
×
1.5-2 m
Crown
50-100 mm
None
bench. 1.5-3 m
bolts with
sides
30 mm
advance in top
wire mesh
heading. Commence
in crown
support after each
blast. Complete
support 10 m
from face
IV
Top Heading and
Systematic
4-5 m
1-1.5 m
Crown
100-150 mm
Light to
×
bench 1.0-1.5 m
bolts with
sides
100 mm
medium ribs
advance in top
wire mesh
spaced 1.5 m
heading. Install
in crown
where
support
and walls
required
concurrently with
excavation, 10 m
from face
V
Multiple drifts
Systematic
5-6 m
×
1-1.5 m
Crown
150-200 mm
Medium to
0.5-1.5 m advance
bolts with
sides
150 mm
heavy ribs
in top heading.
wire mesh
face
50 mm
spaced 0.75 m
Install support
in crown
with steel
concurrently with
and walls.
lagging and
excavation.
Bolt invert
forepoling if
Shotcrete as soon
required.
as possible
Close invert
after blasting
18.9 Norwegian Q system
The Rock Mass Quality - Q values is based on a formula with the relationship
shown in the table.
The Q values are then used to predict rock support design.
Qc
=
Q
×
UCS/100.
Unconfined Compressive Strength
=
UCS.
The tables that follow are based principally on the 1974 work but with a few later
updates as proposed by Barton.
 
 
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