Geoscience Reference
In-Depth Information
- Squeezing loads in plastic incompetent rock, and
- Rock stresses in competent rock.
•
Major and minor principal stresses
σ
1
and
σ
3
.
18.15 Selecting safety level using the Q system
•
The excavation support ratio (ESR) relates the intended use of the excavation to
the degree of support system required for the stability of the excavation.
Table 18.15
Recommended ESR for selecting safety level (Barton et al., 1974
with subsequent modifications).
Type of excavation
ESR
Temporary mine openings
2-5
Permanent mine openings, water tunnels for
1.6-2.0
hydropower, pilot tunnels
Storage caverns, water treatment plants, minor
1.2-1.3
road and railway tunnels, access tunnels
Power stations, major road and railway tunnels,
0.9-1.1
portals, intersections
Underground nuclear power stations, railway
0.5-0.8
stations, sport and public facilities, factories
18.16 Support requirements using the Q system
•
The stability and support requirements are based on the Equivalent Dimension
(D
e
) of the excavation.
•
D
e
=
Excavation Span, diameter or height/ESR.
Table 18.16
Support and no support requirements based on equivalent dimension
relationship to the Q value (adapted from Barton et al., 1974).
Q value
Equivalent dimension (D
e
)
Comments
0.001
0.17
Support is required above the D
e
0.01
0.4
value shown. No support is required
0.1
0.9
below that value. The detailed
1
2.2
graph provides design guidance on
10
5.2
bolts spacing and length, and
100
14
concrete thickness requirements
1000
30
18.17 Prediction of support requirements using Q values
•
Additional details as extracted from Barton's 2006 graphs are presented below.
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