Geoscience Reference
In-Depth Information
Table 18.23
Average cohesive and frictional strength using Q value (adapted from Barton, 2006).
Strength
Relationship
Relevance
component
Cohesive
CC
=
(RQD/J
n
)
×
(1/SRF)
×
(UCS/100)
Component of rock mass requiring
strength
concrete, shotcrete or mesh support.
(CC)
Frictional
FC
tan
−
1
(J
r
/J
a
)
(J
w
)
Component of rock mass requiring
=
×
strength
bolting.
(FC)
•
The Geological Strength Index (GSI) was introduced by Hoek et al. (1995) to
allow for the rock mass strength of different geological settings. The GSI can be
related to rock mass rating systems such as the RMR or Q systems.
18.24 Prediction of strength and material parameters using
Q Values
•
The interrelationship between the Q values and the various parameters provide
the following values.
Table 18.24
Typical strength values using Q value (adapted from Barton, 2006).
RQD
Q
UCS
Qc
Cohesive strength
Frictional
V
p
E
m
ass
(MPa)
(CC) (MPa)
Strength (FC)
◦
(km/s)
(GPa)
100
100
100
100
50
63
5.5
46
90
10
100
10
10
45
4.5
22
60
2.5
55
1.2
2.5
26
3.6
10.7
30
0.13
33
0.04
0.26
9
2.1
3.5
10
0.008
10
0.0008
0.01
5
0.4
0.9
18.25 Prediction of deformation and closure using Q values
•
Barton used the Q value to estimate the rock deformation based on the relation-
ships shown in the Table below.
Table 18.25
Typical deformation and closure using Q value (adapted from Barton, 2006).
Movement
Relationship
Deformation,
(mm)
Span (m)/Q
=
×
√
(
Vertical deformation,
=
Span (m)/(100 Q)
σ
v
/UCS)
v
v
×
√
(
Horizontal deformation,
Height (m)/(100 Q)
h
/UCS)
=
σ
h
h
At Rest pressure, K
o
K
o
Span (m)/Height (m)
2
(
h
/
v
)
2
=
×
Search WWH ::
Custom Search