Environmental Engineering Reference
In-Depth Information
(b) For intact rock m
i
. These should preferably be measured from triax-
ial tests on intact rock samples. Alternatively an approximation can be made using the
uniaxial compressive strength
m
i
and
ci
and tensile strength
ti
of the intact rock and the
equations below.
ci
m
i
(16.11)
ti
1.2
1 p
m
7
(16.12)
0.4
i
i
The estimation of m
b
,
b
and s
b
can be made using the following equations:
GSI
100
2.5
m
i
(16.13)
m
i imum of
b
75
30m
m
b
(0.9
)exp
(16.14)
b
i
i
i
GSI
85
exp
15
s
i imum of
(16.15)
b
1
where GSI
expotential.
Douglas (2003) indicates that the equations below from Hoek et al. (2002) can be used
to estimate the cohesion,
c
Geological Strength Index, exp.
n
, and friction angle,
, of the rock mass by developing a
versus
plot for the relevant stress conditions and rock properties using equations 16.16,
16.17 and 16.18.
d/d
1
1
3
1
3
1
3
(16.16)
.
n
2
2
d/d
1
1
3
d/d
d/d
1
3
(
)
(16.17)
1
3
1
1
3
d/d
1
m(m /
)
(1)
(16.18)
3
3
b
b
3
ci
where d
3
plot.
They note that these equations replace those in Balmer (1952), which Douglas (2003)
indicates were incorrect.
1
/d
3
is the slope of the
1
, versus
