Civil Engineering Reference
In-Depth Information
angle, weight, pore pressure and width are meas-
ured. The program SLIDE (RocScience, 2002b)
is then used to calculate the factors of safety for
the linear and non-linear shear strengths. In the
case of the non-linear strength analysis, the val-
ues of the effective normal stress on the base of
the slices, and the corresponding instantaneous
friction angle and cohesion are also calculated, as
shown in the last three columns of Table 8.1. The
calculated factors of safety estimates are
Bishop simplified method of slices for
Mohr-Coulomb shear strength
=
1.39
Janbu modified method of slices for
Mohr-Coulomb shear strength
=
1.26
Critical center for
=45
°
Bishop simplified method of slices for
non-linear shear strength
=
1.39
Note that the stability analysis of this slope
using numerical analysis methods is shown in
Section 10.4.1.
5m
8.6.4 Circular failure stability analysis
computer programs
1
0
0 0
Scale -m
2
The circular failure charts discussed in Section 8.3
provide a rapid means of carrying out stability
analyses, but are limited to simple conditions as
illustrated in the examples. More complex ana-
lyses can be carried out using the Bishop and
Janbu methods discussed in Section 8.6.3, and the
purpose of providing details on the procedures is
to show the principles of the analyses.
3
4
n
/
R
=0.401
d
/
L
=0.117
5
6
7
8
Figure 8.19
Section of sandstone slope showing water
table, slice boundaries, tension crack and the expected
circular sliding surface.
Table 8.1
Calculated shear strength values of slices using Mohr-Coulomb and Hoek-Brown failure criteria
Slice parameters for all cases
Mohr-Coulomb
values for Bishop
and Janbu analyses
Non-linear failure criterion
values for Bishop analysis
Slice
member
Angle
of slice
base, ϕ
(degrees)
Slice
height
(MN)
Pore
pressure,
γ
w
h
w
(MPa)
Slice
width
(m)
Friction
angle,
(degrees)
Cohesion,
c (MPa)
Base
effective
normal
stress,
σ
n
(MPa)
Inst.
friction
angle,
φ
i
(degrees)
Inst.
cohesion,
c
i
(MPa)
1
25
1.312
0.017
6.1
43
0.145
0.139
53.8
0.068
2
29
1.597
0.047
6.1
43
0.145
0.169
53.8
0.068
3
34
2.603
0.071
6.1
43
0.145
0.270
49.8
0.096
4
39
2.635
0.087
6.1
43
0.145
0.261
51.3
0.085
5
44
3.501
0.095
6.1
43
0.145
0.323
49.0
0.104
6
50
3.914
0.087
6.1
43
0.145
0.324
48.6
0.107
7
57
3.592
0.047
6.1
43
0.145
0.240
50.3
0.092
8
65
2.677
0
6.1
43
0.145
0.109
54.5
0.064
