Civil Engineering Reference
In-Depth Information
0
.01
.02
.03
.04
2.0
.05
.06
.07
.08
.09
.10
.11
.12
.13
.14
.1
.1
.1
.1
.1
.20
1.8
1.6
c
H
tan
1.4
1.2
.25
tan
FS
.30
90
°
1.0
.35
.40
.45
.50
60
.70
.80
.90
1.0
1.5
2.0
4.0
8
0.8
Slope angle
80
°
0.6
70
°
60
°
50
°
0.4
40
°
30
°
20
°
0.2
10
°
0
0
.02
.04
.06
.08
.10
.12
.14
.16
.18
.20
.22
.24
.26
.28
.30
.32
.34
c
H
FS
Figure 8.7
Circular failure chart number 2—ground water condition 2 (Figure 8.5).
Because of the speed and simplicity of using
these charts, they are ideal for checking the sens-
itivity of the factor of safety of a slope to a wide
range of conditions. For example, if the cohesion
were to be halved to 20 kPa and the ground water
pressure increased to that represented by chart
number 2, the factor of safety drops to 1.28.
were determined for each slope analyzed. These
locations are presented, in the form of charts, in
Figures 8.11 and 8.12.
It was found that, once ground water is present
in the slope, the locations of the critical circle and
the tension crack are not particularly sensitive to
the position of the phreatic surface and hence only
one case, that for chart number 3, has been plot-
ted. It will be noted that the location of the critical
circle center given in Figure 8.12 differs signific-
antly from that for the drained slope plotted in
Figure 8.11.
These charts are useful for the construction of
drawings of potential slides and for estimating
the friction angle when back-analyzing existing
8.4 Location of critical slide surface
and tension crack
During the production of the circular failure
charts presented in this chapter, the locations
of both the critical slide surface and the critical
tension crack for limiting equilibrium
(
FS
=
1
)
