Civil Engineering Reference
In-Depth Information
+
X
0.4
Location of center of
critical circle
=10
°
0.3
b
Y
0.2
=20
°
Tension
crack
=30
°
H
0.1
=40
°
Drained slope
0
0
10
20
30
40
50
60
70
80
90
)
Location of critical tension crack position
Slope face angle (
°
Failure through
toe of slope
Distance
X
−
3
H
−
2
H
−
H
0
H
2
H
3
H
4
H
4
H
20˚
Friction angle
=10
°
10
°
3
H
3
H
30
°
40
°
50
°
2
H
2
H
60
°
70
°
80
°
H
H
0
0
−
3
H
−
2
H
−
H
0
H
2
H
3
H
Location of center of critical circle for failure through toe
Figure 8.11
Location of critical sliding surface and critical tension crack for drained slopes.
along a circular slide path passing through the toe
of the slope. When these conditions are not satis-
fied, it is necessary to use one of the methods of
slices published by Bishop (1955), Janbu (1954),
Nonveiller (1965), Spencer (1967), Morgenstern
and Price (1965) or Sarma (1979). This section
describes in detail the simplified Bishop and Janbu
methods of stability analysis for circular failure.
(1955) and the Janbu's modified method of slices
(1954) are given in Figures 8.16 and 8.17 respect-
ively. Bishop's method assumes a circular slide
surface and that the side forces are horizontal;
the analysis satisfies vertical forces and overall
moment equilibrium. The Janbu method allows
a slide surface of any shape, and assumes the
side forces are horizontal and equal on all slices;
the analysis satisfies vertical force equilibrium.
As pointed out by Nonveiller (1965), Janbu's
method gives reasonable factors of safety when
applied to shallow slide surfaces (which are typ-
ical in rock with an angle of friction in excess
of 30
◦
8.6.1 Bishop's and Janbu's method of slices
The slope and slide surface geometries, and the
equations for the determination of the factor of
safety by the Bishop's simplified method of slices
and rockfill), but it is seriously in error
