Civil Engineering Reference
In-Depth Information
(a)
R
Vertical
slice
E
i
-1
i
-1
h
i
-1
W
i
b
i
h
i
E
i
A
i
S
=
(
c
i
+
i
tan
i
)A
i
FS
i
A
i
Circular sliding
surface
Forces acting on slice,
i
(b)
Non-circular
sliding surface
Figure 8.2
The shape of
typical sliding surfaces:
(a) large radius circular
surface in homogeneous,
weak material, with the detail
of forces on slice;
(b) non-circular surface in
weak, surficial material with
stronger rock at base.
necessary to use a procedure that allows the shape
of the surface to be defined.
For each combination of slope parameters there
will be a slide surface for which the factor of
safety is a minimum—this is usually termed the
“critical surface.” The procedure to find the
critical surface is to run a large number of ana-
lyses in which the center co-ordinates and the
radius of the circle are varied until the surface
with the lowest factor of safety is found. This
is an essential part of circular slope stability
analysis.
8.2.2 Stability analysis procedure
The stability analysis of circular failure is carried
out using the limit equilibrium procedure similar
to that described in earlier chapters for plane and
wedge failures. This procedure involves compar-
ing the available shear strength along the sliding
surface with the force required to maintain the
slope in equilibrium.
The application of this procedure to circu-
lar failures involves division of the slope into a
series of slices that are usually vertical, but may
