Civil Engineering Reference
In-Depth Information
N
(a)
f
s
N
(b)
f
i
s
N
(c)
f
t
N
(d)
Randomly oriented
discontinuities
Figure 2.16
Main types of block failures
in slopes, and structural geology
conditions likely to cause these failures:
(a) plane failure in rock containing
persistent joints dipping out of the slope
face, and striking parallel to the face;
(b) wedge failure on two intersecting
discontinuities; (c) toppling failure in
strong rock containing discontinuities
dipping steeply into the face; and
(d) circular failure in rock fill, very weak
rock or closely fractured rock with
randomly oriented discontinuities.
Legend
Pole concentrations
Great circle representing
face
Great circle representing
plane corresponding to centers
of pole concentrations
f
dip direction of face
s
direction of sliding
t
direction of toppling
i
dip direction,
line of intersection
in Chapters 6-9, and it is essential that the correct
analysis method be used in design.
The diagrams given in Figure 2.16 have been
simplified for the sake of clarity. In an actual rock
slope, several types of geological structures may
be present, and this may give rise to additional
types of failure. For example, in Figure 2.11, a
plane failure could occur on joint set A, while the
bedding could form a toppling failure on the same
slope.
In a typical field study in which structural
data have been plotted on stereonets, a num-
ber of significant pole concentrations may be
present. It is useful to be able to identify those
that represent potential failure planes, and to
eliminate those that represent structures that are
unlikely to be involved in slope failures. Tests for
identifying important pole concentrations have
been developed by Markland (1972) and Hocking
(1976). These tests establish the possibility of
