Civil Engineering Reference
In-Depth Information
(a)
(b)
Face
Line of
intersection
N
Plane A
Wedge
Plane B
Face
i
Direction of
sliding
fi
i
Note: The convention adopted in this
analysis is that the flatter plane is always
referred to as Plane A.
N
(c)
(d)
Plane A
Line of intersection
Plane B
Plane B
Face
i
Plane A
i
fi
i
Range of
i
for sliding
Figure 7.3
Geometric conditions for wedge failure: (a) pictorial view of wedge failure; (b) stereoplot showing
the orientation of the line of intersection, and the range of the plunge of the line of intersection
ψ
i
where failure
is feasible; (c) view of slope at right angles to the line of intersection; (d) stereonet showing the range in the
trend of the line of intersection
α
i
where wedge failure is feasible.
intersection is represented by the point where
the two great circles of the planes intersect,
and the orientation of the line is defined by its
trend
(α
i
)
and its plunge
(ψ
i
)
(Figure 7.3(b)).
dip direction of the line of intersection were
the same as the dip direction of the slope face.
3
The line of intersection must dip in a direction
out of the face for sliding to be feasible; the
possible range in the trend of the line of inter-
section is between
α
i
and
α
i
(Figure 7.3(d)).
2
The plunge of the line of intersection must be
flatter than the dip of the face, and steeper
than the average friction angle of the two slide
planes, that is
ψ
fi
>ψ
i
>φ
(Figure 7.3(b)
and (c)). The inclination of the slope face
ψ
fi
is
measured in the view at right angles to the line
of intersection. Note the
ψ
fi
would only be the
same as
ψ
f
, the true dip of the slope face, if the
In general, sliding may occur if the intersec-
tion point between the two great circles of the
sliding planes lies within the shaded area on
Figure 7.3(b). That is, the stereonet will show if
wedge failure is kinematically feasible. However,
