Geoscience Reference
In-Depth Information
Figure 5.17
Sketch of planar bank failure.
where
W
t
is the weight of failure block,
C
is the soil cohesion (kPa),
φ
is the soil
friction angle (degrees),
α
is the angle of bank slope,
y
d
is the depth of tension crack
(m), and
β
is the angle of failure plane. The failure angle is determined by
tan
−
1
H
1
2
K
tc
)
β
=
H
(
1
−
tan
α
+
φ
(5.174)
with
K
tc
being the ratio of the observed tension crack depth to the bank height.
Once a mass failure is predicted (
f
s
<
1 ), the retreat distance of the bank top,
,
and the volume of the failure block,
V
f
, are determined by
H
tan
H
−
y
d
=
β
−
(5.175)
tan
α
H
2
y
d
−
H
2
tan
1
2
V
f
=
β
−
(5.176)
tan
α
Simon
et al
. (2000) proposed a more sophisticated bank stability and toe erosion
model, which considers wedge-shaped bank failures with distinct bank material layers
and user-defined bank geometry. Their model is able to incorporate the root rein-
forcement and surcharge effects of six vegetation species, including willows, grasses,
and large trees, and simulate saturated and unsaturated soil strengths, taking into
consideration the effect of pore-water pressure. The details can be found in Simon
et al
. (2000).
