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residential
landscaping and
irrigation. As
a result of the
post-grading
soil wetting
and expansion
in conjunction
with the upslope
topographic
confinement
and lack of
confinement
downslope, the
model predicted
stress levels and
displacement
patterns that were consistent with
the observed conditions. The model
provided a basis for predicting the
maximum amount of ground move-
ment that could be anticipated and
confirmed the factor of safety against
gross instability remained relatively
high.
In both of the cases outlined above,
analytical and/or physical models were
developed and utilized to evaluate
monitoring results that could not be
readily understood or explained with-
out the use of those models. The use
of this type of modeling has proven
useful in the evaluation of data from
monitoring programs on many occa-
sions.
Glenn D. Tofani,
Principal Engineer
GeoKinetics
77 Bunsen, Irvine, California 92618
Tel: (949) 502-5353
E-mail:
Figure 6. Cross section through Keller Ridge Landslide.
recorded by the inclinometers. Where
the ancient landslide debris had been
left in place, the movement occurred
along the basal rupture surface.
Downslope of the slide debris, the
movement generally occurred as a
dispersed zone of deformation within
the fill without any well defined
offsets. The monitoring results and
crack patterns indicated the amount
movement increased in the downsl
direction. Piezometers were also
installed within the development to
delineate groundwater levels. The
effective shear strength parameters
for the landslide rupture surface we
relatively well defined by back-cal
lations based upon a factor of safet
of unity prior to grading. The shear
strength parameters for the fill soils
were based upon a large number of
tests that had been performed on th
material. Slope stability calculation
using all of the available data for th
post-graded condition yielded fac-
tors of safety in excess of 1.5. Thos
results appeared to be inconsistent
with the fact that several inches of
movement had occurred along the
basal rupture surface. A finite ele-
ment model of the site was created
more thoroughly evaluate the induc
stresses and deformation. This mod
incorporated the shrink-swell chara
teristics of the expansive fill soils a
simulated the post-grading wetting
that had occurred as a result of the