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Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
to the maximum slide mass thickness of the slope (Section A in
Figure 4). The bottom of the sliding surface is taken be
consistent to the estimated fundamental period of the sliding
mass (T
s
) that is different for the clay and sand slopes.
Table 4 presents the computed numerical horizontal
displacements together with those calculated using the different
Newmark-type displacement methods. The average difference
(%) of the Newmark-type models in the median (or mean)
displacement estimation compared to the numerical
displacement is shown in Figure 5a for both sand and clay
slopes. The dispersion of the corresponding differences is
presented in Figure 5b.
Table 4. Comparison between numerical, Newmark (1965), Rathje and
Antonakos (2011) and Bray and Travasarou (2007) displacements for
sand and clayey slope materials and for outcropping accelerograms
caled at 0.7g
s
Slope
soil
material
Earthquake
code
Computed
horizontal
displacement
(m)
Average
Newmark
(m)
Rathje and
Antonakos
Median
(m)
Bray and
Travasarou
Median
(m)
cascia
0.6
0.64
0.40
0.60
kypseli
0.50
0.55
0.50
0.65
montenegro
0.90
0.70
0.37
0.42
pacoima
0.70
0.53
0.49
0.57
sturno
1.70
1.38
0.83
0.81
duzce
1.10
0.94
0.36
0.57
sand
gilroy
0.20
0.23
0.28
0.57
cascia
0.50
0.36
0.16
0.57
kypseli
0.45
0.28
0.14
0.53
montenegro
0.82
0.47
0.16
0.72
pacoima
0.62
0.35
0.19
0.79
sturno
1.40
0.90
0.25
0.71
duzce
0.85
0.48
0.16
1.16
clayey
gilroy
0.20
0.09
0.09
0.55
4 DISCUSSION- CONCLUSIONS
In general the Newmark-type analytical models predict
comparable displacements, at least in the order of magnitude,
with the exact numerical analysis. The comparison is generally
better for the sand slope case, while for the clayey more flexible
slope the divergences are amplified. In particular Bray and
Travasarou model tend to predict generally larger displacements
with respect to the numerical analysis, whereas Newmark and
Rathje and Antonakos models underpredict the corresponding
displacements.
Among the three methods, Bray and Travasarou model was
found to present the minimum average predictive error (%) in
relation to the numerical analysis for both sand and clay slope
cases. This is in line with the inherent coupled stick-slip
assumption adopted in the method that offers a conceptual
improvement over the rigid block and decoupled approaches for
modeling the physical mechanism of earthquake-induced
landslide deformation. However, Bray and Travasarou model
presents a very large dispersion in the median displacement
estimation (up to 70% for both sandy and clayey slopes). Thus,
the use of S
a
(1.5 T
s
) seems rather insufficient to fully describe
the characteristics of the seismic loading (i.e. amplitude,
frequency content and duration) for site-specific applications.
Newmark analytical approach shows the minimum
dispersion in the displacement prediction (less than 10-20%)
with respect the numerical analysis results compared to the Bray
and Travasarou and Rathje and Antonakos models. This may be
justified by the fact that Newmark analytical method uses the
entire time history to characterize the seismic loading as
opposed to the Bray and Travasarou and Rathje and Antonakos
models that use one [S
a
(1.5 T
s
)] and two (PGA, PGV) intensity
parameters respectively. As such, uncertainties associated to the
selection of the ground motion intensity parameters are lower in
the Newmark analytical approach.
Overall, the differences in the displacement prediction
between the three models are larger for the clayey slope. Thus,
the compliance of the sliding surface in relation with the way
that the frequency content of the input motion is taken or not
into account may produce some important errors to the
estimated earthquake-induced sliding displacements of slopes. It
is suggested that a better framework is deemed necessary to
account for the various uncertainties in the seismic
displacements prediction.
(b)
(a)
Figure 5. (a) Average difference (%) and (b) dispersion of the predictive
models in the median displacement estimation compared to the
corresponding numerical displacement considering nearly rigid (sand
slope) and flexible (clayey slope) sliding masses
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Chugh A.K., Stark T.D. 2006. Permanent seismic deformation analysis
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Itasca Consulting Group 2008. Inc. FLAC (Fast Lagrangian Analysis of
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