2240
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
3.3
Reduction factor of the soil shear strength
A quantitative assessment of the relationships between different
factors (i.e. slope angle, failure depth and water table depth) and
reduction factor of soil shear strength due to earthquake was
performed. Figure 5 shows the areal distribution of the reduc-
tion factor of the soil shear strength considering a rainfall inten-
sity of 120 mm a day. The bedrock is assumed to be much less
permeable than the soil cover. Soil depth varies from 4 to 7 m
depending on the type of soil and topographic characteristics in-
side the virtual region.
For this reason, a model that includes the reduction of the
soil strength parameters induced by the strong motion of an
earthquake was developed and implemented. A virtual case
study was performed to assess the behavior of the model and its
parameters. This was achieved by calculating two reduction fac-
tors that represented the reduction of rainfall threshold in space
and time, and the reduction of the soil strength due to prevailing
conditions.
There are still some limitations regarding the model and fur-
ther validation needs to be done. A thorough calibration of the
reduction factors should be done locally and the possibility of
using real events that are well documented should be consid-
ered. However, despite its limitations, the model provides a
practical approach to assess the prospective outcomes of future
hazards and their interactions. Thus the model contributes to in-
creasing the knowledge required for the protection of the people
at risk and their assets.
5 ACKNOWLEDGEMENTS
The research leading to these results has received funding from
the European Community’s Seventh Framework Programme
[FP7/2007-2013] under Grant Agreement No 265138 New
Multi-HAzard and MulTi-RIsK Assessment MethodS for
Europe (MATRIX).
Fig. 5 Spatial distribution of the soil shear strength reduction factor
(fr).
6 REFERENCES
3.4
Slope stability assessment including the reduction factors
A two dimensional equilibrium stability analysis based on the
infinite slope model was carried out in order to compute the
new factors of safety that included the reduction factors. The
mean values of the logarithmic distributions functions of the in-
put parameters were applied in the analyses. A constant porosity
of 42% and an evapotranspiration of 5 mm/day were selected
throughout the area. Five different friction angles were used for
the different soil types: 30, 32, 34, 36, 38°. Figure 6 shows the
results of the stability analysis considering the reduction of the
soil strength after an earthquake.
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Fig. 6 Stability analysis considering the loss of strength of soil due to the
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4 CONCLUSIONS
A natural system is not just the sum of its components but is the
result of many interacting parts. Hence, a multi-hazard assess-
ment should address evolving characteristics in space and time.
These characteristics can, for analysis purposes, be analyzed as
the alteration of the susceptibility and the triggering mechanism.
A multi-hazard assessment offers the advantage to consider a
slightly larger part of the overall system. The major challenge is
to identify the relationships among the interacting factors and
establish the respective links.
