Environmental Engineering Reference
In-Depth Information
3.2
FEM
The finite element modelling was performed using
the same geotechnical conceptual model and elas-
tic and elasto-plastic properties as for the FDM
analysis.
The results are generally in agreement with
those of finite difference modelling, and show that
the models with three or four units (including cl)
are comparable as regards displacement and strain
pattern. Displacements are concentrated along the
eastern flank and both the topographic gradient
and the geometry of hP control their direction
shear strain are recorded at the contact hP/Flcl,
critical surfaces developed. The effect of magmatic
pressures mostly affects the eastern flank, and the
maximum horizontal displacements are recorded
in the Flcl unit. The presence of the clay unit
amplifies the effect of magma pressure. no slid-
ing surfaces develop in the clay horizon neither at
depth.
The results show that the geotechnical parameters
describing the behaviour of the units, as well as their
geometries in the model, can be considered realistic
and reliable. a 3-D model is ongoing, taking into
account the validity of these assumptions and the
obtained results.
acknoWleDGMenTs
This work was funded by Dipartimento Protezione
civile (DPc)—inGV grants to T. apuani (project
V4-Flank, RU 02), and was performed in the
framework of the ilP project “new tectonic
causes of volcano failure and possible premoni-
tory signals”.
ReFeRences
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acocella, V., Behncke, B., neri, M., D'amico, s.,
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4
conclUsions
allowing for the assumptions for the stress field
initialization and the assigned elastic-plastic prop-
erties reasonable at depth in absence of direct
investigations, the stress-strain analyses show that:
1. the stepped geometry of the contact between the
hyblean Plateau and the apennine-Magrebian
chain flysh conditions the stress field. Moreover,
assuming low elastic moduli for the volcanic and
flysh units and a very stiff hyblean Plateau, it is
possible to evidence a shear strain concentra-
tion along the prosecution of the steps in agree-
ment with the Timpe structural lineaments.
2. gravity alone is not sufficient to develop deep-
seated instabilities. Plasticity states are reached
only in correspondence of high-angle surfaces
below the crater zone, creating favourable con-
ditions for magma rising.
Magmatic pressure emphasize this tendency,
highlighting superficial displacements, but they do
not seem to worsen the plasticity field at depth.
comparing the results of deformation moni-
toring and the presented models, it can be argued
that the deformation mechanisms of the eastern
flank of etna are surely controlled by magmatic
activity, nevertheless it is not recognised so strong
a cause-effect relationship to explain all the active
deformation scenarios. it can be supposed that the
instability process is controlled also by other fac-
tors, such as regional tectonics and seismic activity,
that should be further investigated.
