Environmental Engineering Reference
In-Depth Information
Figure 2. Frequency distribution of cohesion (c) and
friction angle (φ).
Figure 1. structural sketch map and cross section of
etna volcano. VdB-Valle del Bove, RF-Ragalna Fault,
MF-Mascalucia Fault, TF-Trecastagni fault, TFs-Timpe
Fault system, PF-Pernicana Fault, RnF-Ripe della
naca Faults. inset: location of Mt. etna. (1) rock-mass
characterization site; (2) section trace; (3) main structural
elements. Ve-volcanics, a-Mc-apennine-Maghrebian
chain, hP-hyblean Plateau, sec-subetnean clays,
Dc-dyke complex.
Figure 3. a. analysed sliding surface and wedge sub-
division. B. Factor of safety Probability Distribution
Function (saturated case).
modelling, performed by means of finite difference
(FDM) and finite element (FeM) codes.
To support a reliable input dataset for the analysis,
a dedicated structural-mechanical field survey was
carried out along the eastern and southeastern vol-
cano flank, aimed at: i) verifying the main structural
framework controlling the flank instability, ii) char-
acterizing the rock mass geomechanical quality at
outcrop conditions, mainly in lava and flysh units,
and iii) extrapolating average values representative
for deep conditions. some direct geotechnical tests
were carried out at sample scale, to contribute to the
parameterization (koor et al. , 2010).
which are the most affecting and most doubtful
values, a probabilistic analysis was performed
assuming a gaussian frequency distribution of
cohesion (c) and friction angle (φ) and applying
a Monte carlo sampling procedure to each of the
analysed surfaces. The stability analysis consid-
ered two cases: i) a dry slope; ii) a hypothetical
water table in the volcanic edifice and connecting
to the sea level.
The analyses carried out to evaluate possible
rotational sliding phenomena along surfaces several
hundred metres deep show Fos>>1, even taking
into account poorer geotechnical properties and the
effect of a hypothetical deep aquifer ( Fig. 3 ) . con-
sidering sliding surfaces crossing the subetnean clays
unit (cl), and assuming for them a frequency dis-
tribution of cohesion (c) and friction angle (φ), the
instability is never reached (Fos>>1) if gravity is the
only perturbation, in both dry and saturated cases.
2
liMiT eQUiliBRiUM analYsis
a preliminary limit equilibrium analysis (leM)
was carried out in order to determine the Fac-
tor of safety (Fos) related with rotational sliding
occurring in the eastern flank of the volcano. The
involved units are represented by the volcanic edi-
fice (Ve) built-up on the apennine-Maghrebian
flysh (Flcl). The Mohr-coulomb properties are
reported in Table 1.
To take into account the uncertainties in the
shear strength parameters of the Flcl unit,
3
nUMeRical MoDellinG
The numerical modelling was aimed at the recon-
struction of the stress pattern and at a stress-strain
analysis in order to evidence plasticization areas in
conditions of increasing complexity of the model.
 
 
 
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