Geoscience Reference
In-Depth Information
of heavy rainfall. The infrastructure of the commune: roads, railway, buildings, etc. was
heavily damaged. A morphological cut of the site was reconstituted for the purposes
of the project and is reproduced in Figure 8.6. In this image, the dashed lines cutting
boreholes depict the zones where the
in situ
slip surface was found; that is, between
70
and
90
meters deep. The grayscale distinguishes the different materials. Aside
the superficial layers, the soil is largely homogeneous, with a grain size distribution
situated between clays and silts. Table 8.1 gives the principal morphological features of
the soil.
Features of particle size
large particles
(φ>
2mm
)
0.0%
sands
(
0.06
<φ<
2mm
)
6.1%
silts
(
0.002
<φ<
0.06 mm
)
55.7%
clays
(φ<
0.002 mm
)
38.2%
General features
grain density
(γ
s
)
2.74 g/cm
3
initial void ratio
(e)
0.517
initial saturation degree
(S
r
)
99.90%
liquid limit
(LL)
58.41%
plasticity limit
(LP )
21.44%
Table 8.1.
General features of the Petacciato soil
8.3.2.
Description of the model used
To perform this modeling, we used the Lagamine code [LAG 07] developed at the
Liège University. This code has at its disposal a non-associated elastoplastic law for
the description of the soil's mechanical behavior [BAR 98]. This model is based on the
Van-Eekelen loading surface [VAN 80a] where the conic shape depends on the current
friction angle
ϕ
and the current cohesion
C
. Figure 8.7 depicts a comparison between
the Mohr-Coulomb, Drücker-Prager and Van-Eekelen surfaces in the deviatoric plane.
Hardening is taken into account by a hyperbolic evolution of the cohesion
C
and the
friction angle
ϕ
with the Von Mises equivalent plastic strain. The initial values of
C
and
ϕ
provide the elastic limit and their maximum values provide the plastic limit:
⎧
⎨
(ϕ
cf
−ϕ
c0
)ε
eq
B
p
+ε
eq
ϕ
c
= ϕ
c0
+
(ϕ
ef
−ϕ
e0
)ε
eq
B
p
+ε
eq
ϕ
e
= ϕ
e0
+
[8.18]
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