Geoscience Reference
In-Depth Information
5.2. Biarez's model for the oedometer test
Grains become bonded or “glued”, according to Biarez, due to cementation
during the sedimentation and consolidation processes. If this is the case, the clay is
defined as “non-remolded” or “intact” and the links between the grains, which can
have various origins, form a supplementary parameter for phenomenological
behavior [BIA 98], particularly during oedometric loading.
Where the bond between the grains is missing, as in industrial and post-Glacial
clays, or when the bond has been destroyed, for example by a high loading, the soil
is described as remolded.
It is fundamentally important to study the behavior of material that has been
remolded and reconstituted in the laboratory in normally consolidated and
overconsolidated conditions [BIA 94] because the “intrinsic” mechanical properties
can then be deduced, making it possible to define a fixed reference framework in
order to explain the behavior of natural, non-remolded soils.
Biarez [BIA 72, BIA 75, BIA 77], and more recently Burland [BUR 90],
introduced the concept of intrinsic compression properties in order to describe, in a
normalized plane, the behavior of one-dimensional normally consolidated clay
having been remolded and reconsolidated (at
w
sat
=
1.5
w
L
).
Favre [FAV 72, FAV 80] shows that the Atterberg limits (“nature of grain”
parameters) are particularly helpful in explaining the mechanical properties. In
mineral clays, these properties are strongly linked by the following relation:
I
p
= 0.73(
w
L
- 13)
[5.1]
Thus, the model proposed in Figure 5.2a, plotted with the Casagrande
A
line,
defines the mineralogical nature of the clay.
Moreover, a large number of results collected by Favre [FAV 72, FAV 80] show
that loadings of 6.5 kPa and 1,000 kPa on the oedometric path correspond
statistically on average to
w
L
and
w
P
, respectively (or
e
L
and
e
P
considering
2.7
γγ= , see relation [5.2] and Figure 5.2b). This leads first to equation [5.3] or
[5.4] for the compressibility index C
c
, then to relation [5.5] when using [5.1]
in [5.3].
w
w
sat
=
w
L
for σ'
v
= 6.5 kPa
w
sat
=
w
P
for σ'
v
= 1 MPa
[5.2]
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