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5.9. A new model to analyze the oedometer's path
This study, partly conducted with Biarez, wished to compare the predictions of
two models for the compression of reconstituted normally consolidated clays under
oedometric loading. The Biarez model presented in section 5.2 uses the liquidity
index I L , and the more recent Burland model introduces I v, a normalized void index
based on two characteristic void ratios ( *
and
e ) , corresponding to the
*
100
1000
oedometric curve of σ' v =100 kPa and σ' v =1,000 kPa.
These models, which represent the intrinsic properties of clays under
compression, are compared via two experimental curves: one representing a
remolded and reconstituted clay (Kaolinite P300) [HAT 04]; and the other, a
deepwater clay sediment (GoG clay) taken from the Gulf of Guinea at a depth of
700 m [FAV 06].
5.9.1. Burland's model
Burland [BUR 90] collected and analyzed the oedometric compressibility of
several clay sediments with a liquid limit w L varying from 25% to 159%, remolded
and reconstituted in the laboratory. The curves obtained in the (
elo − σ plane
are slightly concave when σ' v is located between 10 kPa and 1,000 kPa (see
Figure 5.19a). The intrinsic compressibility index
' v
*
c C is, therefore, introduced [5.26]
as the difference between
an e e , two characteristic quantities corresponding
to the consolidation stresses at 100 kPa and 1,000 kPa, respectively.
*
*
100
1000
*
c C is also the
slope of the oedometric compression curve (linear in this interval of stresses), the
quantity
{
}
[
]
− − b e i n g equal to 1. With the transformation of the
variable defined in [5.27], and by introducing the normalized void index I v , the
Burland model requires all experimental curves to pass through two fixed points in
the (
log(100) log(1,000)
I-log σ plane, corresponding to
ee I
=
*
100 ,
=
0
and
ee I
=
*
1,000 ,
= −
1
for
V
V
σ' v = 100 kPa and σ' v = 1,000 kPa, respectively.
c Ce e
*
=−
*
*
[5.26]
100
1000
ee
*
100
I
=
[5.27]
v
C
*
c
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