Geoscience Reference
In-Depth Information
5
σ
1
___
σ
Generalised overconsolidation
3
4
Dilatancy
e
pp
- e
OC
β → Ψ
3
p'
OCR
=
ic
2
e
NC
-e
OC
= (Cc-Cs) log(p'
ic
/p'
i
)
p'
1
(%)
i
1
1 0
2 0
3
e
c
e
1
e
NC
State parameter (e
sp
-e
OC
)≈(e
NC
-e
oc
)-0.1
Isotropic path
0,1
e
NC
-e
OC
0.9
(
η
=0) Cc or
λ
e
pp
Perfect plasticity
e
NC
-e
sp
∼
0.1
0.8
(
η
=M) « critical » e
e
OC
-e
pp
β
dilatancy
0.7
e
OC
Φ
pic
∼∼Φ
pp
+0.6
Ψ
Cs
0.6
ε
1
(%)
p'
0.5
The generalized overconsolidation
can be characterized by several
equivalent parameters for instance: β
or Ψ or (Cc-Cs) or the state
parameter…
1 0
2 0
3 0
0.1
1
10
100
p'
i
0
p'
ic
Fayad-S-biar-Lisb-5167
Figure 5.9.
(e
NC
-e
OC
) and (e
sp
-e
OC
) parameters of the generalized
overconsolidated behavior
There is no well-established model for clean sands. Biarez and Hicher [BIA 94]
propose
C
c
= 0.20 for d
60
/d
10
< 2. This the one we have adopted.
The model for
C
s
is not well established for clays and even less so for sands.
Nevertheless, in accordance with some experimental data [FAV 80, SAI 97], we
have adopted the following models:
C
c
= 0.009(
w
L
- 13)
C
c
/C
s
= 4 for clays
C
c
= 0.20
C
c
/C
s
= 10 for clean sands
For clean sands, Saim [SAI 97] researched the correlations between (
e
NC
- e
OC
)
and (
e
sp
- e
OC
) and the usual parameters of the dilatancy, Ψ and β
max
, and also with
new measurable parameters, such as (
e
OC
- e
pp
) or Φ
peak
:
[ β
max
= (
d
ε
v
/d
ε
1
)
max
and sin ψ =
tg
β
max
/(2+
tg
β
max
) ]
Figure 5.10a gives the (
I
D
- log
p'
) plane graduated with parallel straight lines
having the same Φ
peak
values, Ψ, and
e
NC
- e
OC
. Favre [MEK 02] graduated it with
OCR. In Figure 5.10b,
I
C
- log
p'
gives the graduation with OCR for the clays
around wL = 70%. The gap between ISL and CSL is 0.25 on
I
d
and 0.09 on
I
C
for
these clays.
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