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Figure 5.4.
SEM Photo of GoG marine sediment at initial state
5.3. Perfect plasticity state and critical void ratio
The comparison of the oedometer model with the triaxial test, in particular the
isotropic triaxial test, presumes that we know the effective stress ratios σ'
h
/σ'
v
. This
ratio
K
0
is considered to be constant by several authors. The following formula by
Jacky is generally used, where Φ
pp
is the friction angle at perfect plastic state:
K
0
= 1 - sin Φ
pp
[5.8]
Thus, the oedometric loading can be represented in the (
e
- log
p
') plane, using
the transformation that depends on Φ
pp
:
p
' = σ'
v
(1+2
K
0
)/3.
The observation confirms the parallelism of the isotropic and oedometric paths,
but does not permit the distance between these two paths to be estimated.
Finally, each path at
q/p'
= η = constant, also has
K
= σ'
3
/σ'
1
= constant, and
appears to be parallel with both lines (oedometric and isotropic) in the (
e
- log
p
')
plane:
- isotropic compression
NC
→η= 0;
- oedometric loading → η=3(1
K
)/(1+2
K
).
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