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The isotropic loading with
p'
0
= 3 MPa did not provoke grain crushing. The
beginning of the triaxial test is under the theoretical NC (ISL) curve, which classes
the material in the theoretical overconsolidation category (for sands). Its theoretical
overconsolidation stress, following the
C
s
model, is
p'
iC
= 3.5 MPa. Figure 5.13d
represents the results of the simulation by the modified Cam-Clay model of a NC
test on this material.
Both of these paths, one real (
p'
0
= 3 MPa) and the other fictitious
(
p'
0
= 3.5 MPa), are two horizontal straight lines in the (e -
p'
) plane, separated by a
slight gap until the critical void ratio curve. Thus, at the perfect plasticity state,
q
final
for
p'
0
= 3 MPa is a bit smaller than
q
final
would be for
p'
0
= 3.5 MPa. The value
q
final
obtained with this Lee and Seed test shows this small gap; furthermore, the curve,
after the peak (see Figure 5.13d) descends towards
M
before moving up towards this
q
final
final value.
The same phenomenon re-appears for both the other tests at high stresses
(
p'
= 2 MPa and
p'
0
= 1.1 MPa).
0.60
q/p'ic
η = 0.96
M = 1,35
0.55
Lee and Seed tests
Essais de Lee et Seed
essais de SEED
0.50
p'ic = 3,5
p'0 = 3
0.45
0.40
m = 0.88
0.35
0.30
p'ic = 2,9
p'0 = 2
0.25
p'ic = 2,5
p'0 = 1,1
0.20
0.15
0.10
p'ic = 2
p'0 = 0,3
0.05
p'/p'ic
0.00
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
Figure 5.14.
Undrained tests of Lee and Seed [LEE 67]
normalized with their theoretical OCR
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