Environmental Engineering Reference
In-Depth Information
7
DeFoRMaBiliTY TesTs
Oedometer Modulus (kPa)
0
2000
4000
6000
8000
10000
12000
0
six oedometer tests were performed, whose results
let highlight the following aspects:
1. compressibility index (cc) ranged between 0.18
and 0.48 with an average value of 0.35. The val-
ues of swelling index (cs) were between 0,011
and 0.031, with an average of 0.019. The ratio
between both coefficients ranged between 15
and 29, with an average of 20.
2. The values of oedometer modulus, without tak-
ing into account the vertical pressure applied,
ranged between 1600 y 15600 kPa, which indi-
cates that the material can be classified as soft
soil with very high deformability. Those values
can be seen in Figure 15.
3. For the interval of vertical stress between 20
and 80 kPa, a clear increase in the value of
oedometer modulus due to the vertical stress is
noted.
4. The most representative value for global oed-
ometer modulus is 2700 kPa; for the interval
between 80 and 300 kPa, the representative
value is 5500 kPa while for the upper step
between 300 and 1000 kPa, the value increases
up to 10500 kPa.
5. Figure 16 shows the variation of those oed-
ometer modulus values with depth taking
into account a natural apparent density of
1.65 t/m
3
and the presence of a phreatic level
in the ground surface. That variation can
be determined by the following expression:
e
oed
(kPa) = 2500 + 75
.
z (m).
6. The consolidation coefficients were between
1 × 10
-2
and 6.8 × 10
-4
cm
2
/s, with a representa-
tive average of 1.5 × 10
-3
cm
2
/s, which indicates
the material has a deficient drainage, so the con-
solidation time can be great.
20
40
E
pres
(kPa) = 35 . z(m) + 8000
60
E
oed
(kPa) = 75.z(m) + 2500
R
2
= 0.9813
80
100
Oedometer tests
Pressuremeter tests
120
Figure 16. Variation of oedometer modulus, deduced
from oedometer and pressuremeter tests, with depth.
The analysis of the deformability values deduced
from the five pressuremeter tests makes it possible
to state the following:
1. The values of pressuremeter modulus are very
low, which indicates tests were performed in a
very deformable material.
2. The ratio between pressuremeter modulus and
limit pressure (ranging between 4.4 and 7.8)
indicates an altered material. Usually, when the
values of that ratio are lower than 5, tests can be
considered as anomalous and bad performed,
due to an excessive ground alteration.
3. The values of oedometer modulus were obtained
multiplying the pressuremeter modulus by a
constant α with a value of 1.5, in accordance
with usual correlations (Briaud, 1992).
4. The values of oedometer modulus, obtained
in such a way, are lightly greater than the ones
deduced from the oedometer tests, as it can be
seen in Figure 16.
5. The variation of oedometer modulus, deduced
from pressuremeter tests, can be quantified by
the following expression:
18000
e
oed, pres.
(kPa) = 8000 + 35 . z (m)
16000
14000
12000
8
oTheR TesTs
10000
one permeability test in triaxial cell and three dis-
persibility test were performed to complete the
characterization of the material. The permeability
coefficient obtained was 1.8 × 10
-7
cm/s, indicative
of a quite impermeable clay material. Permeability
coefficient was also calculated, using one dimen-
sional consolidation theory, based on the values
of the consolidation coefficient (1.5 × 10
-3
cm
2
/s)
and oedometer modulus (5500 kPa). The result
obtained was 2.7 × 10
-6
cm/s.
8000
6000
4000
2000
0
0
200
400
600
800
1000
1200
Vertical Stress (kPa)
Figure 15.
oedometer modulus deduced form oedom-
eter tests.
