1204
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
2 MATERIAL USED IN THE RESEARCH
2.1
Composition and characterization of material
The material used is a mixture of sand (30%), silt (32%) and
clay (38%) (v. Figure 1). The analysis by X-ray diffraction
indicates that the soil mixture consists of quartz, calcite,
dolomite and vermiculite.
Figure 1. Soil mixture
Table 1 summarizes the results obtained from the analysis
of the major chemical compounds present in the samples tested
by the method of quantitative Pyrite.
Table 1. Major compounds present in the sample
S i O
2
Al
2
O
3
F e
2
O
3
MgO CaO
K
2
O
47.9%
6.0%
2.8%
1.5% 9.8%
1.3%
C a l c i n a t i o n
loss
O t h e r s
19.0%
1.72%
Table 2 summarizes the characterization tests of the soil
mixture. The initial suction (
Ψ
0
), was obtained with a
sphygmomanometer T5x-UMS.
Table 2. Characterization tests of soil mixture
T200
(%)
w
opt
(%)
ρ
max
(kg/m
3
)
ρ
s
(kg/m
3
)
e
0
S
r
(%)
73.49
14.5
1795
2700
0.68
45
w
L
I
P
Ψ
0
(kPa)
31
13.6
95.4
To obtain a more open structure that guarantees a collapsing
behavior, the sample was compacted to 90% of the Proctor
standard maximum dry density (1615 kg/m
3
). As the moisture
content (8.8%), corresponding to this density in the Proctor
curve, prevented obtaining acceptable handling conditions (it
crumbled when removed from the compaction ring), it was
finally compacted to a moisture content of 11.3% and
ρ
d
=1615
kg/m
3
.
2.2 Soil water characteristic curve (SWCC)
The techniques used to implement and control the suction in the
different samples may be grouped by ranges as indicated below:
1. Pressure membrane for suctions less than 500 kPa.
2. Vapour equilibrium in vacuum desicator, with saline
solutions (NaCl, CaCl
2
) for suctions ranging from 500
kPa to 150 MPa.
3. Vapour equilibrium in vacuum desicator, with acid
solution (H
2
SO
4
) for suctions exceeding 150 MPa.
The time required to reach equilibrium under the imposed
suction was determined before performing the experimental
tests scheduled. In test specimens in the pressure membrane
apparatus, a suction of 400 kPa was applied for several days.
Every two days the samples were weighed and it was found that
the weight stabilized in eight days.
In the experimental phase stabilization times were greater, at
least ten days for all samples tested, thus ensuring that suction
equilibrium was reached.
Figure 2 shows the SWCC for the drying paths from the
initial suction and the subsequent wetting paths.
Figure 2. Soil water characteristic curve
3 EQUIPMENT
AND
EXPERIMENTAL
METHODOLOGY
3.1
Experimental techniques
Oedometer tests have been performed on cells that control the
suction of the soil mixture
,
using the technique of axis
translation and keeping constant the vertical pressure (see
Figure 3).
All
t
ests have been carried out in a room with controlled
temperature (20±1 ºC) and relative humidity of
65±2%.
Figure 3. Suction controlled oedometric cell.
