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Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
residual shrinkage, air enters the pores close to the shrinkage
limit and pulls the particles together due to suction. This leads
to a further decrease in soil volume albeit lower than the volume
of water lost. Furthermore, the high volume change and the
closeness to the saturation line during normal shrinkage
corresponded well with the comparatively looser state and a
relatively homogeneous structure of the compacted sample.
Finally, the observed shrinkage curve is reversible because the
in situ soil has undergone numerous swell-shrink cycles since
deposition. Likewise, Tripathy et al. (2002) reported that
equilibrium conditions are usually attained after about four
cycles in compacted soils.
4 CONCLUSIONS
S
= 70%
0
10
20
30
40
50
Gravimetric Water Content (%)
0.2
0.6
1.0
1.4
Void Ratio
In situ soil
Compacted soil
S
= 100%
S
= 60%
S
= 50%
S
= 80%
The engineering properties of a typical expansive soil (from
Regina, Saskatchewan, Canada) were investigated under in situ
and compacted conditions. For both sample types, the clay
behavior was characterized by its internal structure comprising
of fissures and aggregates. The SWCC using water content on
the ordinate showed a bimodal distribution with two air entry
values: a lower value (10 kPa) corresponding to drainage
through fissures followed by a higher value (300 kPa for the in
situ sample and 100 kPa for the compacted sample) associated
with seepage through the soil matrix. Sample type became
irrelevant when the flow started to occur through the soil
matrix. The matrix air entry value was found to be about 6000
kPa when the SWCC was plotted in the form of the degree of
saturation versus soil suction. Likewise, the shrinkage curve
was found to be S-shaped and included a low structural
shrinkage followed by a sharp decline during normal shrinkage
and then by a low decrease during residual shrinkage. The
extent of volume change that depends on the initial void ratio
must be calculated from the reversible swell-shrink curve.
5 ACKNOWLEDGEMENTS
The authors acknowledge the material and financial support
provided by the Saskatchewan Ministry of Highways and
Infrastructure and the University of Regina for providing
laboratory space.
Figure 4. Shrinkage curve
Theoretically, the shrinkage curve comprises of two straight
lines: a sloped line closely following the
S
= 100% line that
joins a horizontal line at a void ratio associated with the
shrinkage limit of the soil. This means that soils essentially
remain saturated up to the shrinkage limit following a J-shaped
curve. Due to the presence of fissures, the investigated soil (in
both in situ and compacted conditions) exhibited deviations
from this theoretical behavior.
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