246
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
4
Meanwhile, for the vertical drainage, only minor scattering
values of horizontal displacement increment less than 0.006
mm were observed, as shown in Figure 8. Furthermore, most
of horizontal displacements were less than 0.002 mm, which
is the maximum error in a 90% confidence level, and thus, it
is estimated that horizontal displacements were hardly
detectable under vertical drainage. Vertical displacement
increment during consolidation also showed fairly uniform
distribution along horizontal plane. Uniform vertical
deformation and negligible horizontal deformation is
maintained through the whole consolidation period.
Figure 8. Horizontal displacement increment during consolidation
under vertical drainage condition (
)
0 ~ 5%
ave
U
3.2. Total vertical stress
During the consolidation, the total vertical stresses were
measured from 3 earth pressure gauges at different horizontal
locations on the top of the specimen as shown in Figure 1.
The variation of total vertical stress (measured total vertical
stress minus initial total vertical stress,
v
) with
consolidation time is shown in Figure 9. In the case of vertical
drainage, the vertical total stress maintains constant with
minor scattering. On the other hand, in the case of horizontal
drainage, total vertical stresses changed with consolidation
time in a different manner for each location. At near drainage
location, total vertical stress initially decreased and then
increased at 35% of
ave
U
. At the end of consolidation, it
reached net increase of total stress. Meanwhile, at mid-plane
and far drainage locations, total stresses initially increase and
then decrease. At the end, net decreases of total stresses were
observed.
Figure 9. Variation of total vertical stress during consolidation
These total stress variations are strongly related to
progressive consolidation process from drained boundary. As
mentioned above, initial decrease of void ratio at near
drainage induces increase of total stress nearby zone such as
mid-plane location. And as consolidation progresses, void
ratio of entire horizontal plane decreases and ideally reaches
to the same void ratio value at completion of consolidation. In
this case, even distribution of total vertical stress is expected.
However, uneven void ratio distribution at the end (i.e.,
decreasing value of void ratio as approaching drained
boundary) yields higher total vertical stress at near drainage
and lower at far drainage.
4
.
CONCLUSIONS
In this study, consolidation tests were performed under the
condition of horizontal and vertical drainage using the newly
developed consolidation apparatus. The developed equipment
can monitor inner soil deformations visually and measure the
pore water pressure distributions inside the specimen.
Results of digital image analysis and vertical total stress
measurement during the experiment are briefly presented as
follows. Horizontal displacements for horizontal drainage
under vertical loading were predominantly observed. In the
early stage of consolidation, significant horizontal
displacements to the drainage were observed, and thereafter it
is decreasing as consolidation proceeds, and at the last stage
of 70 % or more of U
ave
, relatively small amount of horizontal
displacements in opposite direction were monitored. On the
other hand, only minor scattering values of horizontal
displacement were measured for vertical drainage condition.
The induced non-uniformity was confirmed by measuring
water content at the end of the consolidation: as approaching
to the drainage surface, the measured water contents were
decreasing.
The total vertical stress in the horizontal plane measured
by three earth pressure gauges showed constant values in
vertical drainage conditions. In the horizontal drainage, total
vertical stress near drainage boundary initially decreased and
then increased, reaching net increase (12 %)
.
Meanwhile, at
mid-plane and far drainage locations, total stresses initially
increased and then decreased, finally having net decrease. (7,
30% respectively)
5
.
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