Environmental Engineering Reference
In-Depth Information
volume-mass changes in the soil through use of the soil
constitutive equations. In this way, changes in water con-
tent, void ratio, and degree of saturation of the soil can be
computed at any time during the consolidation process.
from the soil while the flow of air was restricted. Therefore,
the pore-air and pore-water pressures could be independently
controlled. A low-air-entry disk (i.e., coarse porous disk)
was placed on the top of the specimen for the control of
the pore-air pressure. Two rubber membranes separated by
a slotted tin foil were placed around the specimen in order
to reduce air diffusion.
Pore-air and pore-water pressures were translated into the
positive range to prevent cavitation of the water below the
high-air-entry disk (i.e., the axis translation technique). The
total stress, pore-air pressure, and pore-water pressure con-
ditions were controlled throughout the time-dependent mea-
surement of total volume change and water volume change
from the unsaturated soil specimens.
16.4 TYPICAL CONSOLIDATION TEST RESULTS
ON UNSATURATED SOILS
Typical experimental results from consolidation tests on
unsaturated soils are presented to illustrate the consolidation
behavior of an unsaturated soil. The tests require the inde-
pendent measurement or control of pore-air and pore-water
pressures on the boundaries of the soil specimens during
consolidation. The equipment, soil, and test procedures are
described. The results are also best fit with the theory for
unsaturated soil consolidation and swelling.
16.4.2 Presentation of Consolidation Test Results
Five specimens of kaolin were compacted in accordance
with the standard Proctor procedure. The initial volume-mass
properties for each specimen are summarized in Table 16.1.
Each experiment was performed by changing one of
the stress state variable components (i.e., total stress
σ
,
pore-water pressure
u
w
, or pore-air pressure
u
a
). The stress
state component changed in each experiment is summarized
in Table 16.2. The volume change of the overall sample and
the water phase was monitored in each case. However, the
pore-air and pore-water pressure changes within each soil
specimen were not monitored.
16.4.1 Consolidation Tests on Compacted Kaolin
Laboratory experiments were performed on several com-
pacted kaolin specimens using a modified oedometer and
a modified triaxial cell (Fredlund, 1973a). The modified
oedometer was used to perform one-dimensional consoli-
dation tests. The modified triaxial cell was used to perform
isotropic volume change tests.
A high-air-entry disk was sealed into the lower pedestal.
The ceramic disk allowed for the movement of water to and
Table 16.1
Initial Volume-Mass Properties for Specimens Tested
Diameter
Height
Total
Water
Void
Dry Unit
Degree of
Tes t No.
a
Volume (cm
3
)
Ratio,
e
Weight,
γ
d
(kN/
m
3
)
(cm)
(cm)
Content,
w
(%)
Saturation (%)
1
10.006
11.815
929.09
34.32
1.0696
13.185
78.87
2
9.945
11.703
909.10
33.17
1.0251
13.298
80.61
3
10.543
5.867
503.53
29.62
1.2242
11.529
63.29
4
9.832
5.758
437.16
32.12
0.9310
13.281
90.25
5
6.350
2.283
72.29
31.18
1.1247
12.069
72.51
a
All tests performed in a modified triaxial apparatus except test 5, which was performed in a modified oedometer.
Table 16.2 Change in Stress State Variable Components Associated with Each Test
Total Stress,
σ
(kPa)
Pore-Water Pressure,
u
w
(kPa)
Pore-Air Pressure,
u
a
(kPa)
Tes t No.
a
Initial
Final
Initial
Final
Initial
Final
Change (kPa)
1
358.7
560.9
163.8
164.4
214.4
215.6
σ
=+
202
.
2
2
560.9
559.0
164.4
163.1
215.6
421.1
u
w
=+
205
.
5
3
475.1
476.8
41.9
42.2
397.8
206.5
u
a
=−
191
.
3
4
611.4
610.1
177.3
379.2
532.0
530.9
u
w
=+
201
.
9
5
606.7
605.2
216.5
323.6
413.8
413.8
u
w
=+
107
.
1
a
All tests performed in a modified triaxial apparatus except test 5, which was performed in a modified oedometer.
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