ductivity was 1.4 108 cm/s for the test pans pro-
cult as water continued to flow into the test speci-
mens from both the inflow and outflow burettes.
ducing measurable seepage. In April 1994, six test
Therefore, because of the long time required to
pans produced measurable seepage (1, 2, 3, 7, 8,
wait for equilibrium to be established, only one
and 9). The hydraulic conductivity for those
ranged from 1.2 108 to 3.5 108 to 4 107 cm/s.
freezethaw cycle was imposed on the GCL mate-
rials in the laboratory freezethaw tests. None-
Test pans 4, 5, and 6 did not produce any measur-
theless, it was apparent that freezing and thawing
able seepage. The test pan that produced the
reading of 4 107 cm/s (test pan 7) was one of the
did not change the hydraulic conductivity of the
GCL materials and that the hydraulic conductiv-
larger pans with a seam. Excluding the results of
ity of the GCL test specimens was less than 1
that test pan, the average hydraulic conductivity
in April 1994 was 2 108 cm/s. This slight
108 cm/s, both before and after freezing and
thawing for all three of the GCLs. These results
increase in the average hydraulic conductivity
were confirmed by tests conducted by Kraus and
may have been the result of freezethaw, it may
Benson (1994) on field frozen GCLs. As for the
be attributed to improvements in the method
sandbentonite test specimens, higher confining
used to collect data, or it may be scatter that is
pressures than typically used (about 1 lb/in.2 [6.9
within the level of accuracy of these measure-
kPa]) in laboratory hydraulic conductivity tests
ments, or some other unknown factor.
would reduce the swelling problem. However,
Test pan 7 produced the highest seepage of the
the laboratory tests reported here intentionally
nine test pans from the beginning of the test pro-
used low confining pressures commensurate
gram. It contained a large specimen of Claymax
with those in the field tests.
with a seam. The hydraulic conductivity mea-
sured in test pan 7 in December 1993 was always
Field test pan results
the highest of the six, with a maximum measured
value of 3.2 108 cm/s. In April 1994 the mea-
As in the laboratory tests, the hydraulic con-
ductivities (Table 3) of the GCLs in the field test
pans also did not appear to significantly change
This high value could have been caused by a
after freezing and thawing. There are two excep-
number of factors, including construction flaws
tions. At the end of December 1993, the hydraulic
(such as a poor seam), effects of freezethaw, or
conductivity in the nine test pans ranged from no
some other unknown cause. A clear cause of the
measurable seepage from test pans 2, 4, 5, and 6,
increased seepage could not be identified during
to a range of 9 109 to 4 108 cm/s from the
examination of the test pan after it was disassem-
remaining test pans. The average hydraulic con-
bled.
Test pan 2 produced the largest change in mea-
sured hydraulic conductivity before and after
Table 3. Summary of the hydraulic conductivity
freezing. Test pan 2 contained Bentomat with no
tests results in the GCL test pans. All tests were
seam. It generated no measurable seepage before
confined by approximately 0.25 m of pea gravel. Pea
freezing in December 1993. However, in the
gravel was submerged; driving head equals 0.25 m.
spring of 1994, enough seepage was collected to
indicate a hydraulic conductivity below 2 108
Hydraulic
Hydraulic
cm/s. It appears that into late December, after
conductivity
conductivity
Surface
before freeze,
after freeze,
almost 2 months of soaking, the GCL material in
Pan
area
December 1993
April 1994
test pan 2 was not fully hydrated, possibly as a
(m2)
no.
Specimen
(cm/s)
(cm/s)
result of the low surcharge. If the bentonite was
1.5 108
1.9 108
continuing to hydrate during the hydraulic con-
1
Bentomat*
1.8
1.0 108
NMSC†
2
Bentomat
0.64
ductivity measurements in December, then out-
1.0 108
1.4 108
3
Bentomat*
0.65
flow may have been limited to an immeasurable
4
Gundseal*
1.88
NMSC
NMSC
amount. After a season of freezethaw, the bento-
5
Gundseal*
0.65
NMSC
NMSC
nite was likely fully hydrated, therefore allowing
6
Gundseal
0.65
NMSC
NMSC
2.8 108
7 108
7
Claymax*
1.88
seepage.
2.4 108
2.8 108
8
Claymax
0.67
In general the hydraulic conductivities mea-
2.0 108
3.0 108
9
Claymax*
0.69
sured in the field test pans were higher than those
* Specimen included seam, full length of long axis. Dimen-
typically reported in the literature for GCLs un-
sions for test pans 1, 4, and 7 were approximately 1.4 x 1.4
dergoing laboratory tests. The root cause of this is
m. All other test pans were 0.6 x 1.2 m.
unknown. However, we noted some differences
† No measurable seepage collected.
14
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