United States
Environmental Protection
Agency
National Risk Management
Research Laboratory
Cincinnati, OH 45268
Research and Development
EPA/600/SR-95/118 August 1995
&EPA Project Summary
Effect of Freeze-Thaw on the
Hydraulic Conductivity of Barrier
Materials: Laboratory and Field
Evaluation
Jason F. Kraus and Craig H. Benson
Laboratory tests were conducted on
barrier materials to determine if their
hydraulic conductivity changes as a
result of freezing and thawing. Results
of the tests were compared to data
collected from a field study. Tests were
conducted on two compacted clays,
one sand-bentonite mixture, three
geosynthetic clay liners, and three pa-
per mill sludges.
Analysis of the data showed that
compacted clays undergo large in-
creases in hydraulic conductivity in the
field and laboratory when exposed to
freeze-thaw, with the increase in hy-
draulic conductivity being larger in the
field. In contrast, both the laboratory
and field tests showed that sand-ben-
tonite mixtures and geosynthetic clay
liners are not affected by freeze-thaw.
The sludges behaved similar to the
clays, that is, they show large increases
in hydraulic conductivity when frozen
and thawed. However, the hydraulic
conductivity of one of the sludges in-
creased only if it was not permeated
between freeze-thaw cycles.
This Project Summary was developed
by the EPA's National Risk Manage-
ment Research Laboratory, Cincinnati,
OH, to announce key findings of the
research project that is fully docu-
mented in a separate report of the same
title (see Project Report ordering infor-
mation at back).
Introduction and Objectives
Laboratory studies conducted by sev-
eral investigators have shown that freez-
ing and thawing causes compacted clays
to crack. Consequently, their hydraulic con-
ductivity increases dramatically. These
findings suggest that compacted clay bar-
riers used in liners and covers for waste
containment facilities may be damaged if
not protected from frost. However, because
the data collected to date have been gen-
erated from laboratory testing, it cannot
be confirmed whether similar increases in
hycraulic conductivity do in fact occur in
the field. In addition, it is not known
whether alternative barrier materials in-
crease in hydraulic conductivity after freez-
ing and thawing. Thus, the objectives of
this study were (1) to determine if the
results of laboratory tests are representa-
tive of field conditions and (2) to deter-
mine if alternative barrier materials are
deleteriously affected by frost.
To meet these objectives, tests were
performed in the laboratory to assess how
freeze-thaw affected the hydraulic con-
ductivity of two compacted clays and three
alternative barrier materials: a sand-ben-
tonite mixture, three geosynthetic clay lin-
ers (GCLs), and three paper mill sludges.
Results of laboratory tests on the clays,
sand-bentonite mixture, and GCLs were
compared to data obtained from the
COLDICE (Construction of Liners De-
ployed in Cold Environments) project con-
ducted by the U. S. Army Cold Regions
Research and Engineering Laboratory
(CRREL) and CH2M Hill, Inc. The
COLDICE project is a large-scale field
study designed to evaluate the effect of
freeze-thaw on the hydraulic conductivity
of barrier materials. Results of laboratory
tests performed on the paper mill sludges
were compared to results of hydraulic con-
Printedon Recycled Paper
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ductivity tests performed in a small-scale
field study conducted at the University of
Wisconsin-Madison. The small-scale field
study consisted of compacting paper mill
sludge in large PVC pipes and measuring
their hydraulic conductivity before and af-
ter exposure to freeze-thaw.
Compacted Clays
Typical results obtained from the field
study are shown in Figure 1. The graph
shows hydraulic conductivity vs. depth in
a test pad constructed with Parkview clay,
a low plasticity glacial till from the Milwau-
kee, Wl area. The hydraulic conductivity
tests were conducted on large undisturbed
block specimens (diameter = 0.3 m) re-
moved from the test pad. Before freezing,
the test pad had low hydraulic conductiv-
ity at all depths tested. After freeze-thaw,
however, the hydraulic conductivity in-
creased as much as four orders of magni-
tude in soil located above the maximum
depth of frost penetration. Below the maxi-
mum depth of frost penetration, the hy-
draulic conductivity was unaltered.
Results of the laboratory freeze-thaw
tests on Parkview clay show that an in-
crease in hydraulic conductivity of approxi-
mately two orders of magnitude occurred
as a result of freeze-thaw (Figure 2). This
increase in hydraulic conductivity is two
orders of magnitude smaller than the in-
crease in hydraulic conductivity occurring
Hydraulic Conductivity (rh/s)
Parkview Clay
Before Freezing
After Freezing
Maximum Frost Depth
Flguro 1. Hydraulic conductivities before and after freeze-thaw
•5 10'8 ,
•o
o
O
.o
1
I,
Specimen 1
Specimen 2
—-o— Specimen 3
12345
Number of Freeze-Thaw Cycles
Figure Z Hydraulic conductivity of specimens of Parkview clay frozen and thawed in the laboratory.
in the field. Comparison of the stiucture of
the laboratory specimens to the structure
existing in the field showed that tracks in
the laboratory were more closer/ spaced
and had a smaller aperature.
These findings demonstrate that the hy-
draulic conductivity of compactsd clays
increases as a result of exposure o freeze-
thaw regardless of whether freezing and
thawing occurs in the laboratory or field.
Cracks that form due to desiccation (in-
duced by freezing) and formation of ice
lenses are responsible for the increase in
hydraulic conductivity. However, greater
increases in hydraulic conductivity occur
in the field relative to those tha: are ob-
served in freeze-thaw tests conducted in
the laboratory. Larger cracks and a more-
blocky structure occur in the feld. The
—exact-cause oHhis difference- in structure -
is not known. It possibly can be attributed
to differences in soil structure prio to freez-
ing.
Testing was also conducted to show
that frost damage can be difficult to detect
if the assessment is based on nydraulic
tests performed on specimens collected
in thin-wall sampling tubes. Resul s of tests
conducted on specimens collected after
freezing and thawing from the test pad
constructed with Parkview clay are shown
in Table 1. The specimens were collected
as blocks (diameter = 0.3 m) and with
sampling tubes having an inside diameter
of 0.071 m. The specimens co lected in
sampling tubes have much lowe' hydrau-
lic conductivities, which are simi ar to the
hydraulic conductivities measured on the
specimens removed as blocks prior to
freeze-thaw (Figure 1). Examinat on of the
specimens collected in sampling tubes
showed that they did not contain the cracks
observed in the field and in tie block
specimens. Apparently, the sampling tubes
were too small to capture the c acks ex-
isting in the field or caused sufficient dis-
—turbance to remold the~soil and eliminate
the cracks. These findings suggest that
frost damage should not be ac^ossed by
testing specimens collected in sampling
tubes.
Bentonitic Barriers
Results of the laboratory and Held tests
on the bentonitic barrier materials (sand-
bentonite mixture, GCLs) showed that
these materials are insensitive to freeze-
thaw (e.g., see Tables 2 and 3 for tests
on GCLs, Figure 3 for tests on sand-
bentonite). The laboratory tests were con-
ducted on disks of GCLs (diameter = 0.15
m) that were permeated in flexible-wall
permeameters. The field tests were con-
ducted using large test pans that con-
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Table 1. Summary of Hydraulic Conductivity Tests on Specimens from Parkview Test Pad
Type of
Specimen '>
Block
Block
Block
Tube
Tube
Tube
Tube
Tube
Sample Depth
(m)
0-0.3
0.3-0.6
0.6-0.9
0.10
0.15
0.25
0.45
0.52
Initial
Hydraulic
Conductivity
(m/s)
1.9x10-1°
2.2 x 1CT10
4.5X1CT10
2.9x1 Or1 0(3)
2.9 x 10-10 (3)
2.9 x 10r10 (3)
2.9x10-w(3)
2.9x10-'° (3)
Final
Hydraulic
Conductivity(1)
(m/s)
1.9X10T6
4.4 x 10~7
2.5 x 10-1°
1.0x 1(r9
I.OxKT9
4.5x10-1°
1.6x10-1°
1.6 x10-10
Kf<2>
Ki
10,000
2,000
0.56
0.35
0.35
1.6
0.55
0.55
Notes:
1. Hydraulic conductivities are reported as averages for specimens removed from the test pad from
a depth of 0-0.3 m after winter (2 specimens)
2. Change in hydraulic conductivity (K//K/) is defined as the final hydraulic conductivity divided by
the initial hydraulic conductivity.
3. No specimens collected before winter in thin wall tubes; thus average hydraulic conductivity is
reported as the average hydraulic conductivity for the block specimens collected before winter.
Table 2. Summary of Field Hydraulic Conductivity Tests for the GCLs used in the COLDICE project
(courtesy Allan Erickson, CH2M Hill, Inc.)
Specimen
Bentomai®, 1.8m2
Bentomai®, 0.7m2
Bentomai®, 0.7m2
Claymax®, 1.8m2
Claymax®, 0.7 m2
Claymax®, 0.7 m2
Seam?
Yes
Yes
No
Yes
Yes
No
Before-Winter
Hydraulic
Conductivity
(m/s)
1.5x10-1°
1.0x 10-'°
no outflow
2.8 x 10r10
2.0 x 10-1°
2.4 x 10-1°
After-Winter
Hydraulic
Conductivity
(m/s)
1.9x10-10
1.4x10-1°
1.0x10-1°
7.0x10-1°
2.8x10-1°
K±(1)
KB
1.3
1.4
N/A(2)
25.0
1.5
1.2
Note:
1. KP/KQ is defined as the ratio of after-winter hydraulic conductivity to before-winter hydraulic
conductivity.
2. N/A = Not Applicable
tained a double-ring underdrain to collect
effluent from the GCLs
[Examination of both frozen and thawed
specimens of the sand-bentonite showed
that ice lenses do not form in sand-bento-
nite and thus the structure of the sand-
bentonite is unchanged by freezing and
thawing. Consequently, the hydraulic con-
ductivity does not change. In contrast, ice
lenses do form in hydrated GCLs when
they freeze, but the resulting cracks in the
soft bentonite close during thawing. Thus,
no increase in hydraulic conductivity oc-
curs. This behavior is in direct contrast to
the behavior of compacted clays, which
are relatively stiff and retain the cracks
incurred during freezing after thawing has
occurred.
Paper Mill Sludges
The paper mill sludges behaved simi-
larly to the clays. They exhibited compac-
tion curves having a distinct optimum water
content and maximum dry unit weight.
Their hydraulic conductivity was also sen-
sitive to water content, with hydraulic con-
ductivities less than 1 x 10~9 m/s occurring
wet of optimum water content.
Two of the sludges behaved nearly the
same as compacted clay when subjected
to freeze-thaw. Their hydraulic conductiv-
ity increased one to two orders of magni-
tude. In contrast, the other sludge was
resistant to freeze-thaw if it was perme-
ated after each thaw. However, if this
sludge was frozen and thawed without
intermittent permeation, the hydraulic con-
ductivity increased approximately one
orcer of magnitude.
The small-scale field tests with the
sludge were inconclusive. When the field
specimens were permeated in the pipes,
a reduction in hydraulic conductivity was
observed after one winter of freeze-thaw.
However, when the specimens were re-
Table 3. Hydraulic Conductivity of GCLs Frozen and Thawed in the Laboratory
Sample Number
Bentofix®-1
Bentofix®-2
Bentofix®-3
Bentoma^-1
Bentoma^-2
Bentoma@-3
Clay max®- 1
Claymax®-2
Claymax®-3
Claymax®-4
Initial
Hydraulic
Conductivity,
KO
(m/s)
2.9 x 10-1 1
4.9x10-11
5.6x10-11
3.1x10-11
3.1x10-11
2.9x10-11
3.8x10-11
2.9x10-11
4.2x10-11
4.9x10-11
Hydraulic Conductivity After n Freeze-Thaw Cycles, Kn
(m/s)
K1
3.0x10-11
1.6x10-11
1.7x10-11
2.9 x 10-11
1.7x 10-11
1.8x10-11
2.9x10-11
2.4x10-11
3.5x10-11
4.1 x 10-11
K3
2.8x10-11
2.3x10-11
3.5x10-11
2.8 x 10-11
2.4x10-11
1.4x10-11
4.8 x 10-11
2.7 x 10-11
3.4x10-11
3.2x10-11
t<5
not performed
2.7x10-11
3.6x10-11
1.3x10-11
2.5x10-11
1.5x10-11
4.2x10-11
3.6x10-11
3.2x10-11
4.4x10-11
K20
3.2x10-11
' 2.2x10-11
2.5x10r11
1.7x10-11
, 1.9x10-11
1.9x10-11
3.4x10-11
2.1x10-11
2.4x10-11
3.3x10-11
K20
K0
1.10
0.45
0.45
0.55
0.61
0.66
0.89
0.72
0.57
0.67
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Jason F. Kraus* and Craig H. Benson are with the University of Wisconsin,
Madison, Wl 57306.
'(currently with CH2MHHI, Inc., Chicago, IL)
Bob Landreth is the EPA Project Officer (see below).
The complete report, entitled "Effect of Freeze-Thaw on the Hydraulic Conduc-
tivity of Barrier Materials: Laboratory and Field Evaluation," (Order No.
PB9S-253928; Cost: $27.00, subject to change) will be available only
from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
National Risk Management Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
moved from the pipes as slices and per-
meated in flexible-wall permeameters, in-
creases in hydraulic conductivity of
approximately one order of magnitude
were observed. This discrepancy in hy-
draulic conductivity may have been the
result of disturbance incurred when the
specimens were sliced from the pipes.
Nevertheless, the effect that freeze-thaw
has on paper mill sludges in the field is
not clear. Large-scale field tests are rec-
ommended to address this issue.
The full report was submitted in fulfill-
ment of Cooperative Agreement No. CR
821024-01-0, under the sponsorship of
the U.S. Environmental Protection Agency.
I
•i" 10'
10
1 10"' '
• Specimen 1
• Specimen 2
• Specimen 3
0123456
Number of Freeze-Thaw Cycles
Flgura 3. Hydraulic conductivity of sand-bentonite frozen and thawed in the laboratory.
United States
Environmental Protection Agency
National Risk Management Research Laboratory (G-72)
Cincinnati, OH 45268
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