Project Summary

United States

Environmental Protection

Agency

Effect of Freeze-Thaw on the

Hydraulic Conductivity of Barrier

Materials: Laboratory and Field

Evaluation

Jason F. Kraus and Craig H. Benson

National Risk Management

Research Laboratory

Cincinnati, OH 45268

Research and Development

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 paper mill sludges.

Analysis of the data showed that

compacted clays undergo large increases in hydraulic conductivity in the

field and laboratory when exposed to

freeze-thaw, with the increase in hydraulic conductivity being larger in the

field. In contrast, both the laboratory

and field tests showed that sand-bentonite 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 increased only if it was not permeated

between freeze-thaw cycles.

This Project Summary was developed

by the EPA's National Risk Management Research Laboratory, Cincinnati,

OH, to announce key findings of the

research project that is fully documented in a separate report of the same

title (see Project Report ordering information at back).

Introduction and Objectives

Laboratory studies conducted by several investigators have shown that freezing and thawing causes compacted clays

to crack. Consequently, their hydraulic conductivity increases dramatically. These

findings suggest that compacted clay barriers 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 generated from laboratory testing, it cannot

be confirmed whether similar increases in

hydraulic conductivity do in fact occur in

the field. In addition, it is not known

whether alternative barrier materials increase in hydraulic conductivity after freezing and thawing. Thus, the objectives of

this study were (1) to determine if the

results of laboratory tests are representative of field conditions and (2) to determine 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 conductivity of two compacted clays and three

alternative barrier materials: a sand-bentonite mixture, three geosynthetic clay liners (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 Deployed in Cold Environments) project conducted 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 conEPA/600/SR-95/118 August 1995
2

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 after 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 Milwaukee, WI area. The hydraulic conductivity

tests were conducted on large undisturbed

block specimens (diameter = 0.3 m) removed from the test pad. Before freezing,

the test pad had low hydraulic conductivity at all depths tested. After freeze-thaw,

however, the hydraulic conductivity increased as much as four orders of magnitude in soil located above the maximum

depth of frost penetration. Below the maximum depth of frost penetration, the hydraulic conductivity was unaltered.

Results of the laboratory freeze-thaw

tests on Parkview clay show that an increase in hydraulic conductivity of approximately 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 increase in hydraulic conductivity occurring

in the field. Comparison of the structure of

the laboratory specimens to the structure

existing in the field showed that cracks in

the laboratory were more closely spaced

and had a smaller aperature.

These findings demonstrate that the hydraulic conductivity of compacted clays

increases as a result of exposure to freezethaw regardless of whether freezing and

thawing occurs in the laboratory or field.

Cracks that form due to desiccation (induced 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 that are observed in freeze-thaw tests conducted in

the laboratory. Larger cracks and a moreblocky structure occur in the field. The

exact cause of this difference in structure

is not known. It possibly can be attributed

to differences in soil structure prior to freezing.

Testing was also conducted to show

that frost damage can be difficult to detect

if the assessment is based on hydraulic

tests performed on specimens collected

in thin-wall sampling tubes. Results 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 collected in

sampling tubes have much lower hydraulic conductivities, which are similar to the

hydraulic conductivities measured on the

specimens removed as blocks prior to

freeze-thaw (Figure 1). Examination of the

specimens collected in sampling tubes

showed that they did not contain the cracks

observed in the field and in the block

specimens. Apparently, the sampling tubes

were too small to capture the cracks existing in the field or caused sufficient disturbance to remold the soil and eliminate

the cracks. These findings suggest that

frost damage should not be assessed by

testing specimens collected in sampling

tubes.

Bentonitic Barriers

Results of the laboratory and field tests

on the bentonitic barrier materials (sandbentonite mixture, GCLs) showed that

these materials are insensitive to freezethaw (e.g., see Tables 2 and 3 for tests

on GCLs, Figure 3 for tests on sandbentonite). The laboratory tests were conducted on disks of GCLs (diameter = 0.15

m) that were permeated in flexible-wall

permeameters. The field tests were conducted using large test pans that con10-10

10-9

10-8

10-7

0123456

Specimen 1

Specimen 2

Hydraulic Conductivity (m/s)

Specimen 3

Number of Freeze-Thaw Cycles

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Before Freezing

After Freezing

10-10 10-9 10-8 10-7 10-6 10-5

Depth (m)

Hydraulic Conductivity (m/s)

Maximum Frost Depth

Parkview Clay

Figure 1. Hydraulic conductivities before and after freeze-thaw

Figure 2. Hydraulic conductivity of specimens of Parkview clay frozen and thawed in the laboratory.
3

Initial Final

Hydraulic Hydraulic

Type of Sample Depth Conductivity Conductivity(1)

Specimen(1) (m) (m/s) (m/s)

Block 0-0.3 1.9 x 10-10 1.9 x 10-6 10,000

Block 0.3-0.6 2.2 x 10-10 4.4 x 10-7 2,000

Block 0.6-0.9 4.5 x 10-10 2.5 x 10-10 0.56

Tube 0.10 2.9 x 10-10 (3) 1.0 x 10-9 0.35

Tube 0.15 2.9 x 10-10 (3) 1.0 x 10-9 0.35

Tube 0.25 2.9 x 10-10 (3) 4.5 x 10-10 1.6

Tube 0.45 2.9 x 10-10 (3) 1.6 x 10-10 0.55

Tube 0.52 2.9 x 10-10 (3) 1.6 x 10-10 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 (Kf/Ki) 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 1. Summary of Hydraulic Conductivity Tests on Specimens from Parkview Test Pad 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-bentonite and thus the structure of the sandbentonite is unchanged by freezing and

thawing. Consequently, the hydraulic conductivity 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 occurs. 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 similarly to the clays. They exhibited compaction curves having a distinct optimum water

content and maximum dry unit weight.

Their hydraulic conductivity was also sensitive to water content, with hydraulic conductivities 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 conductivity increased one to two orders of magnitude. In contrast, the other sludge was

resistant to freeze-thaw if it was permeated after each thaw. However, if this

sludge was frozen and thawed without

intermittent permeation, the hydraulic conductivity increased approximately one

order 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 reTable 2. Summary of Field Hydraulic Conductivity Tests for the GCLs used in the COLDICE project

(courtesy Allan Erickson, CH2M Hill, Inc.)

Before-Winter After-Winter

Hydraulic Hydraulic (1)

Conductivity Conductivity

Specimen Seam? (m/s) (m/s)

Bentomat®, 1.8 m2 Yes 1.5 x 10-10 1.9 x 10-10 1.3

Bentomat®, 0.7 m2 Yes 1.0 x 10-10 1.4 x 10-10 1.4

Bentomat®, 0.7 m2 No no outflow 1.0 x 10-10 N/A(2)

Claymax®, 1.8 m2 Yes 2.8 x 10-10 7.0 x 10-10 25.0

Claymax®, 0.7 m2 Yes 2.0 x 10-10 3.0 x 10-10 1.5

Claymax®, 0.7 m2 No 2.4 x 10-10 2.8 x 10-10 1.2

Note:

1. KA/KB is defined as the ratio of after-winter hydraulic conductivity to before-winter hydraulic

conductivity.

2. N/A = Not Applicable

Table 3. Hydraulic Conductivity of GCLs Frozen and Thawed in the Laboratory

Initial Hydraulic Conductivity After n Freeze-Thaw Cycles, Kn Hydraulic (m/s)

 Conductivity,

K0

Sample Number (m/s) K1 K3 K5 K20

Bentofix®-1 2.9 x 10-11 3.0 x 10-11 2.8 x 10-11 not performed 3.2 x 10-11 1.10

Bentofix®-2 4.9 x 10-11 1.6 x 10-11 2.3 x 10-11 2.7 x 10-11 2.2 x 10-11 0.45

Bentofix®-3 5.6 x 10-11 1.7 x 10-11 3.5 x 10-11 3.6 x 10-11 2.5 x 10-11 0.45

Bentomat®-1 3.1 x 10-11 2.9 x 10-11 2.8 x 10-11 1.3 x 10-11 1.7 x 10-11 0.55

Bentomat®-2 3.1 x 10-11 1.7 x 10-11 2.4 x 10-11 2.5 x 10-11 1.9 x 10-11 0.61

Bentomat®-3 2.9 x 10-11 1.8 x 10-11 1.4 x 10-11 1.5 x 10-11 1.9 x 10-11 0.66

Claymax®-1 3.8 x 10-11 2.9 x 10-11 4.8 x 10-11 4.2 x 10-11 3.4 x 10-11 0.89

Claymax®-2 2.9 x 10-11 2.4 x 10-11 2.7 x 10-11 3.6 x 10-11 2.1 x 10-11 0.72

Claymax®-3 4.2 x 10-11 3.5 x 10-11 3.4 x 10-11 3.2 x 10-11 2.4 x 10-11 0.57

Claymax®-4 4.9 x 10-11 4.1 x 10-11 3.2 x 10-11 4.4 x 10-11 3.3 x 10-11 0.67

K 20

K 0

K f

K i

(2)

K A

K B
4

Jason F. Kraus* and Craig H. Benson are with the University of Wisconsin,

Madison, WI 57306.

 *(currently with CH2M Hill, Inc., Chicago, IL)

Bob Landreth is the EPA Project Officer (see below).

The complete report, entitled "Effect of Freeze-Thaw on the Hydraulic Conductivity of Barrier Materials: Laboratory and Field Evaluation," (Order No.

PB95-253928; 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 permeated in flexible-wall permeameters, increases in hydraulic conductivity of

approximately one order of magnitude

were observed. This discrepancy in hydraulic 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 recommended to address this issue.

The full report was submitted in fulfillment of Cooperative Agreement No. CR

821024-01-0, under the sponsorship of

the U.S. Environmental Protection Agency.

BULK RATE

POSTAGE & FEES PAID

EPA

PERMIT No. G-35

United States

Environmental Protection Agency

National Risk Management Research Laboratory (G-72)

Cincinnati, OH 45268

Official Business

Penalty for Private Use

$300

EPA/600/SR-95/118

Figure 3. Hydraulic conductivity of sand-bentonite frozen and thawed in the laboratory.

10-12

10-11

10-10

10-9

0 1 2 3 4 5 6

Specimen 1

Specimen 2

Specimen 3

Hydraulic Conductivity (m/s)

Number of Freeze-Thaw Cycles