United States
Environmental Protection
Agency
Risk Reduction
Engineering Laboratory
Cincinnati OH 45268
Research and Development
EPA/600/S2-88/067 Jan. 1990
<>EPA Project Summary
Field and Laboratory
Testing of a Compacted
Soil Liner
Bill R. Elshury, Gregory A. Sraders, David C. Anderson, James A. Rehage,
Joseph O. Sai, and David E. Daniel
This project was initiated to provide
information on the construction
criteria that control the performance
of compacted soil liners. The infor-
mation generated by this study is
intended to be used in regulating,
designing, and constructing soil
liners to meet the mandated
maximum hydraulic conductivity of 1
x 10-7 cm per sec.
The construction criteria that have
the greatest impact on soil liner
performance were identified. A field
liner was designed and constructed.
After construction, the hydraulic
conductivity of the liner was
measured in the field using four 25-
sq-ft (2.3-sq-m) sealed infiltrometers
set in the liner surface and a 256-sq-ft
(23.8-sq-m) lysimeter set in a gravel
underdrain. Dye was introduced into
one of the infiltrometers and a
borehole, and the adjacent liner was
dissected to expose the features of
the liner that control its hydraulic
conductivity.
An extensive program of laboratory
testing of compacted specimens,
prepared from the same soil as the
liner, was completed. Test specimens
were prepared using impact compac-
tion, kneading compaction, and static
compaction, with two levels of
compactive effort for each time of
compaction. Laboratory tests were
also performed on samples of the
field liner using several techniques.
This Project Summary was devel-
oped by EPA's Riske Reduction Engi-
neering 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
In response to the widespread use of
low-permeability compacted soil liners for
hazardous waste facilities and the
scarcity of performance data on such
liners, the U.S. Environmental Protection
Agency (EPA) initiated this project to
develop a better understanding of the
construction criteria that affect the
hydraulic conductivity of compacted soil
liners.
The principal purposes of this project
were to:
• identify the construction criteria that
control the hydraulic conductivity of
compacted soil liners,
• measure the hydraulic conductivity of a
field liner constructed with full-sized
construction equipment, and
• determine the applicability of labora-
tory tests to in-the-field performance.
The research program began by
identifying the construction criteria that
are most influential in determining the
hydraulic conductivity of compacted soil
liners (Phase I). Based on the findings of
the initial efforts, a program of
construction and field testing of a series
of small, 2-ft-thick (61-cm-thick) test
liners, which were to be constructed
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using a variety of compaction equipment
and various soil moisture contents, was
planned (Phase II). A "trial pad" was buiit
with full-sized construction equipment
using two compaction techniques. The
hydraulic conductivity of that liner was
measured with both field and laboratory
techniques. Laboratory hydraulic con-
ductivity tests were conducted on
samples of soil used to construct the
liner. Dye was introduced into the liner at
two locations, and morphological exam-
inations were made to study the
mechanisms of seepage through the
liner.
After the trail pad was completed, the
scope of the project was reduced and the
trial pad, which was intended to be
mostly for technique verification, became
the only field liner constructed. The trail
nature of the liner led to some choices
during design and construction that would
have been different had the other liners
not been planned.
Field Liner
In general terms, the field liner con-
sisted of two 6-in. lifts of clay compacted
over an underdrain of clean coarse
gravel, with a fabricated wall to impound
1 ft (30 cm) of water. The ponded area
was about 32 ft (9.8 m) by 37 ft (11.3 m)
in plan dimensions.
The liner was constructed of highly
plastic clay (CH), which had an average
liquid limit of 56, an average plasticity
index of 41, 82 percent passing the No.
200 sieve, and 4 percent calcium
carbonate. The clay fraction of the soil
(about 42 percent finer than 2 pm) was
predominantly smectite.
The liner was constructed in two
portions with a padfoot roller that could
be operated either in a static or vibratory
mode. One of the two sections of the
liner was constructed with 8 passes of
the roller in the static mode, and the
other was compacted by 3 to 4 passes of
the roller in the vibratory mode. The roller
had a single drum with 104 pads that
were 3 in. (76 mm) high and had an end
area of 21 sq in. (135 sq cm). The roller
weighed about 15,950 Ib (7240 kg); it
could deliver a vibratory force of 26,500
Ib (118 kN) at a frequency of 30.8 Hz and
an amplitude of 0.040 in. (1.0 mm).
Construction testing of the static sec-
tion (7 tests) gave an average moisture
content of 15.7 percent with a standard
deviation of 0.8 percent and an average
dry density of 110.4 Ib per cu ft (17.34
kN per cu m) with a standard deviation of
2.7 Ib per cu ft (0.42 kN per cu m). All
tests met the planned 95 percent of
maximum standard Proctor dry density.
Maximum standard Proctor dry density
was 108 Ib per cu ft (17.0 kN per cu m) at
17 percent moisture, and maximum
modified Proctor dry density was 123 Ib
per cu ft (19.3 kN per cu m) at 12 percent
moisture.
Construction testing of the vibratory-
compacted section (30 tests) gave an
average moisture content of 16.4 percent
with a standard deviation of 1.3 percent
and an average dry density of 108.9 Ib
per cu ft (17.11 kN per cu m) with a
standard deviation of 6.3 Ib per cu ft (0.99
kN per cu m). Five of the tests failed to
meet the planned 95 percent of
maximum standard Proctor dry density.
The pond was filled with water to a
depth of 1 ft (30 cm) for 22 days, during
which time several sets of measurements
of hydraulic conductivity were taken with
the lysimeter and the infiltrometers. Data
from the observations are given in Figure
1. The average hydraulic conductivity of
the portion of the liner compacted with
the roller in the static mode was 3 x 10-5
cm per sec, and the average for the
portion compacted with vibration was 1 x
10-4cm per sec.
After the pond was drained, methylene
blue dye was introduced into one of the
infiltrometers and a borehole in the liner.
The adjacent liner was later dissected.
The dye penetrated over 80 percent of
the thickness of the liner in thin, isolated
channels that were separated by intact
clods of clay with no dye staining.
Samples of the liner were taken before
pondinq using 3-in.- and 6-in.-diameter
(76-mm- and 152-mm-) thin-walled tube
samplers. Two hand trimmed block
samples were taken after the pond was
drained.
Laboratory Hydraulic
Conductivity Tests
Samples of the soil used for the liner
were compacted using 7 different pro-
cedures as listed in Table 1. The soil for
one series of tests was prepared by air
drying and passing it through a No. 4
sieve. The other samples were molded
with soil that had not been predried and
that had a maximum clod size of 0.75 in.
(19 mm). Four compaction curves for
soils compacted with impact compaction
are given in Figure 2.
The compacted specimens were sub-
jected to laboratory hydraulic conduc-
tivity tests using principally fixed-wall
permeameters. The results of these tests
are presented in Figure 3, which shows
the influence of moisture content on
hydraulic conductivity. The influence of
soil dry density is shown on Figure
The values from the field hydrau
conductivity tests are shown in bo
figures for comparison. Laborato
hydraulic conductivity tests were al
conducted on samples of the liner,
given in Table 2.
Conclusions
The factors that are believed
influence the hydraulic conductivity
compacted soil liners were divided in
five groups: (1) soil type, (2) bas
compaction objectives, (3) essenti
choices that are necessary to meet tl
basic objectives, (4) supporting elemen
that are included in or subsidiary to tl
essential choices, and (5) other co
siderations.
The "basic objectives" that must I
met for a compacted liner to have
hydraulic conductivity of 1 x 10-7 cm p
sec or less are: (1) destruction of si
clods and (2) bonding between lifts.
The "essential choices" to be made
achieve the "basic objectives" are (1) tl
moisture content of the soil, (2) the tyi
and weight of the roller, (3) the thickne
of each lift, (4) the size of clods befo
compaction, and (5) the number
passes by the roller. Soil moisture co
tent is considered the most importa
essential choice. The soil must be w
(and therefore soft) enough for the roll
to thoroughly remold both the new lift ar
any loose soil at the top of the underlyir
lift. The soil for the field liner constructs
in this study was too dry (and thereto
too strong) for the relatively light roll
used to construct the liner.
The "supporting elements" of densi
and degree of saturation are important
achieving low hydraulic conductivity ar
are useful indicators in controllir
compaction in the field. But, if the "bas
objectives" are not met, both factors ha>
little meaning.
Examinations of the dye-stained ffc
paths in the field liner clearly showed th
the seepage was predominantly throuc
macrovoids between soil clods and alor
the interlift boundary, not through tt
finer pores between the soil particles
the clods. The observations do n
support the flocculated/dispersed mec
anism that is frequently used to expla
flow through compacted soils.
Both the sealed double ring infiltr
meters and the underdrain lysimet
worked well and gave results that we
consistent with each other.
The laboratory hydraulic conductivi
tests on laboratory compacted spec
mens were poor specific indicators
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10'
O
CM
•s 10-
13
I
u
I
Infiltrometer No. 1
Record
Section
Infiltrometer No. 3
Infiltrometer No. 2'
Infiltrometer No. 4
10
20
30
Time (days)
Figure 1. Field hydraulic conductivity values measured with the record section and
infiltrometers.
Table 1. Summary of Laboratory Hydraulic Conductivity Testing Program for Laboratory-
Compacted Soils
Type Of
Permeameter
Flexible Wall
Fixed Wall
Fixed Wall
Fixed Wall
Fixed Wall
Fixed Wall
Fixed Wall
Fixed Wall
Method of
Compaction
Impact
Impact
Impact
Impact
Kneading
Kneading
Static
Static
Compactive
Effort
Std. Proctor
Std. Proctor
Std. Proctor
Mod. Proctor
Low
High
Low
High
Maximum
Size of Clods'
3/4 in.
314 in.
No. 4 Sieve
3/4 in.
3/4 in.
3/4 in.
314 in.
3/4 in.
Number of
Tests
4
5
4
5
4
4
4
4
'314 in. = 19 mm; No. 4 Sieve = 4.8 mm
field performance. Matching both density
and moisture content, the laboratory tests
underpredict field hydraulic conductivity
by about 100,000 times.
No tests on laboratory-compacted
specimens predicted the performance of
the liner based on correlations with
density alone; in this case they under-
predicted the hydraulic conductivity of
the field liner by about 100 to 100,000
times, based on correlations with density.
It is postulated that laboratory tests can
suggest a minimum density a compacted
soil must exceed to achieve a target
hydraulic conductivity; however, density
tests provide no information on whether a
given construction procedure has pro-
duced or can produce a liner that meets
the "basic objectives" that control field
performance.
With respect to moisture content alone,
the performance of the laboratory tests
ranged from poor to good. Test speci-
mens prepared from large clods using
standard Proctor (ASTM D 698) and
kneading compaction procedures snowed
a strong sensitivity to molding moisture
content and gave hydraulic conductivities
that came relatively close to matching
field performance. The other procedures
underpredicted field performance by as
much as 1,000,000 times.
Laboratory tests on samples taken from
the field liner with 3-in.-diameter (76-mm)
thin-walled tubes underpredicted the
hydraulic conductivity of the field liner by
a factor of about 20,000 times, because:
(1) the paths followed by seepage in the
field had lateral dimensions larger than
the laboratory specimens; (2) taking and
extruding tube samples can densify
unsaturated soils, which can close the
voids that cause high field hydraulic
conductivity, and (3) the spacing between
the voids in the liner provides opportun-
ities for them to not be represented in
laboratory specimens.
Laboratory tests on hand-trimmed
block samples gave results that under-
predicted the hydraulic conductivity of
the liner by only 2 to 10,000 times, which
is better than the performance of thin-
walled tube samples.
The effective porosity of the field liner
was shown to be much less than the total
porosity; the quantity of data collected
was not sufficient to quantify the differ-
ence.
Recommendations
Further research is needed (1) to
assess the performance of various types
of rollers in compacting soil to achieve
low hydraulic conductivity and (2) to
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725
115
I
s
I
>•>
I
105
95
85
8
10
12
14
16
18
20
22
24
Water Content, %
Q Standard Proctor
•f Modified Proctor
X Standard Proctor,
Flexible- Wall Permeameter
4k Standard Proctor,
No. 4 Sieve Clod Size
Note: 3/4-in. (19-mm) maximum clod size was used for all compacted specimens except where
indicated.
Figure 2. Compaction curves for soils compacted with impact compaction.
develop/assess laboratory test methods
for predicting and evaluating the
performance of soil liners.
The full report was submitted in ful-
fillment of Contract No. 68-03-3250 by
McClelland Engineers under the sponsor-
ship of the U.S. Environmental Protection
Agency.
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10-
!
o
io-
10~
10-
10-
O Standard Proctor
• Modified Proctor
X Low-Effort Kneading
O High-Effort Kneading
m Low-Effort Static
•f High-Effort Static
A Standard Proctor.
No. 4 Sieve Clod Size
A Standard Proctor,
Flexible-Wall
Permeameter
—O
I
10
12
14 16
Water Content, %
18
20
22
Note: 3/4-in. (19-mm) maximum clod size and fixed-wall permeameters were used for all
specimens except where indicated.
24
Figure 3. Hydraulic conductivity versus molding water content for all soils compacted in the laboratory, plus field points.
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1
/o-3
c Conductivity, cm/sec
o o q
J, A i
W10
| • | i | i | i | i | i
I •*• £ • Field Points
r « m o A
' O /
* O /
r •
r
[
r
i
O Standard Proctor
+ Standard Proctor,
No. 4 Sieve Clod Size
X Modified Proctor
O Low-Effort Kneading
• High-Effort Kneading
-1- Low-Effort Static
A High-Effort Static
A Standard Proctor,
Flexible- Wall
Permeameter
1 • 1
«
% 0*
X
X X
X
1 1 1 1 1 1 I
70
90 100 110
Dry Unit Weight, Ib/cu ft
120
130
Note: 3/4-in. (19-mm) maximum clod size and fixed-wall permeameters were used for all
specimens except where indicated.
Figure 4. Hydraulic conductivity versus dry unit weight for all soils compacted in the laboratory, plus field points.
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Table 2. Hydraulic Conductivities Measured on Field-Compacted Soil
Location of
Sample
Lower Lift
Lower Lift
Upper Lift
Upper Lift
Lift Interface"
Lower Lift
Upper Lift
Sample
Number
5
6
1
2
-
-
-
Type of Sampler
Thin-Walled Tube
Thin-Walled Tube
Thin-Walled Tube
Thin-Walled Tube
Thin-Walled Tube
Block
Block
Initial Water
Content (%)
16.1
16.7
15.3
17.5
16.4
25.2
25.2
Initial Dry
Unit Weight
(Ib/cu ft)"
113.2
115.3
113.9
113.2
103.7
87.4
91.1
k (cm/sec)
5.0 x JO-9
3.0 x 70-9
2.0 x 10'9
6.3 x 10'10
1.2 x 10-7
7.5 x 10'5
1.1 X JO'8
"100.0 Ib/cu ft = 15.71 kN/cu m.
"Test specimen trimmed for the equivalent of horizontal flow.
All specimens from the liner cell compacted with the roller in the vibratory mode.
Bill R. Elsbury and Gregory A. Sraders are with McClelland Engineers, Inc.,
Houston, TX 76244; David C. Anderson, James A. Rehage, and Joseph A. Sai
are with K. W. Brown & Associates, College Station, TX 77840; and David E.
Daniel is with the University of Texas, Austin, TX 78712.
Jonathan G. Herrmann is the EPA Project Officer (see below).
The complete report, entitled "Field and Laboratory Testing of a Compacted Soil
Liner," (Order No. PB 89-125 9421 AS; Cost: $21.95, subject to change) will be
available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Risk Reduction Engineering Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
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EPA/600/S2-88/067
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