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This is to certify that the
thesis entitled

HYDRAULIC CONDUCTIVITY OF GEOSYNTHETIC CLAY
LINERS PERMEATED AT ELEVATED TEMPERATURES

presented by

NIMISHA H. PATEL

i

LIBRARY
gan State
University

Mich

has been accepted towards furfillment
of the requirements for the

MS. degree in Environmental Engineering

 

J

Milind V. Khire

V Major Professor’s Signature
9/1 3/05

Date

MSU is an Afﬁrmative Action/Equal Opportunity Institution

 

PLACE IN RETURN Box to remove this checkout from your record.
To AVOID FINES return on or before date due.
MAY BE RECALLED with earlier due date if requested.

 

DATE DUE

DATE DUE

DATE DUE

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

2/05 c:/ClRC/DateDue,indd-p.15

 

HYDRAULIC CONDUCTIVITY OF GEOSYNTHETIC CLAY
LINERS PERMEATED AT ELEVATED TEMPERATURES

BY

NINIISHA H. PATEL

A THESIS

Submitted to
Michigan State University
in partial fulﬁllment of the requirements
for the degree of

MASTER OF SCIENCE

Department of Civil and Environmental Engineering

2005

ABSTRACT

HYDRAULIC CONDUCTIVITY OF GEOSYNTHETIC CLAY
LINERS PERMEATED AT ELEVATED TEMPERATURES

By
Nimisha H. Patel

The environmental performance of landﬁll liners is primarily controlled by the fate
and transport of leachate constituents from the landﬁll leachate. Hence, hydraulic
conductivity of the liner is a key factor when selecting material for lining systems.
Hydraulic conductivity is inﬂuenced not only by the properties of the porous media but
also the permeant liquid. There are many studies where elevated temperatures of waste
and leachate have been reported due to the aerobic decomposition of the organic fraction
of waste. At elevated temperatures, soil structure and permeant viscosity change.
However, there is very little experimental data on hydraulic conductivity of clays or
geosynthetic clay liners (GCLs) permeated at elevated temperatures.

The primary objective of this study was to evaluate the effect of elevated permeant
temperature on hydraulic conductivity of GCLs. An experimental setup was designed to
meet the research objectives. The key conclusions are: (1) There is a 2 to 3 fold increase
in the hydraulic conductivity of GCLs when permeated with DI water, tap water, or 0.1
M CaClz solutions at 80 °C when compared at 21 °C; and (2) this increase in hydraulic
conductivity is primarily due to decrease in the viscosity of the permeant. Hence,
hydraulic conductivity of GCLs at elevated permeant temperature can be estimated by
applying the viscosity correction speciﬁed in ASTM D 5084 to the hydraulic conductivity

measured at a room temperature.

To my loving family

iii

ACKNOWLEDGMENTS

At the end of my thesis I would like to thank all those individuals who made this
thesis possible and an enjoyable experience for me. First of all I wish to express my
sincere gratitude to Dr. Milind V. Khire, who guided this work and helped whenever I
was in need. I think his presence at MSU was the best thing that could have happened to
me as it allowed me to hone my skills in multi-disciplinary ﬁelds of geo-environmental
engineering.

I am grateful to the members of my thesis committee, Drs. Shu-Guang Li and Tom
Wolff, for their valuable time and support. I acknowledge the ﬁnancial support extended
to me by the Michigan State University for two semesters in the form of a Research
Assistantship. I am also grateful to Mr. Saradhi Balla and Mr. Kirk Riley for giving me
the opportunity to work as a Research Assistant for two semesters.

Finally, I am thankful to God to have given me my family who stood by me and
will stand by my side to give me support and co-operation forever. I would like to extend
my gratitude to my papa, mummy, Reshma, Falguni and Karishma. I am also thankful to
my friends Ramkumar Subramanian, Rajnish Sharma, Neeraj Kohli, Vaibhav Ekbote,
Monojit Bhattacharya, Gayatri Kuber, Smeeta Bhattacharya, Vandana Yadav and Swati
Shah for their constant encouragement and support. Finally, I would to like to thank my
professors from the Geotechnical department at the Maharaja Sayajirao University and

Geotest house.

iv

TABLE OF CONTENTS

 

 

 

 

 

 

LIST OF FIGURES vii
LIST OF TABLES ix
CHAPTER 1: INTRODUCTION 1
1.1 BACKGROUND .......................................................................................................... 1
1.2 MATERIAL USED FOR LINERS ............................................................................... 4
1.3 GEOSYNTHETIC CLAY LINERS ............................................................................. 5
1.4 TEMPERATURES MEASURED IN MSW LANDFILLS .......................................... 7
CHAPTER 2: FACTORS AFFECTING HYDRAULIC CONDUCTIVITY OF
GCLs 9
2.1 VISCOSITY OF THE PERMEANT ............................................................................ 9
2.2 DOUBLE LAYER THICKNESS ............................................................................... 14
2.3 MINERALOGY OF BENTONITE ............................................................................ 17
2.4 BOUND AND FREE PORE WATER ....................................................................... 18
2.5 PORE PRESSURE INCREASE DUE TO THERMAL EXPANSION ..................... 19
2.6 OTHER FACTORS .................................................................................................... 20
2.6.1 Chemistry of Permeant ...................................................................... 20
2.6.2 Freeze-Thaw and Wet-Dry Cycles ......................................................... 21
2.7 RESEARCH OBJECTIVES ....................................................................................... 24
CHAPTER 3: MATERIALS AND METHODS 26
3.1 MATERIALS .............................................................................................................. 26
3.1.1 Geosynthetic Clay Liner ........................................................................ 26
3.1.2 Hydration and Permeation Liquids ........................................................ 26
3.2 EXPERIMENTAL SETUP ......................................................................................... 30
3.2.1 Permeation System ................................................................................. 30
3.2.2 Temperature Chamber ........................................................................... 32
3.2.3 Sample Preparation ................................................................................ 32
3.2.4 Prehydration ........................................................................................... 36
3.2.5 Termination Criteria for Hydraulic Conductivity Testing ..................... 38
3.2.6 Measurement of Hydraulic Conductivity ............................................... 38
CHAPTER 4: RESULTS AND DISCUSSION 42
4.1 PERMEATION USING DI WATER ......................................................................... 42
4.1.1 GCL ........................................................................................................ 42
4.1.2 Bentonite Extracted from GCL .............................................................. 45
4.1.3 Temperature of Permeant ....................................................................... 45
4.2 PERMEATION USING TAP WATER ...................................................................... 47
4.3 PERMEATION USING CaClz SOLUTION .............................................................. 49
4.4 VISCOSITY CORRECTION ..................................................................................... 55
CHAPTER 5: SUMMARY AND CONCLUSIONS 64

 

 

REFERENCES

vi

Figure l-l:
Figure 1-2:
Figure 1-3:

Figure 2-1:

Figure 2-2:

Figure 2-3:

Figure 2-4:

Figure 2-5:

Figure 3-1:
Figure 3-2:
Figure 3-3:
Figure 3-4:
Figure 4-1:
Figure 4-2:

Figure 4-3:

Figure 4-4:
Figure 4-5:

Figure 4-6:

LIST OF FIGURES

Key components of a typical MSW landﬁll ..................................................... 2
RCRA Subtitle D Liner and LCS ..................................................................... 3
General Conﬁguration of GCLs (Source: CETCO Lining Technologies) ...... 6
Hydraulic Conductivity of GCLs Sequentially Permeated With Tap Water
and Ethanol/Water Mixtures (Mass %) (Source Petrov et al. 1997) .............. 12
Intrinsic Permeability of GCLs Sequentially Permeated With Tap Water and
Ethanol/Water Mixtures (Mass %) (Source: Petrov et a1. 1997) ................... 13

Effect of Prehydration on the Hydraulic Conductivity of a Needle-Punched
GCL Permeated with a Simulated Mine Tailing Solution (Source:

Shackelford et a1. 2000) ................................................................................. 22
Hydraulic Conductivity as a function of Wetting Cycle and Permeant
Chemistry (Source: Lin and Benson 2000) .................................................... 23
Mean hydraulic conductivity of bentonite as a function of permeant
temperature (Source: Cullen et al., 1982) ...................................................... 25
Needle-punched GCL (Bentomat° DN by CETCO) ..................................... 27
Standard Pressure Panel ................................................................................. 31
lOO-mm—diameter Permeameter inside Temperature Chamber ..................... 33
Schematic of the Experimental Set-up ........................................................... 37
Hydraulic Conductivities of GCL for DI water as Permeant ......................... 44
Hydraulic Conductivity of Bentonite for DI water as Permeant .................... 46
Change in Conﬁning Pressure Burette Volume as a function of Temperature

of the Sample Chamber .................................................................................. 48
Hydraulic Conductivity of GCL for Tap water as Permeant ......................... 51
Hydraulic Conductivity of GCL for 0.1 M CaClz Solution as Permeant ....... 54

Change in Viscosity of Water and 0.1 M CaClz Solution as a function of
Temperature ................................................................................................... 56

vii

Figure 4-7: Temperature Correction for Standard Temperature due to Change in
Viscosity of DI water as Permeant ................................................................. 59

Figure 4-8: Temperature Correction for Standard Temperature due to Change in
Viscosity of Tap water as Permeant ............................................................... 61

Figure 4-9: Temperature Correction for Standard Temperature due to Change in
Viscosity of CaClz Solution as Permeant ....................................................... 63

viii

LIST OF TABLES

Table 2-1: Effect of Permeant Temperature on the Unit weight and Viscosity of DI water

......................................................................................................................... l 1
Table 22: Effect of Permeant Temperature on the Dielectric Constant of DI water ....... 16
Table 3-1: Properties of Bentomat” DN GCL .................................................................. 28
Table 3-2: Electrical Conductivity of Permeant Liquids .................................................. 29
Table 3-3: Dynamic Viscosity of DI water and CaClz Solution at the Test Temperatures
......................................................................................................................... 41
Table 4—1: Geometric Mean Hydraulic Conductivities of GCL for DI water as Permeant
......................................................................................................................... 43
Table 4-2: Geometric Mean Hydraulic Conductivities of GCL for Tap water as Permeant
......................................................................................................................... 50
Table 4-3: Geometric Mean of Hydraulic Conductivities of GCL using CaClz Solution as
Permeant ......................................................................................................... 53
Table 4-4: k of GCL Permeated with DI water Corrected for Viscosity .......................... 58
Table 4-5: k of GCL Permeated with Tap water Corrected for Viscosity ........................ 60
Table 4-6: k of GCL Permeated with CaClz Solution Corrected for Viscosity ................ 62

ix

CHAPTER 1

INTRODUCTION

1.1 BACKGROUND

A landﬁll is an engineered containment system, built to isolate waste from the
surrounding environment (groundwater, surface water, and air). The key engineered
components of a municipal solid waste (MSW) landfill are: 1) bottom liner system; 2)
leachate collection system (LCS); 3) gas collection system; 4) capping system and; 5)
surface water management system. Figure 1-1 presents the key components of an MSW
landﬁll.

Liners are designed to create a barrier between the waste and the environment and
to allow efficient drainage of leachate for collection and treatment. Lining systems are
designed according to federal and state regulations. The Federal Resource Conservation
and Recovery Act (RCRA), Subtitle D (1976) regulates MSW landﬁll design,
construction, and operation under Title 40 and Part 258 of the Code of Federal
Regulations According to the US. Federal regulations, a composite liner should consist
of Z 60-cm-thick compacted clay having hydraulic conductivity 5 10'7 cm/sec overlain by
Z 1.5-mm-thick (40 mil) ﬂexible membrane liner (FML) for MSW landﬁlls as shown in
Figure 1-2. Michigan regulations require double composite liner system for MSW
landfills. A double composite liner consists of at least 30-cm-thick sand or gravel
leachate detection layer between the two composite liners. Beyond relevant
environmental regulations, other key considerations for the selection of lining system
include long-term performance, capital cost of construction, and ease of construction.

Compatibility of lining system materials with the chemicals present in the leachate

 

 

Surface Water
Management system

i

Gas Collection System
I"

 

 

Waste

Capping System

J

Lining System and Leachate Collection System

 

Figure l-l: Key components of a typical MSW landﬁll

 

 

LCS Drai
Lay e rn age Geotextile ,

 

    

 

1.5-mm-thick HDPE

Geomembrane 60-cm-thick Compacted Clay

(k s 10'7 cm/s) OR GCL

Figure 1-2: RCRA Subtitle D Liner and LCS

plays an important role in controlling the long-term performance of a lining system.

1.2 MATERIAL USED FOR LINERS

Materials commonly used for construction of liners for waste containment systems
are: l) compacted clay or clay amended with other materials (e.g., ﬂy ash) (Ganti 2004);
2) geomembranes or ﬂexible membrane liners (FMLs); and 3) geosynthetic clay liners
(GCLs). The hydraulic conductivity of compacted clay liners (CCLs) increases in the
presence of some chemicals (Alther et a1. 1985; Anderson et a1. 1985; Keren and Singer
1988; Gleason 1993), due to fractures when it undergoes desiccation, or due to freeze-
thaw cycles (Othman and Benson 1992; Othman et a1. 1994). FMLs are more resistant to
the common chemicals found in MSW landﬁll leachate and are almost impermeable to
water. High Density Polyethylene (HDPE) is the most commonly used material for liners
for MSW landﬁlls.

The environmental performance of a lining system is primarily controlled by the
fate and transport of solute(s) from the landﬁll leachate. Advection and diffusion are the
two key processes that control the fate and transport of solutes from the leachate.
Advection is the migration of solutes that occurs strictly under hydraulic gradients.
Diffusion is the molecular-level migration of solutes that occurs strictly under the
concentration gradient. Dispersion is the mixing and spreading of the contaminant within
the ﬂow system which occurs under the combined inﬂuence of advection and diffusion.
For landﬁll liner applications, for porous materials having relatively high (2 10'5 cm/s)
hydraulic conductivity, advection is the dominant process, while for porous materials
having relatively low hydraulic conductivity diffusion is the dominant mode for solute

transport (Quigley et al.; 1987, Rowe 1987, Shackelford 1989). Hence, hydraulic

conductivity is one of the most important factors that are considered during the material

selection of lining systems and to assess impacts from an existing lining system.

1.3 GEOSYNTHETIC CLAY LINERS

A GCL is a factory-manufactured material consisting of a layer of high swelling
bentonite sandwiched between two geotextiles or glued to a geomembrane (Daniel and
Estomell 1991; Daniel 1991, 1993; Daniel and Boardman 1993; Koemer 1994) (Figure
1-3). The bentonite content by dry mass in a typical GCL is about 5.0 kg/mz. Extensive
usage of GCLs started in 1980s. Since then, GCLs have been extensively used as a
barrier material in many environmental applications including landﬁll liners and covers,
sludge lagoon liners and covers, and secondary containment for underground storage
tanks. GCLs replace or enhance performance of compacted clay layer or geomembranes
in a composite liner setting. Other advantages of GCLs are ease of installation, relatively
low hydraulic conductivity and a greater resistance to meteorological distress (Shan and
Daniel 1991; Boardman and Daniel 1996; Kraus et al. 1997). Most often GCLs are used
in places where supply of good quality natural clay is limited or site conditions are
challenging for constructing a compacted clay liner with adequate construction quality
control and quality assurance.

There are four types of GCLs based on how the bentonite layer is enclosed: (1)
geotextile-enclosed, adhesive-bonded GCL; (2) geotextile-encased, stitch-bonded GCL;
(3) geotextile-encased, needle-punched GCL; and (4) geomembrane-supported adhesive-

bonded GCL.

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Figure 1-3: General Conﬁguration of GCLs (Source: CETCO Lining Technologies)

Typically GCLs use powdered or granular sodium or calcium bentonite. The
thickness of bentonite layer varies from 4.0 to 8.0 mm. GCLs are available in panels
having a minimum width equal to 2.2 to 5.2 by 30 to 60 m length. The following points
list key advantages of GCLs as compared to CCLs:

1. Hydraulic Factors: lower hydraulic conductivity compared to typical CCLs.

2. Physical/Mechanical Issues: better resistance to withstand freeze-thaw and wet-
dry cycles compared to CCLs. Greater shear strength if the strength of the bond
(needle-punch, adhesive, etc) is adequate. Better erosion resistance, and less
potential for cracking from differential settlement.

3. Construction Issues: compared to CCLs, GCL offer superior puncture
resistance, their installation is easier and relatively faster, and the quality of

GCL is more consistent because it is manufactured in a controlled setting.

1.4 TEMPERATURES MEASURED IN MSW LANDFILLS

GCLs are constantly subjected to several stresses in the ﬁeld including thermal
stresses due to the heat generation and heat ﬂow that occurs in natural or engineering
systems such as landﬁlls. Several studies have shown elevated temperatures at the base of
landﬁlls near the leachate collection and lining systems. Collin (1993) has reported
temperatures in excess of 60 °C within landﬁlls. Dach and Jager (1995) measured
temperatures greater than 50 °C at the base of landﬁlls in Germany. Yoshida and Rowe
(2003) monitored three landﬁlls in Japan for 12 to 30 years. They reported temperatures
ranging from 20 to 50 °C near the liners. Age of waste in landﬁll is an important factor to
consider when temperature is monitored. Hanson et a1. (2005) have reported temperatures

in liner system consisting of GCLs ranging from -1 °C to 35 °C for a cell located in the

midwest USA and exposed for a period of more than one year after construction.
Temperatures of a GCL in a landﬁll located in Pennsylvania over a period of 9.5 years
ranged from 20 and 35 °C (Koemer 2001). Rowe (1998) reported temperatures between
10 to 30 °C and 20 to 30 °C for liners containing GCLs located in California and Florida,
respectively. Gartung et al. (1999) monitored temperature variation in a German landﬁll
and reported temperatures greater than 50 °C where the waste was 6 to 8 years old and for
more than 10 years old waste the temperatures were between 20 and 40 °C.

In bioreactor landﬁlls, moisture (leachate or other liquids) and/or air are injected
into the waste to increase the decomposition rate of the waste. Decomposition results in
the settlement of waste which results in an additional volume and it increases the life of
the landﬁll. During the aerobic decomposition process, due to exothermic reactions,
temperatures do increase (Mehta et al. 2001; Hater et al. 2000). Because MSW is a
relatively poor conductor of heat the temperatures in landﬁlls remain elevated until the
waste has completely decomposed. Hater et al. (2000) have reported waste temperatures
between 54 0C to 65 °C in an instrumented bioreactor landﬁll cell located in Kentucky.

Temperatures of leachate collected from recovery wells at a MSW landﬁll in New
York have ranged from 32 °C to 58 °C (Adams and Hullings 2001). Other sites have
recorded leachate temperatures as low as 21 °C. A maximum temperature of about 35 °C
has been recordediin the liner of a bioreactor landﬁll located in California where the
maximum waste temperature reached about 54 °C (Yoho County 2001). In summary, the
temperatures of leachate from MSW landﬁlls that is in contact with the LCS and liner are

typically greater than the room temperature (~ 22 °C). .

CHAPTER 2

FACTORS AFFECTING HYDRAULIC CONDUCTIVITY OF GCLs

The key factors that inﬂuence the hydraulic properties of GCLs are: (1) viscosity
and chemistry of the hydrating and permeant liquids; (2) void ratio or dry unit weight;
and (3) double layer thickness of the clay component. The change in temperature of the
permeating liquid results in these changes: (1) it changes the viscosity of the permeant;
(2) it causes expansion or contraction of the permeant due to change in the temperature
resulting in a change in the void ratio of the clay component; and (3) it can change the
double layer thickness of the clay.

The thickness of the clay double layer is inﬂuenced by the cation concentration in
the solution surrounding the clay particle, the valency of the cations, and the dielectric
constant of the solution. Because change in temperature can change the dielectric
constant, it can change the double layer thickness. Hence, change in the temperature of
the permeant can increase or decrease the hydraulic conductivity of GCLs (Rowe 1998).
In addition, distribution of cations adjacent to charged clay particles which is sensitive to
temperature (Mitchell 1993), can have an effect on the microstructure of the clay. These

key factors affecting hydraulic properties of GCLs are presented in detail in this chapter.

2.1 VISCOSITY OF THE PERMEANT
Relationship between the hydraulic conductivity and properties of soil and
permeating ﬂuid is given by Kozeny-Carman equation (Kozeny 1927; Carman 1937;

Mitchell 1993). Kozeny-Carman equation for the permeability of porous media is given

by Eq. 2-1:

 

l e3 7
= =K—T— 2-1
karzsj (1+e) a, ( )

T

where,

S0 = the wetted surface per unit volume of particles;

T = tortuosity factor;

k0 = pore shape factor;

e = void ratio;

YT = unit weight of the permeant liquid at temperature T;

m = dynamic viscosity of the permeant liquid at temperature T;

k1 = hydraulic conductivity for the permeant liquid at temperature T; and

K = intrinsic permeability of the porous medium.

The effect of permeant properties on intrinsic permeability is accounted for by the
ppm term in Eq. 2-1. Table 2-1 presents the ratio of viscosity to unit weight for
temperatures ranging from 20 to 100 °C. Table 2-1 shows that viscosity and unit weight
decrease as temperature increases. The ratio of viscosity to unit weight decreases slightly
as the temperature increases.

Petrov et al. (1997) permeated GCLs with ethanol and water mixtures and found
that for permeants containing 5 50% ethanol, there is a slight decrease in the hydraulic
conductivity due to an increase in the viscosity of the permeate (Figure 2-1). When the
concentration of ethanol in the permeant was increased to Z 50%, due to signiﬁcant
decrease in the dielectric constant of the permeant, the hydraulic conductivity increased.
By converting the measured hydraulic conductivity into intrinsic permeability, Petrov et
al. (1997) concluded that decrease in the hydraulic conductivity for permeants containing

S 50% ethanol was due to increase in viscosity (Figure 2-2).

10

Table 2-1: Effect of Permeant Temperature on the Unit weight and Viscosity of DI water

 

 

 

 

 

 

Temperature Unit Weight Dynamic Viscosity ply
T(°C) 7(kN/m3) McP) (cP m’IkN)
0 9.79 1.00 0.102
40 9.73 0.65 0.066
60 9.64 0.47 0.048
80 9.53 0.36 0.037
100 9.40 0.29 0.030

 

 

 

 

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«=32mu35kl’a
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U U I

 

 

 

 

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3 10'. \+

o E ‘/\LH _..

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z .

 

 

10-10

0 20 40 so so too
.INITML x ETHANOL m m: PERMEANT

Figure 2-1: Hydraulic Conductivity of GCLs Sequentially Permeated With Tap Writer
and Ethanol/Water Mixtures (Mass %) (Source Petrov et al. 1997)

12

10-11 - __
‘ I ' T V f I r I

Mu. -.-.- 4.25 Ito/ma to 4.54 kg/m’ (1!)
CI = 32 up: to 35 up.

0 reference K. (London up water)
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10-13

 

 

 

10’“

mrnmsnc Penucwiurr. K (cm’)

1’)

o 20 40 so so 100
WNW. at ETHANOL IN THE PERMEANT

 

10.15

 

Figure 2-2: Intrinsic Permeability of GCLs Sequentially Permeated With Tap Water and
Ethanol/Water Mixtures (Mass %) (Source: Petrov et al. 1997)

13

Because temperature of permeant also affects its viscosity, temperature change will result

in a change in the hydraulic conductivity similar to measurements by Petrov et al. (1997).

2.2 DOUBLE LAYER THICKNESS

Changes in the hydraulic conductivity can be qualitatively related to the changes in
the diffuse double layer that surrounds negatively charged particles of clay (Mitchell
1993).

In colloidal chemistry, the adsorbed layer (or diffuse double layer) is commonly
described using the Stem-Gouy model (Gouy 1910; Mitchell 1993; Shackelford 1994;
Shang et al. 1994). According to the model, a thin ﬁlm called “Stern layer” consisting of
oriented water dipoles and ﬁxed hydrated cations is directly adjacent to the clay surface,
while a diffuse layer of hydrated cations attracted to the clay surface resides immediately
adjacent to the Stern layer. The double layer thickness (ta) is given by Shackelford et al.

(2000) as follows (Eq. 2-2).
8.6 .R.T
= J—z..2°.i~2., <24)

8 = dielectric constant of the pore water which is temperature dependent (also

where,

referred to as the relative permittivity);
so = permittivity in a vacuum;

R = Universal gas constant;

F = Faraday’s constant;

T = absolute temperature (°K);

v = valence of the cation; and

14

n = electrolyte concentration.

According to Eq. 2-2, electrolyte concentration, cation valence, and dielectric
constant affect the thickness of the diffuse double layer, which in turn affects the
hydraulic conductivity of bentonite in GCL. Hydraulic conductivity reduces as the
thickness of double layer increases (Mesri and Olson 1971; Shang et al. 1994; Gleanson
et al. 1997; and Stern and Shackelford 1998). On the other hand, reduction in the double
layer thickness results in an increase in hydraulic conductivity which is of great concern
when clays and GCLs are used for environmental barrier applications. When temperature
of the permeant (T) is increased, the dielectric constant of the permeant decreases and
other parameters in Eq. 2—2 stay constant. Hence, when only temperature of the permeant

is changed, the thickness of the double layer can represented by Eq. 2-3.
rd, aJe - T (2-3)

Knowlton (1941) gave the following approximation for calculating dielectric
constant from temperatures 0-100 0C.
8 ~ 80 - 0.4(T — 293) (2-4)
where,

T = absolute temperature (°K).

Table 2-2 presents e and Jr: -T as a function of T for T ranging from 0 to 100 0C

for DI water. Table 2-2 indicates that as T increases, there is a slight decrease in J £-T

which indicates that as the temperature of the permeant (if DI water) increases, there
would a decrease in the double layer thickness which would contribute towards increase

in the hydraulic conductivity of the clay.

15

Table 2-2: Effect of Permeant Temperature on the Dielectric Constant of DI water

 

 

 

 

 

 

 

 

Temperature Temperature Dielectric Constant of Jen—T
T (o C) T (0K) DI water (pF.m'l -°K)
,8 (pF.m'l )

0 273 88 155

20 293 80 153

22 295 79 153

40 313 72 150

60 333 64 146

80 353 56 141
100 373 48 134

 

 

 

 

16

2.3 MINERALOGY OF BENTONITE

The relatively low hydraulic conductivity of GCLs is due to the bentonite it
contains. The mineralogy of the bentonite is an important factor as it partially controls the
hydraulic conductivity. The primary mineral in bentonite clay is montmorillonite
(typically about 70-90% by dry weight). Stern and Shackelford (1998) conducted
experiments on three sand-clay soil mixtures permeated with distilled water. They found
that when the montmorillonite fraction in clay increases, hydraulic conductivity of the
sand-clay mixture permeated with distilled water decreases. Ganti (2004) evaluated the
effect of bentonite content on the hydraulic conductivity of ﬂy ash samples mixed with
bentonite. Ganti (2004) found that as the bentonite content increase, the hydraulic
conductivity of the sample decreases. Thus, overall montmorillonite content of bentonite
is mainly responsible for the low hydraulic conductivity of GCLs (Shackelford et. a1.
2000; Egloffstein 2001).Bentonite in GCLs has a relatively low hydraulic conductivity
due to a relatively small particle size and a relatively thick double layer associated with
montmorillonite (Mesri and Olson 1971).

At elevated temperatures, coagulation and/or the geometric re-arrangement of
particles can take place. Laguros (1969) demonstrated elevated temperatures tend to
change soil structure. The author found that, as temperatures increases, soil particle
disperses due to an increase in the thickness of the diffuse double layer. At low
temperatures, soil structure ﬂocculates due to decrease in the diffuse double layer
thickness. Dispersed clay particles yield a lower hydraulic conductivity compared to

ﬂocculated structure (Mitchell 1993).

17

2.4 BOUND AND FREE PORE WATER

The hydraulic conductivity of GCLs depends upon the fraction of water that is
hydraulically mobile and size and tortuosity of the pathways through which the free water
ﬂows (Mesri and Olson 1971). When the volume of bound water molecules increases, the
fraction of the pore space available for mobile water decreases (for a constant volume of
the soil) and ﬂow paths become smaller and more tortuous. Thus, factors that inﬂuence
the fraction of bound water can impact the hydraulic conductivity of bentonite (McNeal
and Coleman 1966; Egloffstein 1997; Shackelford et al. 2000; Jo et a1. 2001). Likewise,
volume of bound water is affected by temperature, viscosity, cation concentration and
valence, and pH of the permeant solution (Mitchell 1993; McBride 1994; Egloffstein
1995; Petrov and Rowe 1997; Shackelford et al. 2000; Jo et al. 2001; Kolstad et a]. 2004).

A fraction of water present in the pore spaces of bentonite is immobile and the rest
is mobile for a given set of physical and chemical parameters. Mobile water is bulk pore
water that is free to move under a hydraulic gradient, while immobile water is bound to
the external and interlayer mineral surface by strong electrostatic forces within the diffuse
double layer. For a ﬁxed volume of clay, when the volume of bound water molecules
increases, the hydraulic conductivity decreases because the volume available for fraction
of freely ﬂowing bulk water in pore spaces decreases and the cross sectional area of ﬂow
pathways becomes smaller and more tortuous.

The interlayer bound water in bentonite forms in two phases: the “crystalline”
phase and the “osmotic” phase (Van Olphen 1977; McBride 1994; Prost et al. 1998). The
crystalline phase occurs as montmorillonite hydrates from completely dry state. Mineral

surface and cations on the surface continue to hydrate until several monolayers of water

18

molecules are bound within the interlayer. The osmotic phase follows the crystalline
phase, but occurs only when the exchange sites contain monovalent cations (Norrish and
Quirk 1954; Kjellander et al. 1988; McBride 1994; Prost et al. 1998). Osmotic hydration
can result in an appreciable expansion of the interlayer space, a large fraction of water
getting bound in the double layer, and is responsible for a large amount of swelling and
low hydraulic conductivity.

When the interlayer cations are monovalent, as is the case with Na-bentonite, both
crystalline and osmotic hydration occurs, allowing the interlayer spacing to expand
resulting in greater bound water and less volume for mobile water. On the other hand,
when polyvalent cation (e.g., Ca”) is present, a strong electrostatic attraction between
montmorillonite sheets and the interlayer cations prevents osmotic swelling (McBride
1994, 1997; Quirk and Marcelja 1997). Hence, it results in less bound water and more
volume of mobile water resulting in a greater hydraulic conductivity. In monovalent
solutions, the volume of swelling and interlayer spacing is inversely proportional to the
square root of the concentration of the solution (Norrish and Quirk 1954; McBride 1994;

Zhang et al. 1995; Onikata et al. 1999).

2.5 PORE PRESSURE INCREASE DUE TO THERMAL EXPANSION

The increase in temperature of the permeant results in an increase in the pore water
pressure because volumetric expansion of the pore water is greater than void space of the
mineral solids (Eq. 2-2). Because of the relatively low hydraulic conductivity of the
bentonite, longer time is required for this pore pressure to dissipate. In saturated soils,
change in temperature generates changes in volume and/or effective stress. Thermal

expansion of mineral solids and pore water is caused by temperature increases. Equation

19

2-5 presents the variables that control the change in pore pressure as a result of increase
in temperature for soils.

__ n(a, - aw )AT + aSTAT
m

V

 

Au (2-5)

where,
Au 2 change in pore water pressure;
n = porosity;
(131 = physicochemical coefﬁcient of structural volume change;
or, = thermal expansion coefﬁcient of cubical expansion of mineral solids;
(1,, = thermal expansion coefﬁcient of soil water;
AT = change in temperature; and

m, = compressibility of the soil structure.

2.6 OTHER FACTORS
2.6.1 Chemistry of Permeant

Double layer thickness of clay particles is governed by Eq. 2-2. According to Eq. 2-
2 these properties of permeant liquid can expand or shrink the double layer and hence
cause can decrease or increase the hydraulic conductivity of the clay: (1) dielectric
constant; and (2) concentration and valency of cations (e.g., 0.1 M versus 1 M, Na+
versus Ca”).

Jo et al. (2001) evaluated the effect of concentration and valence of cations in
single—species salt solution on swelling and hydraulic conductivity of non-prehydrated
GCLs. The authors found that the hydraulic conductivity of GCLs increases with: (1) the

valency of the cations at a given concentration; and (2) the concentration for a given

20

 

 

valency. In addition, the authors found that the effect of valency on the hydraulic
conductivity is greatest at moderate concentrations (i .e, 0.025 — 0.1 M).

Daniel et a1. (1993), Shackelford (1994), Didier and Comeaga (1997), Gleason et
a1. (1997), Petrov and Rowe (1997), Stern and Shackelford (1998), and Lin (1998) show
that the order of permeation of bentonite has a signiﬁcant effect on the ﬁnal hydraulic
conductivity. Hydrating bentonite with DI water before permeation with chemical
solution or leachate results in a lower hydraulic conductivity than direct permeation with
the chemical solution. Figure 2-3 depicts that the hydraulic conductivity of the GCL
specimen prehydrated using DI water stabilized at around 7 x 10'9 cm/s, whereas ﬁnal
hydraulic conductivity of the non-prehydrated specimen remained signiﬁcantly higher at

around 9 x 1045 cm/s.

2.6.2 Freeze-Thaw and Wet-Dry Cycles

Hewitt and Daniel (1997) proved in their experiments that GCLs can withstand at
least three freeze-thaw cycles without considerable change in hydraulic conductivity.
Because landﬁll leachate contains dissolved salts, use of salt solution as the permeant is
more representatives (Lin and Benson 2000).

Lin and Benson’s (2000) experiments showed an increase in hydraulic conductivity
to as high as 7.6 x 1045 cm/sec within 3 to 6 wetting cycles, when GCLs were permeated
with 0.0125 M CaClz solution (Figure 2—4). Erickson et al. (1994) published ﬁeld
performance of GCLs after one winter of freeze-thaw at a location near Milwaukee,
Wisconsin. There is very little published ﬁeld data of effect of freeze-thaw on hydraulic

conductivity of GCLs.

21

 

 

 

 

 

 

 

 

 

 

.-Ir-—-— -*
10'. .-;7;4A Alli-A “ 7

O 2 4 5 . 3 10 12 14

 

wvo‘e'e' w-r" 0
3 o O . . . 1
E. 10" - ----~- -~ .
5. 1
IE * ‘
‘8 10-7 L + Prehydrated .
é , -O- Non-Prehydrated .
g L
.3 10" L
'5
a
I-
'5
>.,
:

Pore Volume of Flow

Figure 2-3: Effect of Prehydration on the Hydraulic Conductivity of a Needle-Punched
GCL Permeated with a Simulated Mine Tailing Solution (Source: Shackelford et al.
2000)

22

10'3

 

 

 

 

 

 

 

A
1'
g 10--
Q
.2
‘g’ 10"
"D
=
o
o
.2 10"
'5
a
r.
'3.
= 10"
1040 l r r L“ 1 J I l

 

o 1 2 a 4 s s' 7 a
Number of Wetting Cycles

Figure 24: Hydraulic Conductivity as a function of Wetting Cycle and Permeant
Chemistry (Source: Lin and Benson 2000)

23

Cullen et al. (1982) conducted research related to the effect of elevated permeant
temperature on the hydraulic properties of these three clay minerals: Georgia kaolinite,
Urbana illite, and bentonite. The authors used water as the permeant and the hydraulic
conductivity test was conducted on a sample having dimension equal to 10.12 cm
diameter and a height of 2.54 cm, constant rate of strain consolidation method was used
to measure the hydraulic conductivity. Figure 2-5 presents the hydraulic conductivity of
bentonite at permeant temperatures equal to 20, 90, and 160 °C. Figure 2-5 shows that
there

is a slight decrease in the hydraulic conductivity at 90 °C followed by a 4-fold increase at

160 °C.

2.7 RESEARCH OBJECTIVES

All mechanical properties, hydraulic properties, and ﬂuid transport characteristics
of GCLs are typically determined at room temperature (~ 22°C) in the laboratory.
However, temperature of leachate in MSW landﬁlls where GCLs are commonly used in
the lining system is rarely 20 °C. The data presented in this chapter suggests that
temperature of permeant can inﬂuence the hydraulic conductivity of GCLs which will
impact the rate of leakage of contaminants from landﬁlls. Hence, the primary aim of this
study is to evaluate the effect of elevated permeant temperature on the hydraulic
conductivity of GCLs. Another objective of this study was to determine which property is
critical to predict the change in hydraulic conductivity of GCLs when permeant

temperature is increased.

24

 

49.5

 

 

.3»
°;
:3 8
U m
«8 B
C
00
U!-
.2 '2
«3 " 12.5 3.3
‘0
I
* 20 * 90 160

Temperature, degrees C

Figure 2-5: Mean hydraulic conductivity of bentonite as a function of permeant
temperature (Source: Cullen et al., 1982)

25

 

CHAPTER 3

MATERIALS AND METHODS

To evaluate the hydraulic conductivity of GCLs at elevated temperatures of landﬁll
leachate, a series of tests at temperatures ranging from the room temperature (~ 22 °C) to

80 to 100 °C were conducted.

3.1 MATERIALS
3.1.1 Geosynthetic Clay Liner

The geosynthetic clay liner (GCL) used for this study was Bentomat® DN
manufactured by CETCO. The following description is based on the information
provided by 'CETCO. This GCL contains chemically untreated sodium bentonite
encapsulated between a two nonwoven geotextiles, which are needle-punched together.
The maximum hydraulic conductivity reported by the manufacturer for the GCL tested in

this study is 5 x 10'9 cm/sec at room temperature for DI water (Table 3-1).

3.1.2 Hydration and Permeation Liquids

The liquids used in the experiments to hydrate and permeate the GCL samples
consisted of de-aired deionized water (DI water), MSU tap water, and 0.1 M calcium
chloride (CaClz) solution in DI water. Electrical conductivity of these liquids is presented
in Table 3-2.

Calcium chloride solutions having 0.001 M, 0.01M and 0.1 M concentrations were
prepared by dissolving CaClz (manufactured by IT Baker) in DI water. Measured
electrical conductivity (EC) at 25 0C for 0.001 M, 0.01 M and 0.1 M concentration are

given in Table 3-2. CaClz solution of 0.1 M concentration was selected as a permeant

26

Non-woven geotextile

Granular bentonite

 

Non-woven geotextile Needle punched ﬁbers

Figure 3-1: Needle-punched GCL (Bentomat® DN by CETCO)

27

Table 3-1: Properties of Bentomat® DN GCL

 

 

 

 

 

 

 

 

 

Material Property Test Method Required Values
Bentonite Swell Indexl ASTM D 5890 24 ml/2g min.
Bentonite Fluid Loss] ASTM D 5891 18 ml max.

Bentonite Mass/Area” ASTM D 5993 0.75 lb/ftz (3.6 kg/mr) min.
GCL Index Flux"3 ASTM D 5887 1 x 10'8 m3/m2/sec max.
GCL Hydraulic ASTM D 5887 5 x 10'9 cmlsec max
Conductivity"3

Liquid Limit" ASTM D 4318 360 %

Plastic Limit“ ASTM D 4318 55 %

Uniﬁed Soil ASTM D 2487 CH

Classiﬁcation4

 

 

 

Manufacturer provided listed properties.

Bentonite mass/area reported at 0% moisture content.

Index ﬂux and permeability testing with deaired distilled/deionized water at 80 psi (551 kPa) cell
pressure, 77 psi (531 kPa) headwater pressure and 75 psi (517 kPa) tailwater pressure. Reported
values are equivalent to 925 gal/acre/day. This ﬂux value is equivalent to a permeability of 5x10'9
cmlsec for typical GCL thickness, Actual ﬂux values vary with ﬁeld condition pressures.

Test performed for current study.

28

Table 3-2: Electrical Conductivity of Permeant Liquids

 

 

DI Tap 0.001 M 0.01 M 0.1 M
water water CaCl; CaClz CaClz
Electrical conductivity (“S/cm) 0.6 792 225 1,640 13,800

 

 

 

 

 

 

29

because it closely represents the ionic strength of typical MSW landﬁll leachate
(Schroeder et al., 2001). Table 3-2 shows that MSU tap water is relatively “hard” having

equivalent salt concentration in the range of 0.001 to 0.01 M CaClz solution.

3.2 EXPERIMENTAL SETUP
3.2.1 Permeation System

There are open and closed permeation systems that are commonly used for
hydraulic conductivity testing of soils. An open system implies that the inﬂuent and/or
efﬂuent reservoirs of the system are open to the atmosphere or are connected to
compressible ﬂuid pressure sources (e. g., pressurized air). Burette systems operating with
compressed or atmospheric air and ﬂow pump systems can be classiﬁed as open system
(Wang and Benson 1999). In an open system, a saturated sample can change in volume
by expelling or absorbing permeant liquid from the inﬂuent and efﬂuent burettes during
permeation (Figure 3-2). A closed system uses a closed loop of liquid to permeate the
soil. This is achieved by connecting the inﬂow and outﬂow drainage lines of the
permeameter with a mercury capillary tube.

For this study, a 1-D consolidation permeameter manufactured by Trautwein
Geotechnical Testing was used. It is a rigid wall permeameter. The permeameter was
developed for measuring the hydraulic conductivity of remolded samples of soft soil,
slurry backﬁll material, and grout. In this setup, the sidewall leakage problem during
GCL testing is alleviated by using an appropriately high conﬁning stress and a bentonite
seal around the perimeter of the sample. In the l-D consolidation permeameter, the

sample undergoes consolidation along vertical direction.

30

4..
5.. a. ...

i. 0

e

.4444»;

t. rﬁﬁﬂﬂﬁﬂ

4444

“enaem4444444L

- 1n .. .. ad . ..
inhumane...
so...

weave.

J

:43 _

w.

...

w.

 

Figure 3-2: Standard Pressure Panel

31

In order to tolerate the elevated temperatures during testing and to maintain
corrosion resistance during CaClz permeation, the base and top plates, the sample sleeve,
and valves of the permeameter were made of stainless steel. The tubes connected to the
permeameter cell were made up of Nylon 6 manufactured by Dayco and was able to
resist temperatures up to 105 °C. The O-rings were made up of nitrile rubber.
TRAUTWEIN Standard Panel M100000 was used to apply the desired hydraulic gradient
and also apply back pressure to the sample. A photograph of the panel is presented in

Figure 3-2.

3.2.2 Temperature Chamber

To measure hydraulic conductivity at elevated temperatures, Model TMVH—5
temperature chamber manufactured by BMA (Bryant Manufacturing Associates) was
used. This model is a low/high temperature humidity control chamber having internal
dimensions equal to 2.3 m by 2.3 m by 2.9 m (Figure 3-3). It is designed to generate and
control temperatures ranging from -17 °C to +200 0C. For temperature control, it
incorporates a two-channel fully automatic microprocessor program. The temperature is
raised by nichrome wire heaters on ceramic cores and a mechanical refrigeration system
lowers the temperature. The power requirements are 208 or 220 V, 1 PH (1 Phase), 60
HZ. A photo of the lOO-mm-diameter sample cell in the temperature chamber is

presented in Figure 3-3.

3.2.3 Sample Preparation
The GCL samples tested were cut out form an intact roll of GCL stored in the

laboratory. The sample preparation procedure presented by Daniel et al. (1997) was

32

i

‘3 .f
ﬁat-’9.

 

Figure 3-3: IOO-mm-diameter Perrneameter inside Temperature Chamber

33

followed. The procedure consisted of:

1. Marking the sample outline for the desired diameter of the sample to be cut
from the GCL roll. It was done by placing a porous stone having the diameter
equal to that of the sample. GCL specimen having lOO-mm-diameter (4 inch)
was used for DI water and CaClz permeation. Because the 100-mm diameter
cell was occupied, a 71-mm—diameter (2.8 inch) cell was used for tap water
permeation;

2. The GCL was cut by a sharp utility knife along the outer edge of the porous
stone;

3. A small quantity of the hydration liquid (DI water, or tap water, or CaClz
solution) was sprinkled on the edge of the sample with a squirt bottle to allow
local hydration of the bentonite along the edge of the sample to minimize clay
loss during transport of the sample to the permeameter cell;

4. Loose geotextile ﬁbers were trimmed with a pair of sharp scissors. In case any
bentonite fell out from the edges of the sample, bentonite paste (bentonite mixed
with the hydration liquid) was lightly added between the geotextiles;

5. The initial weight of the GCL specimen was measured to the nearest 0.1 g. The
initial thickness of the GCL specimen was measured to the nearest 0.1 mm with
a vemier caliper. Total ﬁve measurements were carried out and the average
value was used for the estimation of hydraulic conductivities;

6. Bentonite paste was applied along the circumference of the GCL specimen to

prevent sidewall leakage when the sample was placed in the permeameter cell;

34

7. The lower saturated porous stone was placed in the recess in the base. The
sample mould was cleaned, and the prepared GCL sample was placed;

8. Checked that the O-ring at the base is in place and free from dirt. A thin layer of
vacuum grease was applied to the O-ring to avoid any possible leakage.
Vacuum grease was applied at the bottom and top of the mould, the mould with
sample was placed on top of the base. Greased piston was slide down to the top
of the porous stone above the GCL sample. The top drain lines remain attached
to the top cap;

9. The piston and top cap were placed on the sample mould. Care was taken not to
crimp the top drains, when putting the top cap on the sample mould. The piston
mould was twisted a little so that slots in the top place are aligned with those in
the base. Clamping rods were inserted and tightened evenly with all the valves
open. After tightening of clamping rods all the valves were closed;

10. A line between the “cell” burette and brass elbow ﬁtting located on the top cap
of the permeameter were connected. Similarly a line between the “tail” burette
and valve located on the top cap of the permeameter were also connected
(Figure 3-4). The diameter of all tubes connected to the head and tail burette
were 3 m (1/8 in). A connection between the “head” burette and one of the
valves on the base of the permeameter was made;

11. Tube length to the bottom of sample was kept long enough (1 m in this case) so
that the residence time of permeant liquid was 2 2 hrs throughout the duration
of the test for hydraulic conductivities of the sample S 10'8 cm/s for the

hydraulic gradients applied during the tests. Hence, the permeant liquid attained

35

12.

13.

14.

desired temperature before it permeated through GCL sample. The length of the
tube carrying the permeant that has already ﬂown through the GCL (efﬂuent)
was the approximately equal to the inﬂuent tube to cancel out the evaporation
loss (a detailed discussion is presented in Chapter 4);

All burettes were ﬁlled with the permeant liquid. “Tail” and “Head” connection
valve were opened. Conﬁning, bottom and top pressures were applied.

The sample was hydrated for 48 hrs as per ASTM D 5084. During hydration of
the sample no hydraulic gradient was applied on the sample. The sample was
allowed to saturate under no ﬂow condition using back pressure (prehydration is
described in detail in Section 3.2.4);

After the sample was hydrated, hydraulic conductivity tests were started
on the sample by applying a hydraulic gradient at temperatures of the permeant
ranging from ~ 21 °C to 100 °C. The temperature was not increased until the
termination criteria speciﬁed in ASTM D 5084 was met (termination criteria are
presented in detail in Section 3.2.5); and
After the completion of the hydraulic conductivity tests, the permeameter cell
was carefully opened and the GCL specimen was retrieved for the measurement

of ﬁnal height, wet weight, and water content.

3.2.4 Prehydration

Prehydration allows hydration and swelling of GCL specimen prior to permeation

(ASTM D 5084). For current study, the three GCL samples tested were hydrated with the
liquid used for permeation (DI water, tap water or 0.1 M CaClz solution). Prehydration

was carried out by soaking the GCL specimen in the permeameter with permeant liquid

36

Head Water

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Pressure Burette
Tail Water
Pressure Burette
Temwatm Conf'ming Pressure ————-‘
Chamber Burette
Standard Pressure Panel
Conﬁning
Pressure Inlet
Stainless
Steel
Cylinder
Stainless
Steel
Piston
Porous Stones
Stainless
of Permeant C onfming
Pressure
Chamber Tube
(Length ~ 0.5m)

Influent P011 Tube Efﬂuent Port '1th
(Length ~ 1m) (Length ~ 1m)

Figure 3-4: Schematic of the Experimental Set-up

37

 

for 48 hrs under no net hydraulic gradient as suggested by Ruhl and Daniel (1997). Each
of GCL specimens was saturated and consolidated using a backpressure of 482.6 kPa
(70.0 psi) and an effective vertical conﬁning pressure of 69 kPa (10 psi) for a 48-hr
period. After 48 hours of hydration, as per ASTM D 5084-Method C, the sample was
subjected to a hydraulic gradient equal to approximately 180 to 270 to measure the
hydraulic conductivity. The gradient used is in the same range as reported by Lee et. al.,
(2005); Ruhl and Daniel (1997) and Lin and Benson (2000). The hydraulic gradient was
applied by increasing the pressure of the inﬂuent reservoir to 434 kPa (63 psi) and
maintaining the backpressure at 414 kPa (60 psi). Shackelford et. al. (2000) showed that
the use of higher hydraulic gradients does not signiﬁcantly inﬂuence the hydraulic

conductivity of GCLs.

3.2.5 Termination Criteria for Hydraulic Conductivity Testing

The termination criteria speciﬁed in ASTM D 5084 was followed. This criteria
requires: (1) a minimum of four hydraulic conductivity measurements must be made; 2)
the ﬁnal four consecutive hydraulic conductivity measurements must all fall within 0.75
to 1.25 times the geometric mean of the four hydraulic conductivity measurements; 3) the
ratio of inﬂow to outﬂow must fall between 0.75 and 1.25 for the four hydraulic
conductivity measurements; and 4) no upward or downward trend should exist in the four

hydraulic conductivity measurements.

3.2.6 Measurement of Hydraulic Conductivity
Hydraulic conductivity tests were conducted in accordance with ASTM D 5084-

Method C. Falling head rising tail tests were carried out to measure the hydraulic

38

conductivity. In falling head rising tail tests, readings of burettes connected to the bottom,
top and conﬁning pressure chamber of the sample were taken periodically throughout the
test. Using Eq. 3-1, hydraulic conductivity values were calculated for two consecutive
readings. Once termination criteria were satisﬁed for last four consecutive readings, the
temperature was increased to 40, 60, 80 and 100°C and the test was repeated for each
temperature.

ASTM D 5084 gives the following equation (Eq. 3-1) for the calculation of

hydraulic conductivity, k for falling head rising tail test.

k: “raw'L ln—h-L (3-1)
(am +aw).A.At h2

 

where,
k = hydraulic conductivity;
an. = cross-sectional area of the reservoir containing the inﬂuent;
a0... = cross-sectional area of the reservoir containing the efﬂuent;
A = cross-sectional area of GCL specimen;
L = height of GCL specimen;
At = interval of time over which the head difference across the sample changes from
h] to hz;
t1 = time at the start of the permeation trial;
t2 = time at the end of the permeation trial;
h1 = head loss across the specimen at t; in the units of height of water; and

h2 = head loss across the specimen at t; in the units of height of water.

39

ASTM D 5084 speciﬁes a viscosity correction for hydraulic conductivity if the test
temperature was other than 20 °C. The correction converts the hydraulic conductivity to

measurement at 20 °C. This correction is viscosity-based (Eq. 3-2).

1., = it, (3-2)
#20

where,

kzo = hydraulic conductivity corrected to 20°C;

1120 = dynamic viscosity of water at 20°C;

in = dynamic viscosity of water at test temperature, T; and

k1 = hydraulic conductivity at test temperature, T.

The viscosity of water depends on temperature. At 293 °K (20°C), the viscosity of
water is 1.002 CF. The viscosity decreases as temperature increases. The dynamic

viscosity of DI water and 0.1 M CaClz solution at the temperatures used in this study are

presented in Table 3-3.

40

Table 3-3: Dynamic Viscosity of DI water and CaClz Solution at the Test Temperatures

 

 

 

 

 

 

 

 

 

 

 

Permeant Liquid Temperature Dynamic Viscosity
T (°C) 11(10'3 N.slm2)

DI waterr 20 1.004

40 0.658

60 0.475

80 0.365

100 0.294
0.1 M CaClz 20 1.4
Solution2 40 1.0
60 0.7
80 0.5
100 0.4

 

 

 

Source: ' CRC handbook chemistry and physics
2 Perry’s Chemical Engineers Handbook

41

CHAPTER 4

RESULTS AND DISCUSSION

This chapter presents the results which consisted of the hydraulic conductivities of
the GCL samples measured at temperatures ranging from the room temperature to about
100 °C for these three permeants: (1) DI water; (2) Tap water”, and (3) 0.1 M CaClz

solution in DI water.

4.1 PERMEATION USING DI WATER
4.1.1 GCL

The hydraulic conductivities of the GCL specimen at 22, 40, 60, 80 and 100 °C
measured during the test are plotted in Figure 4-1 along with cumulative pore volumes
(PV) permeated through the sample. The geometric mean of hydraulic conductivities is
presented in Table 4-1. The room temperature in the laboratory ﬂuctuated between 21
and 22 °C.

Figure 4-1 and Table 4-1 indicate that k of the GCL increased as the temperature of
the permeant was increased. It can be observed in Figure 4-1 that as soon as the
temperature of the temperature chamber was increased, within less than 30 min, there
was an increase in the k value followed by a smaller decrease. This initial increase in the
k was an apparent increase due to the expansion of the tubes connecting the sample
carrying the inﬂuent and efﬂuent and the specimen cell. After the tubes were fully
expanded, the permeant ﬂow continues through the sample as it approaches steady-state
when the effect of expansion of the inﬂuent and efﬂuent tubes and the specimen cell does
not inﬂuence the k value. As explained in Chapter 3, because the inﬂuent and efﬂuent

tubes are

42

Table 4-1: Geometric Mean Hydraulic Conductivities of GCL for DI water as Permeant

 

 

 

 

 

 

Temperature Duration to Cumulative Geometric krl kg;
of the Reach Pore Mean
Permeant Termination Volume Hydraulic
T(°C) Criteria PV (cm’) Conductivity
t ((1) k1 (cm/s)

22 13.7 1.2 2.6E-09 (kg) 1.00
40 12.0 2.0 3.0E—09 1.15
60 6.2 2.8 4.2E-09 1.60
80 6.0 3.8 5.2E-09 2.00
100 8.9 5.8 6.5E-09 2.50

 

 

 

 

 

43

Hydraulic Conductlvlty, Hem/sec)

10"3

 

 

 

 

 

 

Cumulatlve Elapsed Time, t (hr)

Figure 4-1: Hydraulic Conductivities of GCL for DI water as Permeant

I I 1 l I I I | r T I 1 r r r I r 1 r 1 f l 15
- Permeant and Hydrating Liquid = DI water 0 f
' Sam le Diameter = 100 mm «a. "
” P 3 323113.; " q
. 1 Pore Volume = 42.4 cm ..~' 9, :2, 5 12
9
- 6
— 3
i 1 i 1 i i i 1 i i i 1 1 i 1 l i i i 1 i i i o
0 200 400 600 800 1000 1200

Pore Volume, PV (cm’)

identical in length and cross section, any evaporative or diffusive loss from the tubes
cancels out and does not inﬂuence the k value at steady-state. Note that once the sample
has met the termination criteria as per ASTM D 5084 (Method C), we have assumed that
the ﬂow has reached steady-state. The PV data plotted in Figure 4-1 and summarized in
Table 4-6 indicates that the rate of ﬂow of the permeant gradually increased as the
temperature was increased. This is due to the increase in the k of the GCL. . Water

content of the GCL sample at the end of test was 121%.

4.1.2 Bentonite Extracted from GCL

Hydraulic conductivity of bentonite extracted from the GCL was also measured
using DI water as permeant to isolate the effect of needle punched ﬁbers in the GCL and
to conﬁrm the increase in k values presented in Figure 4-2 due to increase in the permeant
temperature. Figure 4-2 presents the k of the bentonite for temperatures of DI water
increased from 22 to 95 °C followed by a decrease in temperature from 95 to 5 °C and
increase in temperature 5 to 22 °C. Figure 4-2 shows a similar increase in hydraulic
conductivity of bentonite with increase in the temperature of DI water as seen for the
GCL in Figure 4-1. When temperature of the permeant was reduced, the k of the
bentonite decreased and reached about the same value for the corresponding temperature.
It was also observed that for a given temperature, the hydraulic conductivity of the

bentonite (Figure 4-2) is slightly less than the GCL (Figure 4-1).

4.1.3 Temperature of Permeant
Figure 4-3 shows the change in the volume of the conﬁning pressure burette

recorded for the GCL permeated using DI water at temperatures of the permeant ranging

45

Hydraulic Conductivity, Hem/sec)

 

IIII

 

 

’Perine'arit and Hydrétingiiou'id '= in water.
Sample Diameter = 100 mm ~

—

 

 

 

 

 

 

 

 

 

 

10'9 7““ ' ' "'d
[ "-. W>\ """ ;
------- k x075
W0
22°C <—> 22 C .
10°C .
o 5°C 3
10-10ittliiilmuiluuilitnliiuli 1
0 200 400 600 800 1 000 1 200 1400
Cumulative Elapsed Time, 1 (hr)
Figure 4-2: Hydraulic Conductivity of Bentonite for DI water as Permeant

46

from 22 °C to 100 °C. Figure 4-3 shows that as the temperature of the sample chamber is
increased, the corresponding burette records increase in the volume as the permeant
conﬁned in the conﬁning pressure chamber of the permeameter (Figure 3-4) undergoes
expansion. Once the expansion is complete, the burette reading stays about the same.
Figure 4-3 also shows that greater the chamber temperature, greater the volume of
expansion of the permeant conﬁned in the conﬁning pressure chamber of the
permeameter. Figure 4-3 also shows that it took about 240 minutes for the permeant in
the conﬁning pressure chamber of the permeameter to reach the temperature maintained
outside the permeameter in the temperature chamber.

The minimum length of the inﬂuent and efﬂuent tubes presented in Figure 3-4 was
designed on the basis of the data presented in Figure 4-3. The length of the inﬂuent tube
was equal to 1 m to allow a minimum of 240 minutes of residence time for the permeant
in the inﬂuent tube to reach the temperature of the chamber maintained outside the

permeameter before it enters the GCL.

4.2 PERMEATION USING TAP WATER
Because the lOO-mm—diamter permeameter was occupied, for measuring k of the
GCL using tap water as the permeant, a 71-mm-diameter permeameter was used. Tap
water was used to hydrate as well as permeate the sample. Because tap water contains
dissolved salts, it had a greater electrical conductivity (Table 3-2) compared to DI water.
The geometric mean of hydraulic conductivities of the GCL specimen at 22, 40, 60,
and 80 °C measured during the test are summarized in Table 4-2 and plotted in Figure 4-

4. Cumulative pore volumes permeated through the sample are also plotted in Figure 4-4.

47

 

Burette Volume, (cm’)
$

Change in Conflnlng Pressure

0 x",

A
V

 

u‘

A
V

Permeant and
- Sample Diameter = 100 mm

1

A
v

Hydrating Liquid = DI water

A
V

s"

I I I I I I I

 

22 °C 0

Temperature of the
Sample Chamber
4O °CEl———E1

60 °Ce—m

80 °C‘9
- 100 °Cs
r 1 I I

c»

 

 

J

 

240 360 480

Elapsed Time, t (min)

Figure 4-3: Change in Conﬁning Pressure Burette Volume as a function of Temperature
of the Sample Chamber

48

The geometric mean hydraulic conductivities are presented in Table 4-2. During the test
at 100 °C, the specimen cell developed a leak. Hence, we were not able to measure the k
of the GCL for tap water permeant at 100 °C. Figure 4-4 and Table 4-2 show that the k
value of the GCL increases as the temperature of the permeant increases. The k values of
the GCL at room temperature and the increases in the k values at elevated temperatures
for tap water and DI water are about the same (T ables 4-1 and 4-2).

The PV data plotted in Figure 4-4 and summarized in Table 4-2 indicates that the
rate of ﬂow of the permeant gradually increased as the temperature was increased. This is
due to the increase in the k of the GCL. Water content of the GCL sample permeated

using tap water at the end of the test was 134%.

4.3 PERMEATION USING CaClz SOLUTION

Because a MSW landﬁll leachate contains salts, Lin et al. (2000) and others have
permeated salt solutions through GCLs to evaluate the effect on its k. The key ﬁndings of
these studies have been: (1) appreciable increase in the k of the GCL if it is hydrated and
permeated with salt solutions having concentration 2 0.1 M; and (2) greater the valency
of the cations of the salt, the greater the increase in k. Hence, in this study, we permeated
the GCL using 0.1 M solution of CaClz and evaluated the effect at temperatures ranging
from the room temperature to 80 °C. The GCL was hydrated using the CaClz solution
prior to its permeation. In order to maintain the residence time of the permeant in the
inﬂuent tube at greater than 4 hrs (Figure 4-3) and allow the temperature of the permeant
to reach the temperature of the surrounding chamber before it enters the GCL, the length
of the inﬂuent tube was increased to 100 m. The hydraulic conductivities of the GCL

specimen at 22, 40, 60, and 80 °C measured during the test are plotted in Figure 4-5 along

49

Table 4-2: Geometric Mean Hydraulic Conductivities of GCL for Tap water as Permeant

 

 

 

 

 

Temperature Duration to Cumulative Geometric k1] kg;
of the Reach Pore Volume Mean
Permeant Termination PV(cm°) Hydraulic
T (°C) Criteria Conductivity
t (d) k1 (cm/s)
22 9.5 1.2 2.3E—09 (kg) 1.00
40 3.2 1.7 3.0E-09 1.30
60 9.9 3.4 3.4E-09 1.47
80 3.4 4.3 4.6E-09 2.00

 

 

 

 

 

50

Hydraulic Conductivity, Hem/sec)

10"

1 0‘9

 

" Sample Diameter = 71 mm
_1PV = 18.8 cm°

 

 

"—IP"'I"'EI"" "
' Permeant and Hydrating Liquid = Tap water

I I

ITM I I I

 

 

 

 

PV (cm’)

1 L I l l I

 

I l l I

 

0 1 00 200 300

400

500

Cumulative Elapsed Time, t (hr)

Figure 44: Hydraulic Conductivity of GCL for Tap water as Permeant

51

600

14
10.5
6..
E
3
>
7 O.
o“
E
2
. §
3.5 9
u°

with cumulative PVs permeated through the sample. Geometric mean hydraulic
conductivities are presented in Table 4-3. During the test at 100 °C, the inﬂuent tube
severely clogged due to CaClz precipitation. Hence, we were not able to measure the k of
the GCL for CaClz permeant at 100 °C. Such precipitation was relatively small at
temperatures 5 80 °C.

Data presented in Figure 4-5 and Table 4-3 indicates that the k of GCL increased
with the temperature of the permeant similar to that for when the GCL was permeated
using DI and tap waters (Figures 4-1 and 4-4). However, as found by Lin et al. (2000)
and others, the k of the GCL at a given temperature of the permeant was about 3 orders of
magnitude more than the k values when permeated with DI and tap waters. Figure 4-5
shows that initially, at 22 °C, the k of the GCL ﬂuctuated greatly. This may have occurred
due to the replacement of Na+ cations from N a-bentonite in the GCL with Ca” from the
permeant. Once chemical equilibrium was potentially approached, the ﬂuctuation in the
values of k decreased (Figure 4-5). The PV data plotted in Figure 4-5 and summarized in
Table 4-3 indicates that about 190 PVs of CaClz solution were permeated through the
sample during the test lasting several days. Because k values of the GCL when permeated
by CaClz solution are about 3 orders of magnitude greater than the k values DI and tap
water permeation, the PVs for CaClz permeation were signiﬁcantly more. Water content

of the GCL sample permeated with CaClz solution was 129%.

52

Table 4-3: Geometric Mean of Hydraulic Conductivities of GCL using CaClz Solution as

 

 

 

 

 

Permeant
Temperature Duration to Cumulative Geometric le km
of the Reach Pore Mean
Permeant Termination Volume Hydraulic
T (°C) Criteria PV cm° Conductivity
t (d) kr (cm/s)
22 20 117 9.55E-07 (kzz) 1.00
40 6.9 145 1.18E-06 1.24
60 7.55 178 1.76E-06 1.84
80 2.0 189 2.49E-06 2.61

 

 

 

 

 

53

 

 

 

 

 

 

10'5 . . . r . . . . . . .. 4 r . . . . , 550
_ Permeant and Hydrating Liquid = 0.1 M CaCl2 Solution
A .4 Sample Diameter = 100 mm.
g {3. 1 Pore Volume = 42.4 cm33 440
5. ‘~ ‘ “g
g E
1: ..
g E
:1
o .—
o
.3 >
§ <———22 °c———> g
'D K _ 1 10 a
5:. Pore Volume
7 (9M
1 0' i l i i i I i i i l i i i l o
0 200 400 600 800

Cumulative Elapsed Time, t (hr)

Figure 4-5: Hydraulic Conductivity of GCL for 0.1 M CaClz Solution as Permeant

54

4.4 VISCOSITY CORRECTION

Petrov et al. (1997a) have demonstrated that change in viscosity of the permeant
can inﬂuence the hydraulic conductivity of clays. Figure 4-6 presents the viscosity of DI
water and 0.1 M CaClz solution as a function of temperature (Perry 1984; CRC 1992).

Figure 4-6 shows that viscosity of water and the salt solution decreases as its
temperature is increased. ASTM D 5084 provides an equation for viscosity correction to
convert the k measured at a laboratory temperature to 20 °C (Eq. 3-2). In this study, we
have applied this correction to all k values of the GCLs measured at various temperatures
for the three permeants. This correction was applied to normalize the effect of the change
in viscosity of the permeant due to the change in its temperature. Intrinsic permeability of
GCLs was also evaluated to isolate the effect of change in viscosity and unit weight of

the permeant. Intrinsic permeability was calculated using Eq. 4-1:

k, = K31 (4-1)

where,

Yr = unit weight of the permeant liquid at temperature T;

“.7 = dynamic viscosity of the permeant liquid at temperature T;

k1 = hydraulic conductivity for the permeant liquid at temperature T; and

K = intrinsic permeability of the porous medium.

Table 4-4 and Figure 4-7 present the geometric mean k of the GCL measured at
various temperatures for DI water as permeant, k corrected as per Eq. 3-2 to temperature
of permeant at standard temperature of 20 °C (kzo), and the intrinsic permeability (K) of

the GCL calculated using Eq. 4-1.

55

 

 

 

 

1.6 _ . , . , , I I
«g 1.4 l i
z' 3 :

1.2 — d
92 _ .
3: 1 l <— CaCl2 Solution 2
E C ‘
3 .
o 0.8 —
.2 .
>
u _
E 0.6 :-
G
c .—
5‘ 0.4 —

0.2 b

o

 

Temperature, T (°C)

Figure 4-6: Change in Viscosity of Water and 0.1 M CaClz Solution as a function of
Temperature

56

An analysis of variance (ANOVA) conducted on the kzo and K values presented in
Table 4-4 and Figure 4-7 indicates that the corrected values of k are equal or drawn from
the populations with the same mean. Thus, the increase in k observed in response to the
increase in the temperature of DI water used as permeant is primarily due to the decrease
in the viscosity of the permeant.

A similar viscosity correction was applied to k values of the GCL measured for tap
water and 0.1 .M CaClz solution used as permeants. The corrected values of k and
estimated values of K are presented in: (1) Table 4-5 and plotted in Figure 4-8 for the tap
water; and (2) Table 4-6 and plotted in Figure 4-9 for the CaClz solution. An ANOVA
analysis conducted on the corrected k and K values presented in Tables 4-5 and 4-6 also
indicated that the data are equal or belong to populations having the same mean. Thus,
the increase in k observed in response to the increase in the temperature of tap water or
0.1 M CaClz solution used as permeants is primarily due to the decrease in the viscosity
of the permeants.

It is beyond the scope of this study to quantify the effect of possible change in the
double layer thickness or clay structure as suggested by Eq. 2-2 on the k values for the
temperatures of the permeants tested. However, because corrected values of k and
estimated K are statistically the same, the increase in k observed in response to the
increase in the temperature of the permeants was primarily driven by decrease in the

viscosity of the permeants

57

Table 44: k of GCL Permeated with DI water Corrected for Viscosity

 

 

 

 

 

 

 

Temperature of Geometric Mean of Intrinsic
the Permeant k values Corrected k at 20 °C Permeability

T (°C) k“, (cm/s) ‘ k2, (cm/s) K (cm’)

22 2.57E-09 2.47E-09 2.53E—10

40 2.95E-09 1.93E-09 2.00E-10

60 4. l7E-09 1.97E-09 2.05E-10

80 5.23E—09 1.9OE-09 2.00E-10

100 6.51E-09 1.90E-09 2.03E-10

 

 

 

 

58

Intrinsic Permeability, K

EB

Measured k

VA

3 Corrected k at 20 °c

 

            

wwwuwmmm.
........
.u.u.u.u.vu.n.u
30.0.3055... I p r

   

 
    

 

 

    

 

 

 

 

Q
P\
a T.
.m w
W U
-I % m
r
a w m
@
.m k m
[U h
Mm .-
-Mm m
..m% e
m1 m
-m__ a
.Yr P
H.”
-d
nm
-am
-MD
.em
mm
.ea
PSle
a. w
0 0 .0
1

C5. v. :50 3 3:33.58 22......

:0
332.3 c. Joe .0 23.82.50 2323:

Temperature Correction for Standard Temperature due to Change in

Figure 4-7

Viscosity of DI water as Permeant

59

Table 4-5: k of GCL Permeated with Tap water Corrected for Viscosity

 

 

 

 

 

Temperature of Geometric Mean of Intrinsic
the Permeant k values A Corrected k at 20 "C Permeability

T (°C) k", (cm/s) k2. (cm/s) K (cm’)

22 2.27E-09 2.18E-09 2.23E-10

4O 3.02E-09 1.98E-09 2.04E-10

60 3.44E-09 1.62E-09 1.69E-10

80 4.59E-09 1.67E-09 1.75E-10

 

 

 

 

6O

Intrinsic Permeability, K

E

Measured k

7A

 

 

 

 

 

 

Ir
6
t
-a
W
-w
FT
.—
.w
TG.
my Um
ovgm
2 .m1
m 5
-Wr
m Hm
wide.
an
.ah
.MD
a
are”
m
rm
Tea
PS
mu m. .0:
..O. m .0

r53 x Joe 3 53853.“. 22......

mo
AocoEoI Joe 3 33.5%:8 2.323:

  

Permeant Temperature, T (°C)

in

Temperature Correction for Standard Temperature due to Change

ty of Tap water as Permeant

Figure 4-8

rscosi

V

61

Table 4-6: k of GCL Permeated with CaClz Solution Corrected for Viscosity

 

 

 

 

 

Temperature of Geometric Mean of Intrinsic
the Permeant k values Corrected k at 20 ”C Permeability

T (°C) km (cm/s) k2. (cm/s) K (cm’)

22 9.55E—07 9.55E-07 1.36E-07

4O 1.18E-06 8.49E-07 1.22E-07

60 1.76E-06 8.83E-07 1.28E-07

80 2.49E-06 8.90E-07 1.3OE-07

 

 

 

 

62

Measured k B Intrinsic Permeability, K

Q Corrected kat 20 °c
10'5
Permeant and Hydrating Liquid = 0.1 M CaCl Solution

Sample Diameter = 100 mm

on
intrinsic Permeability of GCL, K (cm’)

Hydraulic Conductivity of GCL, k (cmlsec)

 

10'7
22 40 60 80
Permeant Temperature, T (°C)

Figure 4-9: Temperature Correction for Standard Temperature due to Change in
Viscosity of CaClz Solution as Permeant

63

CHAPTER 5

SUMMARY AND CONCLUSIONS

In this study, the effect of elevated permeant temperature on the hydraulic
conductivity of GCLs was evaluated. GCL consisting of untreated sodium bentonite
sandwiched between needle-punched non-woven geotextiles was permeated with DI
water, tap water, and 0.1 M CaClz solution in three separate experiments. During each
experiment, the GCL sample was hydrated using the permeating liquid for 48 hours at
room temperature followed by permeation to measure hydraulic conductivity at
temperatures increased in 20 °C steps starting at the room temperature (~20 to 22 °C) to
100 °C. The ASTM speciﬁed termination criteria were met before the temperature was
increased during each test cycle. Based on the experimental data, the following
conclusions were drawn.
1. Elevated temperature of all permeant liquids (e.g., DI water, tap water and
CaClz solution) resulted in an increase in the hydraulic conductivity of the GCL;

2. Viscosity correction applied to the hydraulic conductivities measured at various
temperatures for the three permeants indicated that corrected k at 20 °C is about
the same for all temperatures tested for a given permeant. In addition, for all
three permeants, there is about three-fold increase in k at 80 °C when compared
to k at 20 °C. Thus, decrease in the viscosity of the permeant when the
temperature of the permeant is increase is the primary reason for the increase in
the k of GCLs at elevated temperatures of permeant; and

3. Structural changes in the clay due to the change in the double layer properties

can also inﬂuence the k. Because, for a given permeant, intrinsic permeabilities

64

calculated from the k values measured at various temperatures were about the
same, it can be concluded that increase in permeant temperature does not result
in structural changes of the clay or the changes are relatively small and hence do
not inﬂuence k.

4. Hydraulic conductivity of GCLs at an elevated design temperature can be
estimated by applying the viscosity correction speciﬁed in Eq. 3-2. The
correction consists of multiplying the k value of the GCL measured at the room
temperature by the ratio of the dynamic viscosities of the permeant at the room
temperature to that at the elevated design temperature.

The key practical implication of this study is that landﬁll designers need to take the
liner temperature into consideration when designing or investigating liners consisting of
GCLs. Relatively simple viscosity correction can be used to estimate the hydraulic
conductivity at the design temperature when GCL-speciﬁc hydraulic conductivity data

for the design temperatures do not exist.

65

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