This document summarizes a study on using bentonite-silt mixtures as seepage barriers in landfill liner systems. Standard proctor tests were conducted on silt samples stabilized with 3-15% bentonite by weight. For both silts, maximum dry density increased and optimum moisture content decreased with higher bentonite content. Permeability tests found that permeability decreased significantly for both silts as bentonite content increased, reducing permeability by over 99% in some mixtures. The study demonstrates that bentonite addition can improve the compaction and decrease the permeability of silts for use as landfill liner materials.

1. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
(Print), ISSN 0976 – 6316(Online) Volume 4, Issue 2, March - April (2013), © IAEME
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UTILIZATION OF BENTONITE-SILT MIXTURES AS SEEPAGE
BARRIERS IN LINER SYSTEMS OF ENGINEERED LANDFILLS
Nitish Puri1
and Deepak Soni2
1
(Assistant Professor, Department of Civil Engineering, GCET, Greater Noida, Uttar Pradesh, India)
2
(Assistant Professor, Department of Civil Engineering, GIMT, Kurukshetra, Haryana, India)
ABSTRACT
The permeability and compaction characteristics of several bentonite-silt mixtures
were determined and effects of bentonite content on the above stated characteristics were
investigated. Standard proctor test were conducted on both silts and silts stabilized with 3, 6,
9, 12 and 15% of bentonite clay by weight. For both type of silts values of MDD increases
and OMC decreases with increase in percentage of bentonite as an additive. To ensure
consistent performance of these clay liners, they were compacted to maximum dry density
(MDD) by adding optimum moisture content (OMC). Falling head permeability test were
conducted on compacted plastic and non-plastic silt samples stabilized with 3, 6, 9, 12 and
15% % of bentonite clay by weight. The permeability values for all silt-bentonite mixtures
were measured. A Significant decrease in values of permeability was observed for both types
of silt-bentonite mixtures with increase in percentage of bentonite clay as an additive.
Keywords: Permeability, compaction, clay liners, bentonite, maximum dry density and
optimum moisture content
1. INTRODUCTION
Modern landfills are engineered containment systems, designed to minimize the
impact of solid waste (refuse, trash, and garbage) on the environment and human health. In
modern landfills, the waste is contained by a liner system. The primary purpose of the liner
system is to isolate the landfill contents from the environment and, therefore, to protect the
soil and ground water from pollution originating in the landfill. The greatest threat to ground
water posed by modern landfills is Leachate. Leachate consists of water and water-soluble
compounds in the refuse that accumulate as water moves through the landfill. This water may
be from rainfall or from the waste itself. Leachate may migrate from the landfill and
contaminate soil and ground water, thus presenting a risk to human and environmental health.
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2. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976
(Print), ISSN 0976 – 6316(Online) Volume 4, Issue 2, March
Landfill liners are designed and constructed to create a barrier between the waste and th
environment and to drain the Leachate
prevent the uncontrolled release of
low permeability are often used as seepage barriers in liner systems o
When such types of clays are unavailable
high plastic imported clays or commercially available clays such as bentonite to achieve
mixtures of desired values of permeability. Coeffici
can be 10-8
cm/sec or less and having a thickness of 100 cm or more
two silty soils of plastic and non-
bentonite clay to reduce their permeability.
2. LITERATURE REVIEW
2.1 General
Waste is a by-product of human activity that cannot be put to any use. The term
waste’ refers to waste that is solid.
It can be dry moist or wet and it remains at the location where it is deposited.
waste is dumped on open ground, it causes the following environmental problems:
a) Ground water contamination through seepage of Leachate into the ground.
b) Surface water contamination through erosion of fine particles of waste as well as
Leachate run-off from sides of dump.
c) Local air contamination due to fugitive dust, gaseous emissions,
bad odour.
d) Other problems like increase in rodents and pests,
garbage/dry leaves/plastics. Bird menace to overhead air
blockage of surface water drainage paths due to alteration of natural topography
area.
These harmful effects of waste dump can be minimized
that is, by isolating it from the environment.
liner at the base of the waste and an impermeable cover at the top of the waste
waste disposal facility as shown in
Fig.2.1 Schematic drawing of an engineered landfill.
International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976
6316(Online) Volume 4, Issue 2, March - April (2013), © IAEME
347
Landfill liners are designed and constructed to create a barrier between the waste and th
Leachate to collection and treatment facilities. This is done to
prevent the uncontrolled release of Leachate into the environment. Compacted clays having
low permeability are often used as seepage barriers in liner systems of engineered landfills.
unavailable then in-situ soils must be treated with medium to
high plastic imported clays or commercially available clays such as bentonite to achieve
mixtures of desired values of permeability. Coefficient of permeability for seepage barriers
cm/sec or less and having a thickness of 100 cm or more [6]. In the present study,
-plastic nature have been stabilized with small percentages of
e their permeability.
product of human activity that cannot be put to any use. The term
waste’ refers to waste that is solid.
It can be dry moist or wet and it remains at the location where it is deposited.
waste is dumped on open ground, it causes the following environmental problems:
Ground water contamination through seepage of Leachate into the ground.
r contamination through erosion of fine particles of waste as well as
off from sides of dump.
Local air contamination due to fugitive dust, gaseous emissions, wind-blown
Other problems like increase in rodents and pests, risk of fire from burning
garbage/dry leaves/plastics. Bird menace to overhead air crafts, slope failures and
blockage of surface water drainage paths due to alteration of natural topography
These harmful effects of waste dump can be minimized by containing the solid waste,
that is, by isolating it from the environment. This can be done by providing an impervious
liner at the base of the waste and an impermeable cover at the top of the waste [7]
as shown in Fig. 2.1 below is called as landfill.
Schematic drawing of an engineered landfill. Source: Bonaparte et al. (2002)
International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
IAEME
Landfill liners are designed and constructed to create a barrier between the waste and the
to collection and treatment facilities. This is done to
Compacted clays having
f engineered landfills.
situ soils must be treated with medium to
high plastic imported clays or commercially available clays such as bentonite to achieve
ent of permeability for seepage barriers
In the present study,
been stabilized with small percentages of
product of human activity that cannot be put to any use. The term ‘solid
It can be dry moist or wet and it remains at the location where it is deposited. When solid
waste is dumped on open ground, it causes the following environmental problems:
Ground water contamination through seepage of Leachate into the ground.
r contamination through erosion of fine particles of waste as well as
blown litter and
risk of fire from burning
, slope failures and
blockage of surface water drainage paths due to alteration of natural topography of the
by containing the solid waste,
This can be done by providing an impervious
[7]. This solid
Source: Bonaparte et al. (2002)

3. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
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2.2 Requirements
The most critical component of a liner or a cover is the impervious barrier. Such a
barrier is expected to meet the following requirements:
a) It should be impervious and should behave monolithically over several hundred
square metres of land areas.
b) It should be flexible and remain intact under settlement of subsoil or of waste.
c) It should be durable for the design life of landfill.
d) It should be strong enough to withstand stresses imposed by filled wastes and by
vehicles moving on it.
Clay meets most of the requirements of a barrier layer. Table 2.1 shows required
characteristics of clay liners.
Characteristics Clay liner
Thickness 0.6 – 1.5 m
Permeability 10-8
m/sec or less
Density MDD determined as per tests
Moisture content OMC determined as per tests
Shear strength UCS determined as per tests
Table 2.1 Requirements for a good clay liner
Note: First two parameters are considered important for clay liners.
3. MATERIALS
3.1 Bentonite clay
It was collected from Laxmi Lining Material Pvt. Ltd, Opposite Royal Palace, Sodal Road,
Preet Nagar, Jalandhar – 144004. It is classified as clay of high compressibility, CH, as per
classifications of IS: 1498 (1970) [3]. Its physical and engineering properties are reported in
Table 3.1.
3.2 Silt
Two types of silts were collected, one from village Ramdaspur and other from village Ajnala
of District Amritsar. Both silts were classified as silt of low compressibility, ML, as per
classifications of IS: 1498 (1970) [3]. There physical and engineering properties are reported
in Table 3.1.

4. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
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Characteristics
Materials
Silt I Silt II Bentonite
Specific gravity (G) 2.71 2.7 -
Atterberg’s
limits
LL 22 25 265
PL NP 19 46
PI NP 6 219
Compaction
characteristics
MDD (g/cc) 1.62 1.82 -
OMC (%) 14.9 13.2 -
Colour Brown Light Brown Yellow
Classification
Silt of low
compressibility
Silt of low
compressibility
Clay of high
compressibility
Group ML ML CH
Grain size
distribution
Clay 0% 15% 88%
Silt 87% 66% 12%
Sand 13% 19% 0%
Unconfined compressive
strength (UCS) in kg/cm2 1.02 0.92 -
Table 3.1 Characterization of materials
4. EXPERIMENTAL INVESTIGATION
A series of falling head permeability test were conducted on bentonite-silt mixtures to
evaluate their performance as a clay liner in landfills. These tests were performed as per the
specifications of IS: 2720 (Part 17) (1966) [5]. Standard proctor tests were conducted on silts
and silts stabilized with 3, 6, 9, 12 and 15% of bentonite by weight. These tests were
conducted in order to prepare specimens at maximum dry density by adding desired optimum
moisture content as per specifications of IS: 2720 (Part 7) (1974) [4].
4.1 Moisture-density relationships
Standard Proctor tests have been conducted to determine optimum moisture content
(OMC) and maximum dry density (MDD) of silts stabilized with various varying percentages
of bentonite clay. Fig 4.1(a) and Fig 4.2 (b) show comparison of MDD and OMC for silts
stabilized with bentonite clay and these values are reported in Table.4.1.
For silt I, MDD and OMC were observed as 1.62 g/cc and 14.9% respectively. For silt II,
MDD and OMC were observed as 1.82 g/cc and 13.2 % respectively. For silt I stabilized
with bentonite MDD varies from 1.62 to 1.73 g/cc and OMC varies from 14.9 % to 13.42 %.
It has been observed that for silt I MDD increases and OMC decreases with increase in
percentage of bentonite as an additive. For silt II MDD varies from 1.82 g/cc to 1.91 g/cc and
OMC varies from 13.2% to 12.43%. Also for silt II, it has been observed that MDD increases
and OMC decreases with increase in percentage of bentonite as an additive.

5. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
(Print), ISSN 0976 – 6316(Online) Volume 4, Issue 2, March - April (2013), © IAEME
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Table 4.1 Values of MDD and OMC for bentonite-silt mixtures
Fig. 4.1 (a) Variation of MDD vs. Percentage of bentonite as an additive
Fig. 4.1 (b) Variation of OMC vs. Percentage of bentonite as an additive
4.2 Permeability characteristics
For silt I and silt II permeability has been observed as 5.5 x 10-6
cm/s and 2.96 x 10-7
respectively. For bentonite-silt I mixtures permeability varies from 5.5 x 10-6
cm/s to 1.07 x
10-8
cm/s. Hence total reduction in permeability was 99.81 %. It has been observed that
permeability decreases significantly with increase in percentage of bentonite as stabilizer. For
bentonite-silt II mixtures permeability varies from 2.96 x 10-7
cm/s to 0.91 x 10-8
cm/s.
Which means total reduction in permeability was 99.69 %.
1.6
1.65
1.7
1.75
1.8
1.85
1.9
1.95
0 5 10 15 20
Maximumdrydensity(MDD)ing/cc
Percentage of bentonite as stabilizer (%)
Silt I
Silt II
12
12.5
13
13.5
14
14.5
15
15.5
0 5 10 15 20
Optimummoisturecontent(%)
Percentage of bentonite as stabilizer (%)
Silt I
Silt II

6. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
(Print), ISSN 0976 – 6316(Online) Volume 4, Issue 2, March - April (2013), © IAEME
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Table 4.1 Values of permeability (k) in cm/sec for bentonite-silt mixtures
Sample
Percentage of bentonite as an additive
0% 3 6 9 12 15%
Silt I
+
Bentonite
5.5 x 10-6
2.3 x 10-6
7.8 x 10-7
6.1 x 10-7 2.97 x 10-
8 1.07 x 10-8
Silt II
+
Bentonite
2.96 x 10-7 1.02 x 10-
7 9.8 x 10-8
8.7 x 10-8
4.7 x 10-8
9.1 x 10-9
Fig.4.2 Variation of permeability (K) with percentage of bentonite as additive
Fig. 4.2 Variation of permeability with percentage of bentonite as an additive
5. CONCLUSIONS
The study demonstrates the influence of bentonite clay on the permeability and
compaction characteristics of locally available silts. The following conclusions have been
drawn based on the laboratory investigations carried out in this study:
1. For both type of silts values of MDD increases and OMC decreases with increase in
percentage of bentonite as an additive. Which means better compaction can be
expected from these silt-bentonite mixtures. Similar results reported by other
investigators.[1]
2. A Significant decrease in values of permeability was observed for both types of silt-
bentonite mixtures with increase in percentage of bentonite clay as an additive.
3. Silt-bentonite mixtures containing silt II performed well as compared to mixtures
containing silt I. Hence it is recommended that plastic silts in combination with
bentonite should be used as clay liners if available.
0.00E+00
1.00E-06
2.00E-06
3.00E-06
4.00E-06
5.00E-06
6.00E-06
0 5 10 15 20
Permeability(k)incm/s
Percentage of bentonite as an additive (%)
Silt I
Silt II

7. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308
(Print), ISSN 0976 – 6316(Online) Volume 4, Issue 2, March - April (2013), © IAEME
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4. Percentage of bentonite should be maintained between 10 to 15 % because beyond
that extent further improvement in permeability is not possible and also not
economical. Similar results were reported by other investigators.[2]
5. It is also recommended to use locally available clays similar to bentonite if present.
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