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USE OF FLY ASH AS AN ALTERNATIVE LANDFILL LINER
MATERIAL
Submitted in partial fulfillment of the requirements for the degree of
MASTER OF TECHNOLOGYIn
GEOTECHNICAL ENGINEERING
By
Soumyadip Chowdhury
Under the guidance of
Dr. Anil Kumar Mishra
Department of Civil Engineering
INDIAN INSTITUTE OF TECHNOLOGY GUWAHATI
Guwahati 781039, India
July 2011
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Certificate
This is to certify that the project work entitled Use of Fly ash as an Alternative Liner
Materialbeing submitted by Mr. Soumyadip Chowdhury(Roll No. 09410441), for the partial
fulfillment of the requirement for the award of Master of Technology is a record of bonafide
work carried out under my supervision. The content of this project work has not been submitted
to any other institute or university for award of any degree.
Dr. Anil Kumar Mishra
Assistant ProfessorDepartment of Civil Engineering
Indian Institute of Technology, Guwahati
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Acknowledgement
I would like to express my sincere gratitude and hearty thanks to my advisor Dr. Anil Kumar
Mishra for his guidance, encouragement and gracious support throughout my work. His vast
knowledge and expertise in soils has motivated me to do my best and for that, I am forever
grateful. And his support at every stage proved very much helpful in successful completion of
this work.
My thanks are due to all faculty members, laboratory staff of civil engineering especially Mr.
Upadhay who has helped me a lot for doing experiments in the laboratory.
I am also thankful to all my friends for their kind co-operation and specially, Mr Srikant
Vadlamudi, Mr Pawan Kumar Shah, Mr Pravudatta Pradhan and Mr Amol Shivdas. Without
their charming company, my small endeavor could not have been so pleasurable.
I am indebted a lot to my parents for their whole hearted moral support and constant
encouragement towards the fulfillment of the degree and throughout my life. Above all, its the
most gracious and the most merciful Almighty God for his help to enable me to complete this
research work.
Soumyadip Chowdhury
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Abstract
Landfill liners are used for the efficient containment of waste materials generated from different
sources. In the absence of impermeable natural soils, compacted mixtures of expansive soil and
sand have found wide applications as landfill liners. It is to be noted that, in case, these materials
are not locally available, the cost of the project increases manifold due to its import from
elsewhere. Also, sand has become an expensive construction material due to its limited
availability. With this in view, the present study attempts to explore a waste material such as fly
ash as a substitute for sand. The major objective of this study is to maximize the use of fly ash
for the said application. Different criteria for evaluating the suitability of material for landfill
liner have been studied in this study. However, further investigations are required with different
source of fly ash and alternative material to generalize the findings.
Keywords: Landfill liner, Design criteria, Fly ash, Cement, Bentonite, Hydraulic conductivity,Compressibility
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TABLE OF CONTENTSPage No.
CERTIFICATE 2ACKNOWLEDGEMENT 3
ABSTRACT 4
CONTENT 5
LIST OF FIGURES 7
LIST OF TABLES 8
Chapter-1: Introduction 9
1.1.1. Prevention and Reduction 9
1.1.2. Recycling 9
1.1.3. Composting 10
1.1.4. Sanitary Landfilling 11
1.2. Containment System 12
Chapter-2 14
2.1. Types of Liner 14
2.1.1. Single Liner 14
2.1.2. Single Composite 15
2.1.3. Double Liner 15
2.1.4. Double Composite Liner 15
2.2. Design Criteria for Landfill Liner 16
2.2.1. Standard Design 17
2.2.1. Alternative Design 17
2.2.3. Equivalent Design 18
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2.2.4. Arid Design 18
2.3. Selection of Liner Material 18
2.4. Type of Landfill Liner Material 20
2.4.1. Bentonite Liner 20
2.4.2. Asphalt Liner 20
2.4.3. Soil Asphalt Liner 21
2.4.4 Soil Cement Liner 22
2.4.4.1. Dry Mix Soil Cement 23
2.4.4.2. Plastic Soil Cement Mix 23
2.5. Necessity for the Requirement of a Alternative Liner Material 24
Chapter-3 28
3.1. Materials 28
3.2. Method 28
3.2.1. Consolidation Test 28
3.3. Determination of hydraulic conductivity and compressibility 31
Chapter-4 33
4.1 General 33
4.1.1. Compaction properties of the mixtures 33
4.1.2. Hydraulic Conductivity 34
4.1.3. Compressibility 35
4.1.4. Co-efficient of consolidation 38
4.2. Scope of future Work 38
5.0. References 39-40
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LIST OF FIGURES
Fig. No. Name Page No.
Fig.1. Cross section of different liner system 11
Fig. 2. Acceptable water content and dry density for compacted soil 13
Fig.3. Relation between void ratio and hydraulic conductivity for the 34
three mixtures
Fig.4. Relation between void ratio and over burden pressure for the three 36
mixtures
Fig.5. Relation between pressure and co-efficient of compressibility 37
Fig.6. Relation between coefficient of consolidation and over burden 39
pressure for the three mixtures
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LIST OF TABLE
Table No. Name Page No.
Table 1. Past research and Result 26-27
Table 2. OMC and MDD values of fly ash- cement mix with 33
different proportion
Table 3. Values of compression index and expansion index 31
Table 4. Classification of Potential Expansion of Soils Using EI 38
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Chapter-1
1.1 INTRODUCTION
The high population and rapid industrialization in the last few decades have led to the generation
of huge quantities of hazardous wastes, which have further aggravated the environmental
problems in the country by depleting and polluting natural resources. Therefore, rational and
sustainable utilization of natural resources and its protection from toxic releases is vital for
sustainable socio-economic development. Indias garbage generation stands at 0.2 to 0.6
kilograms of garbage per head per day. Also, it is a well known fact that land in India is scarce.
There are several methods of treatment and disposal of solid waste-
1.1.1. Prevention and Reduction:
The best method of managing waste is prevention and reduction, which can be achieved in a
number of ways like recycling and making use of second-hand items.
1.1.2. Recycling:
Recycling involves processing used materials (waste) into new products to prevent waste of
potentially useful materials, reduce the consumption of fresh raw materials, reduce energy usage,
reduce air pollution (from incineration) and water pollution (from land filling) by reducing the
need for "conventional" waste disposal, and lower greenhouse gas emissions as compared to
virgin production. Recycling is a key component of modern waste reduction and is the third
component of the "Reduce, Reuse, and Recycle" waste hierarchy. Recyclable materials include
many kinds of glass, paper, metal, plastic, textiles, and electronics. Although similar in effect,
the composting or other reuse of biodegradable waste such as food or garden waste is not
typically considered recycling. Materials to be recycled are either brought to a collection center
or picked up from the curbside, then sorted, cleaned, and reprocessed into new materials bound
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for manufacturing. In a strict sense, recycling of a material would produce a fresh supply of the
same material, for example; used office paper would be converted into new office paper, or used
foamed polystyrene into new polystyrene. However, this is often difficult or too expensive
(compared with producing the same product from raw materials or other sources), so "recycling"
of many products or materials involve their reuse in producing different materials (e.g.,
paperboard) instead. Another form of recycling is the salvage of certain materials from complex
products, either due to their intrinsic value (e.g., lead from car batteries, or gold from computer
components), or due to their hazardous nature (e.g., removal and reuse of mercury from various
items).Some disadvantages are-
a) It is a very expensive procedure.b) Some waste cannot be recycled.c) Technological know-how is very essential for this process.d) Separation of useful material from waste is very difficult job.
1.1.3. Composting:
Compost is composed of organic materials derived from plant and animal matter that has been
decomposed largely through aerobic decomposition. Organic matter constitutes 35%-40% of the
municipal solid waste generated in India. This waste can be recycled by the method of
composting. The process of composting is simple and practiced by individuals in their homes,
farmers on their land, and industrially by cities and factories. The compost itself is beneficial for
the land in many ways, including as a soil conditioner, a fertilizer, addition of vital humus or
humic acids, and as a natural pesticide for soil. In ecosystems, compost is useful for erosion
control, land and stream reclamation, wetland construction, and as landfill cover. The process
occurs naturally and is a critical component to soil health. After plants and animals die, bacteria
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go to work decomposing the remains. Once the decay process is complete, the original matter is
no longer recognizable and a rich, dark, soil-like substance remains. The living organisms
involved in the decay process thrive in an environment of the right combination of air, water,
nitrogen, and carbon. The better the conditions, the faster the compost process. Composting of
organic materials from the solid waste stream not only provides a valuable benefit to nutrient
deficient soils, but also reduces the amount of waste that ends up in landfills or incinerators.
Other benefits of composting organic matter include the increase in beneficial soil organisms
such as worms and centipedes, suppression of certain plant diseases, the reduced need for
fertilizers and pesticides, prevention of soil erosion and nutrient run-off, and assistance in land
reclamation projects. Material resulting from the composting of bio-solids and yard waste is used
primarily as an organic soil conditioner and partial fertilizer. It is applied to agricultural lands,
recreational areas such as parks and golf courses, mined lands, highway medians, cemeteries,
home lawns and gardens.
1.1.4. Sanitary Land filling:
The term "sanitary landfill" was first used in the 1930s to refer to the compacting of solid waste
materials. Initially adopted by New York City and Fresno, California, the sanitary landfill used
heavy earth-moving equipment to compress waste materials and then cover them with soil. The
practice of covering solid waste was evident in Greek civilization over 2,000 years ago, but the
Greeks did it without compacting. Sanitary landfills involve well-designed engineering methods
to protect the environment from contamination by solid or liquid wastes. A necessary condition
in designing a sanitary landfill is the availability of vacant land that is accessible to the
community being served and has the capacity to handle several years of waste material. In
addition, cover soil must be available. Today, the sanitary landfill is the major method of
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disposing waste materials in India and other developed countries, even though considerable
efforts are being made to find alternative methods, such as recycling, incineration, and
composting. Among the reasons that landfills remain a popular alternative are their simplicity
and versatility. For example, they are not sensitive to the shape, size, or weight of a particular
waste material. Since they are constructed of soil, they are rarely affected by the chemical
composition of a particular waste component or by any collective incompatibility of co-mingled
wastes. By comparison, composting and incineration require uniformity in the form and chemical
properties of the waste for efficient operation.
Out of all these methods, sanitary land filling is generally used for the waste disposal.
1.2. CONTAINMENT SYSTEM
The design of sanitary land filling typically involves some form of barrier that separates the
waste from the general ground water system. This barrier is intended to minimize the migration
of contaminants from the facility, thus the environmental impact of the facility is intimately
related to its design and long term performance. Natural clayey deposits or compacted clayey
liners frequently represent a key component of these barriers.
These days, barriers are usually includes one or more of the following types:
(i) Natural clayey soils such as lacustrine clay or clayey till;
(ii) Compacted clayey liners;
(iii) Cut-off walls;
(iv) Natural bedrock;
(v) Composite liner system consisting of geomembranes.
Out of the above mentioned types generally compacted clayey liners and composite liner system
with geomembranes are used on the waste disposal site.
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Compacted clay liners have been the subject of debate with respect to both the hydraulic
conductivity which can be achieved in the field and the potential impact of soil-leachate
interaction on hydraulic conductivity. However, the experienced has shown that with good
engineering practice and quality control, good quality, low hydraulic conductivity liners can be
constructed. Compacted clay liner can be designed with or without a leachate collection system.
The liner may be required for one or two reasons. Firstly, if the natural soil is fractured clayey
soil then the liner may be required to retard movements of contaminant along the fractures. The
second reason for constructing a clay liner is that, while intact, the surroundings natural soil does
not have a low enough hydraulic conductivity to provide an adequate barrier. There are some
situations where the conceptual designs may not provide sufficient confidence that there will be
negligible effect on ground water quality. Under these circumstances, an additional level of
engineering in the form of a secondary leachate collection system or hydraulic control layer may
be provided.
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Chapter-2
2.1. TYPES OF LINER
The different types of architecture used for landfill liners are as follows: single liner (clay or
geomembrane), single composite (with or without leak control), double liner, and double
composite liner.
2.1.1. Single Liner
A single liner system includes only one liner, which can be either a natural material (usually
clay), Figure 1a, or a single geomembrane, Figure 1b. This configuration is the simplest, but
there is no safety guarantee against the leakage, so a single liner may be used only under
completely safe hydro geological situations.
Figure 1. Cross section of different liner system
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A leachate collection system, termed as LCS (soil or geosynthetic drainage material), may be
placed above the liner to collect the leachate and thus decrease the risk of leakage.
2.1.2. Single Composite
A single composite liner system, Figure 1c, includes two or more different low-permeability
materials in direct contact with each other. Clayey soil with a geomembrane is the most widely
recommended liner.
Geotextile - Bentonite composites are often used as substitutes for mineral liners (liners using
stones or rocks as material) for application along slopes, even though many engineers prefer clay.
One of the main advantages of composite liners over single liners is the low amount of leakage
through the liner, even in the presence of damage, such as holes in the geomembrane.
2.1.3. Double Liner
A double liner system, Fig 1d, is composed of two liners, separated by a drainage layer called the
leakage detection system. A collection system may also be placed above the top liner. Double
liner systems may include either single or composite liners. Nowadays, regulations in several
states require double liner systems for MSW landfills. A clay layer may be placed under a double
liner made of membranes as shown in Figure 1e.
2.1.4. Double Composite Liner
Double composite liners are systems made of two composite liners, placed one above the other,
Fig 1f. They can include a LCS above the top liner and an LDS between the liners. Obviously,
the more components in the liner system, the more efficient is the system against leakage.
2.2. DESIGN CRITERIA FOR LAND FILL LINER
Solid waste land fill liners are design to prevent the movement of potentially harmful pollutants
beyond the boundaries of the landfill. The design criteria of a soil liners involves many facets
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such as selection of proper material, assessment of its chemical compatibility, analysis of slope
stability, consideration of the cracking due to desiccation of the material etc. Most of the
environmental agency requires a hydraulic conductivity value of less than 10-7
cm/sec for the
clay liners used to contain hazardous, industrial and municipal solid waste. Since the hydraulic
conductivity of a compacted soil depends upon its initial dry density and compaction water
content (Lambe, 1953), the field compaction conditions for a soil liner is generally taken into
account for verifying the proper compaction of the soil. In order to achieve this, the soil liner is
required to be compacted within a specified range of water content and a given dry density.
Figure 2. Acceptable water content and dry density for compacted soil
An acceptable zone which represents the combination of the zone of acceptable water content
and dry density is required for practice. The soil is generally required to be compacted at a
percentage P of the dry density and w of optimum moisture content. Previous research had
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shown that the value of P is usually 95% of dry density and w is 5% wet of optimum water
content.
There are four types of liner design-
2.2.1. Standard Design
In case of standard design we need minimum 4 ft. thick layer of re-compactedclay or other material with permeability of less than 10
-7cm/sec.
Finished liner must be sloped at 2%. This method is not suitable where large quantity of liner material is not easily
available on site or nearby site.
2.2.2. Alternative Design
This is the most desirable liner system because of the reduced permeability and thickness
requirement. It is feasible for areas with no available silt or clay material. The added cost
of synthetic liner is often out-weighted by cost reduction in clay material.
Alternative design provides a liner which consists of two liners. The thickness ofupper liner should be 50 mm and for lower liner 2 ft.
Upper liner should be made of synthetic material and lower liner of compactedclay. The hydraulic conductivity (k) of lower liner should be 10-6 cm/sec
The finish layer should be sloped at 2%2.2.3. Equivalent Design
Equivalent design is consist of some specific criteria like double liner and very deep natural
deposits of material with higher permeability than the standard case. It should be approved and
justify for the situation of the particular site.
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2.2.4. Arid Design
In that case liners are not required in arid areas like Rajasthan. In those places annual rainfall is
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operating life of landfill (i.e. construction purpose) and of liner after closer of the landfill. Soil
properties of nearby side are needed to be investigated. Hydrology and hydro-geology of the land
fill construction site is very helpful information for design of the landfill liner. Permeability and
different environment factor is very important for success of the landfill. Reliability of materials
such as seams and joint of geosynthetic membrane or material is very important. The following
items are some of the criteria that should be considered during the initial selection stage:
The selected site should be conformed to land use planning of the area. The selected site should have easy access to vehicles during the operation of the landfill. The site area should have adequate quantity of earth cover material that is easily handled
and compacted.
Landfill operation will not detrimentally impact surrounding environment. The selected site should be large enough to hold community waste for a reasonable length
of time.
2.4. TYPE OF LANDFILL LINER MATERIAL
Now a days several materials is being used for landfill liner material. Some of this is discussed
below;
2.4.1. Bentonite-Soil Liner
Bentonites and bentonite containing sealing materials are used for many years for sealing
purposes in foundation, dike construction, hydraulic engineering and landfill construction,
especially for encapsulation of old waste deposits. Because of their exceptional physical,
structural and chemical properties, bentonites are offering manifold possibilities to protect the
environment against the negative effects of dumping grounds. Often the observance of legal
regulations for waste dumping or for the encapsulation of contaminated areas is possible only by
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using bentonite containing sealing systems. Sodium Bentonite is easily available in powder form
that can be mixed with soil. Bentonite soil liner typically used in lifts 4 to 6 inches thick. For
Bentonite soil liner Plasticity Index (PI) should be greater than 15% and percentage finer should
be greater than 30%. For horizontal technical base liners the adsorption ability, the ion exchange
capacity and the swelling behavior of bentonite is important. For cut-off walls bentonite controls
the rheological behavior of the slurry and is responsible for the low permeability of the hardened
bentonite-cement-wall.
2.4.2. Asphalt Liner
The asphalt landfill liner has a number of advantages, the most important of which is increased
environmental safety. The asphalt liner can have a hydraulic conductivity that is 100 to 1,000
times lower than traditional compacted soil liners. Hydraulic conductivity describes how a liquid
flows through a material, and is important when preventing leakage from landfills. Landfills with
traditional soil liners may have a flow rate of about 140 gallons per acre per day. With asphalt
alone, the flow rate decreases to about nine gallons per acre per day. After completing the liner
with a layer of sprayed asphalt and a geosynthetic fabric on top, the flow is almost immeasurable.
Another environmental safety advantage of the asphalt liner is that it is more flexible and pliable
than traditional soil liners. This allows it to handle deformations without cracking, which
sometime happens with traditional soil liners. In addition, the layer of sprayed asphalt on the
liner's surface has the ability to seal itself against punctures, a feature traditional plastic
membranes do not possess. Asphalt liner is used as a mix which is known as Hydraulic Asphalt
concrete (HAC). HAC is a control hot mix of asphalt and a high quality mineral aggregate that is
compacted into a dense layer in order to achieve max permeability
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Asphalt landfill liners also take up less space. Traditional soil liners are more than two feet thick,
but asphalt liners are between four and six inches thick. Because the liner takes up less space, the
landfill can hold more trash. . Landfills that hold petroleum wastes, hydrocarbon wastes or
organic solvents could not use asphalt because these wastes could degrade the liner. He added
that installation costs are comparable between asphalt and traditional liners.
2.4.3. Soil Asphalt Liner
Asphalt is a dark brown to black cementious material, solid or semisolid in consistency, in which
the predominating constituents are bitumens (i.e., high molecular-weight hydrocarbons) that
occur in nature as such or are obtained as residual in the refining process (Yen, 1990).
Incorporation of affected soil as an ingredient to produce an asphaltic product is achieved by
stabilization, solidification and encapsulation. Stabilization is where chemical fixation
techniques render a waste less toxic or harmful to the environment. The hazard potential of what
was once considered a waste is subsequently reduced. Generally soil asphalt liner is mix of a
liquid asphalt and an aggregate of poorer quality than HAC. Typically the preferred soil type is
silty, generally soil with 10%-25% fines. In the areas of temperature variation asphalt liner is not
good.
2.4.4. Soil Cement Liner
Soil-cement linings are constructed with mixtures of sandy soil, cement and water, which harden
to a concrete-like material. The cement content should be from 2-8% of the soil by volume.
Permeability of mix can be achieved up to 10-6
cm/sec by compaction. However, larger cement
contents are used. For the construction of soil-cement linings two methods are in general use: (1)
the dry-mix method and (2) the plastic mix method. For erosion protection and additional
strength in large channels, the layer of soil-cement is sometimes covered with coarse soil. It is
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recommended the soil-cement lining should be protected from the weather for seven days by
spreading approximately 50mm of soil, straw or hessian bags over it and keeping the cover
moistened to allow proper curing. Water sprinkling should continue for 28 days following
installation. Soil-cement linings are often a viable alternative to channel lining if locally
available materials are not suitable for compressed earth or clay earthen lining. A great
advantage of this technique is that practically all types of soil normally encountered in earthen
channels can be used. For lining the beds of large channels this type of lining is considered ideal
from its combination of cost, efficiency and adequate results.
2.4.4.1. Dry-Mix Soil-Cement
The cement is distributed by hand-raking or by mechanical cement spreaders to a uniform depth.
While the cement is being mixed into the soil with a rotary tiller, water is added simultaneously
to the mixture from a tank truck or hose. After the cement and soil are thoroughly mixed and the
moisture content determined to be proper, the mixture is compacted by rubber-tyred road
compactors or heavily loaded trucks to approximately 100 mm thickness, within one hour of the
cement being spread. The soil mixture is usually cured for several days with intermittent
sprinkling. The durability and water tightness of the dry-mix soil-cement lining depends on the
soil used. Tests indicate that for ease of mixing, placement and using a low cement content, the
soil should be a well-graded, sandy, gravelly material. If it is poorly graded then the cement
content required is higher and cost increases. Material mixing for standard soil-cement is best
accomplished by travelling mixing machines or stationary plants. Mixing in place in the channel
and on side slopes has been found to be satisfactory.
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2.4.4.2. Plastic Soil-Cement Mix
Plastic soil-cement has higher water and cement content than dry-mix and a consistency
comparable to that of concrete used for slip-form lining. The soil is mixed with cement and water
in a paver or mixer traveling along the channel or in a stationary plant. The mix is then poured by
hand or by slip form on the sub-grade to produce the lining. Thickness ranges from 75-150 mm.
It is recommended that joints similar to those of concrete linings be provided. Installations of
soil-cement linings in the United States have shown that the greater the cement content of the
plastic mixture, the more durable the liner. All of the linings installed continue to be effective at
reducing both seepage and erosion. The sections with higher cement contents were made
serviceable for many years with reasonable maintenance.
2.5. NECESSITY FOR THE REQUIREMENT OF AN ALTERNATE LINERMATERIAL
The reviewed literature highlights that the liner is the most important element of a waste disposal
landfill that minimizes the migration of harmful contaminants to groundwater. Several
researchers have proposed different criteria for the design of different type of liners. In terms of
design there are two important factors: (1) thickness of the liner and (2) the mix design of soil
used in the liner. It is observed that the most significant factor affecting the performance of liner
is hydraulic conductivity and hence there is universally accepted guideline for minimum
hydraulic conductivity for liners. Hydraulic conductivity is found to depend on various factors
such as soil mix, water content, type of cement, dry density, degree of saturation, desiccation and
freezing. Some studies also report that hydraulic conductivity depends on the lift thickness, type
and weight of roller, number of passes and coverage and also the size of the clods. Several
empirical relationships and predictive correlations have been proposed for determining optimum
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water content, dry density and hydraulic conductivity of the soil based on easily measurable soil
properties.
In particular, hydraulic conductivity, compressibility and strength of the liners are crucial for
construction of the liners. However, no definite guidelines have been laid down for liner design
in terms of compressibility and strength. Also, no guideline exists to account chemical
interaction of liner-contaminant, which also plays a very important role in contaminant
migration. It is believed that this factor would help to reduce the thickness of the liners and
thereby make the project cost-effective.
There are different studies that deal with the use of variety of soil-admixture combinations for
liner construction. The details of all these studies and their result have been tabulated in Table 1.
From these studies it is found that one such material is fly ash which has a high utility potential
in these geo-environmental projects. Past and recent research has established the potential of fly
ash for use in a variety of construction applications. However, its utility in geo-environmental
projects still need to be explored in detail. To enhance its utility, the various criteria for liner
design need to be defined for fly ash type of materials. There are not many studies that deal with
the characterization of fly ash-cement mix that can be used for liners. Most of the studies deal
with strength and compressibility of the mix. The reviewed literature clearly suggest that a lot of
systematic studies are still required in terms of physical, chemical and geotechnical
characterization of fly ash-soil mix so that its mass utility can be enhanced in geo-environmental
projects like landfills.
The aim of this current research is it to evaluate the effective use of the mixtures fly ash and
cement as the liner material.
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Table 1. Past research and result
Sn Title Author Materials used
Hydrauli
conductivi
(cm/sec)
1 Feasibility of mudstone material as anatural landfill liner
Sheu et al.(1998) Mudstone material.
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Sn Title Author Materials used Hydraulicconductivity
(cm/sec)
10 Liners for waste containment
constructed with class F and C fly
ashes
Palmer et al. (1999) Class F and Class C fly
ash.
11 Stabilised fly ash use as lowpermeability barriers
Bowders et al. (1987) Class F fly ash, lime orcement
7.2x10-6
12 Permeability and leachate
characteristics of stabilized class F
fly ash.
Bowders et al. (1990) Class F fly ash,
bentonite, cement or
lime
Addition of
bentonite did
not affect k.
Permeation with 5%methanol with lime and
lime bentonite.
Decrease inhydraulic
conductivity.
Permeatition with 5%methanol.with cement
and cement bentonite
Increase in k.
Permeation with 3.2%
acetic acid solutionwith all specimen
except with 10%bentonite
Lowered thek.
13 Permeability and leaching
characteristics of fly ash liner
material.
Creek and Shackelford
(1992)
Class F fly ash, sand,
bentonite and cement.
1.2x10-4 to
4.5x10-7
14 Constant flow and constant
gradient permeability on sand-bentonite-fly ash mixtures.
Shakelford and Glade
(1992)
Sand bentonite fly ash
mixture
kupto
bentonitecontent up to
18% and
increasedlater.
15 Permeability of fly ash and alyash-sand mixtures
Vesperman et al.(1985)
Fly ash with sand (0 to90 %)
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Chapter-3
3.1. MATERIALS
In the first phase of this project was pure fly ash used. The specific gravity of the fly ash is 2.04.
To improve the hydraulic conductivity of the liner 43 grade Ordinary Portland cement with pure
fly ash was used. In order to study the effect of the cement content on the linear shrinkage,
hydraulic and compressibility behavior of the mixtures, tests were carried out for the five
different mixtures, i.e. 100 % fly ash, 98 % fly ash + 2 % cement, 95 % fly ash + 5 % cement,
93 % fly ash + 7 % cement and 90 % fly ash and 10 % cement. In order to get better idea,
mixture of fly ash and bentonite was also in the different proportions i.e. 95 % fly ash + 5 %
bentonite and 90 % fly ash + 10 % bentonite.
3.2. METHODS
3.2.1 Consolidation test
Consolidation test was carried out in order to assess the hydraulic conductivity and
compressibility of the mixture. Indirect determination of the hydraulic conductivity from
consolidation tests has several advantages and disadvantages over permeability tests, which are
in the following.
(i) can apply vertical pressures simulating those in field;
(ii) can measure vertical deformations;
(iii) can test sample under a range of vertical stresses;
(iv) can test compacted specimens and undisturbed samples;
(v) thin samples permits short testing time;
(vi) cost effective method for obtaining hydraulic conductivity data over a range sample states;
However it has also some disadvantages over other methods. Those are,
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(i) Some soil types may be difficult to trim into consolidation ring;
(ii) Thin samples may not be representative;
(iii) Potential for side wall leakage;
Despite of some disadvantages, the consolidometer permeability test is potentially the most
useful among the other methods viz. rigid wall permeameter and flexible wall (triaxial)
permeameter because of the flexibility which it offers for testing specimens under a range of
confining stresses and for accurate determination of the change in sample thickness as a result of
both seepage forces and chemical influence on the soil structure. Furthermore, the thinner
samples relative to the other test type means that the pore fluid replacement can be achieved in a
short time for a given hydraulic gradient.
The hydraulic conductivity can be calculated from the consolidation test results by fitting
Terzaghis theory of consolidation (Terzaghi, 1923) to the observed laboratory time-settlement
observation and extracting the hydraulic conductivity from calculated coefficient of
consolidation. The fitting operation was carried out using Taylors square root method. A
question may arise, how the hydraulic conductivity calculated by Terzaghis theory is
comparable to that determined directly by permeability tests. Terzaghi (1923) made such
comparison when he first developed the theory; he found satisfactory agreement. Casagrande and
Fadum (1944) reported that they always found satisfactory agreement provided that there was a
distinct change in curvature when the primary settlement curve merged with the secondary
settlement curve. Taylor (1942) presented comparison for remolded specimens of Boston blue
clay, based on the square root fitting method, and showed that the measured hydraulic
conductivity generally exceeded the calculated values. He attributed this difference in hydraulic
conductivity to Terzaghis assumption that the sole cause of delay in compression in the time
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required for the water to be squeezed out, i.e. to the hydraulic conductivity of the clay. Taylor
(1942) concluded that the structure of clay itself possessed a time dependent resistance to
compression so that the total resistance to volume change came partly from the structural
resistance of the clay itself. By attributing all of the resistance to low hydraulic conductivity,
Terzaghis theory must inevitably lead to an underestimate of the hydraulic conductivity. On the
based of several experiments Mesri and Olson (1971) concluded that the calculated hydraulic
conductivity was low only by 5 to 20 % for both remoulded and undisturbed clay provided the
clay is normally consolidated at the time of determination.
In regards to the determination of the hydraulic conductivity of clayey soil, the consolidation test
has been widely used (Newland and Alley, 1960; Mesri and Olson, 1971; Budhu, 1991;
Sivapullaiah et al., 2000). This test generally provides the hydraulic conductivity comparable
with the permeability test (Terzaghi, 1923; Casagrande and Fadum, 1944) although slightly
underestimates the hydraulic conductivity compared with the permeability test (Taylor, 1942;
Mitchell and Madson, 1987). Consolidation tests were carried out to determine the hydraulic
conductivity of the mixtures.
The test was carried out on the sample of 60 mm diameter and 20 mm thickness according to
ASTM D 2435 using standard consolidometers. The samples were prepared by adding water to
the different fly ash - cement mixtures (with cement content of 0 %, 2 %, 5 %, 7 %, and 10 %),
and fly ash-bentonite mixtures (with bentonite content of 5 % and 10 %). Then the mixtures were
mixed with water to obtain the optimum moisture content (OMC). Then the sample was kept in a
humidity controlled desiccator for 24 hours in order to attain the moisture equilibrium. The
inside of the ring was smeared with a very thin layer of silicon grease in order to avoid friction
between the ring and soil sample. Filter paper was placed at the bottom and top of the sample. A
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top cap with a porous stone was placed above the soil sample. Then the mixtures were
compacted in the consolidation ring to its maximum dry density (MDD). The entire assembly
was placed in the consolidation cell and positioned in the loading frame. The consolidation ring
was immersed in the water. Then the consolidation cells were allowed to equilibrate for 24 hours
prior to commencing the test. All the samples were initially loaded with a stress of 0.5 kg/cm2,
increasing by an increment ratio of 1 (i.e. 0.1, 0.2, 0.5, 1, 2 kg/cm2
etc) to a maximum pressure
of 8 kg/cm2.
3.2.2. Linear Shrinkage test
Linear shrinkage, as used in this test method, refers to the change in linear dimensions that has
occurred in test specimens after they have been subjected to soaking heat for a period of 24 hours
and then cooled to room temperature.
Most insulating materials will begin to shrink at some definite temperature. Usually the amount
of shrinkage increases as the temperature of exposure becomes higher. Eventually a temperature
will be reached at which the shrinkage becomes excessive. With excessive shrinkage, the
insulating material has definitely exceeded its useful temperature limit. When an insulating
material is applied to a hot surface, the shrinkage will be greatest on the hot face. The differential
shrinkage which results between the hotter and the cooler surfaces often introduces strains and
may cause the insulation to warp. High shrinkage may cause excessive wrap age and thereby
may induce cracking, both of which are undesirable.
The test was carried out on the sample of 25 mm diameter and 125 mm thickness according to
using standard mould confirming to IS 12979: 1990. Soil sample weighing about 150 g from the
thoroughly mixed portion of the material passing 425 micron IS Sieve [IS 460 (Part 1): 1985]
obtained in accordance with IS 2720 (Part 1): 1983 was taken for the test specimen.
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About 150 g of the soil sample passing 425 micron IS Sieve was placed on the flat glass plate
and thoroughly mixed with distilled water, using the palette knives, until the mass becomes a
smooth homogeneous paste, with moisture content approximately 2 % above the liquid limit of
the soil. In the case of clayey soils, the soil paste shall be left to stand for a sufficient time (24
hours) to allow the moisture to permeate throughout the soil mass. The thoroughly mixed soil-
water paste was placed in the mould such that was slightly proud of the sides of the mould. The
mould was then gently jarred to remove any air pockets in the paste. Then the soil was leveled
off along the top of the mould with the palette knife. The mould was placed in such way that the
soil-water mixture (paste) can air dry slowly, until the soil was shrunk away from the walls of the
mould. Drying was completed first at a temperature of 60 to 65 C until shrinkage has largely
ceased and then at 105 to 110 C to complete the drying. Then the mould and soil was cooled
and the mean length of soil bar measured because the specimen was become curved during
drying.
3.3. DETERMINATION OF HYDRAULIC CONDUCTIVITY AND COMPRESSIBILITY
For each pressure increment the change in the thickness of soil sample was measured from the
readings of the dial gauge. Then the change in the void ratio corresponding to an increase in the
overburden pressure was calculated by the Eq. 1,
e= H(1+e)/H (Eq. 1)
Where, H = Change in the thickness of sample due to increase in pressure
H = Initial thickness of the sample, e = Initial void ratio
From the calculated void ratios, a plot of void ratio, e vs log of pressure, p, was plotted. The
compression index (Cc) was calculated from the slope of this curve, or
Compression index (Cc) = - ji
ji
pp
ee
/log
(Eq. 2)
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Where,
ei = Void ratio corresponds to a consolidation pressure ofpi
ej = Void ratio corresponds to a consolidation pressure ofpj
From the consolidation test result, a time-settlement curve was obtained at each pressure
increment. The coefficient of consolidation cvwas obtained using Taylors square root time (T)
method.
The co-efficient of volume change can be calculated by the formula,
mv= av /(1+e) (Eq. 3)
where, av = coefficient of compressibility
= /e where,
= Change in pressure
e = Change in void ratio
The hydraulic conductivity, k, was calculated using the Eq. 4 for various pressure increments
using the cv
, and coefficient of volume change, mv
k= cvm
v
w(Eq. 4)
where, w
is the unit weight of the pore fluid
3.3.1. DETERMINATION OF LINEAR SHRINKAGE
The linear shrinkage of the soil shall be calculated as a percentage of the original length of the
specimen from the following formula:
Linear Shrinkage (LS), (%)= (1 - Ls/ L) 100%
Where,
L = Length of the mould (mm)
Ls = Length of the of the oven dry specimen (mm)
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Chapter-4
RESULTS AND DISCUSSION
4.1. General
The results of different tests carried out on various fly ash-cement mixes and fly ash-bentonite
mixes are presented in this chapter.
4.1.1 Compaction properties of the various fly ash-cement mixtures
Compaction test is carried out for the five different fly ash-cement mixtures, i.e. pure fly ash,
98 % fly ash + 2 % cement, 95 % fly ash + 5 % cement, 93 % fly ash + 7 % cement, 90 % fly ash
+ 10 % cement. The optimum moisture content (OMC) and maximum dry density (MDD) for all
the five mixtures has been tabulated in Table 2. The data in the table shows that the OMC and
MDD for the mixtures increase with the increase in the cement content of the mixtures.
Table 2. OMC and MDD values of fly ash cement mix with different proportion
Mixing Combination Optimum Moisture Content
(OMC), %
Maximum Dry Density
(MDD)
kg/m3
Pure fly ash 17.0 131998 % fly ash + 2 % cement 18.2 1339
95 % fly ash + 5 % cement 19.3 1339
93 % fly ash + 7 % cement 19.9 1368
90 % fly ash + 10 % cement 20.4 1377
4.1.1.1. Hydraulic conductivity
Hydraulic conductivity is one of the most important criteria for soil to be used as a liner material
at the waste disposal site. Most of the regulatory authority in the world has recommended that
the material to be used as a liner material must have a minimum value of hydraulic conductivity
of 10-6 cm/sec compacted at MDD and OMC. Result of the hydraulic conductivity for all the five
mixtures shows that all mixtures satisfy the hydraulic conductivity criteria required for a landfill
liner. Result shows that the hydraulic conductivity value for the five mixtures decreased with a
decrease in the void ratio. The decreases in the hydraulic conductivity with the decrease in the
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void ratio was quite steep at the beginning, however, with a further decrease in the void ratio
there was a marginal decrease in the hydraulic conductivity.
In a comparison among the five mixtures, it can be seen that with the increase in the cement
content the hydraulic conductivity decreases. In other words, at the same void ratio mixture withhigher cement content exhibits a lower hydraulic conductivity. When the cement content
increases and it comes in contact with the water, it holds the fly ash particles on its surface and
gets solidify and in turn blocks the flow path thereby reducing the hydraulic conductivity.
Figure 3. Relation between void ratio and hydraulic conductivity for the five mixtures
1.E-08
1.E-07
1.E-06
1.E-05
0.44 0.46 0.48 0.5 0.52 0.54 0.56 0.58
Void ratio
Hydrauliccond
uctivity(cm/sec
100% fly ash
98% fly ash + 2% cement
95% fly ash + 5% cement
93% fly ash + 7% cement
90% fly ash + 10% cement
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4.1.1.2. Compressibility
Figure 4 shows the relation between the pressure and void ratio for the five mixtures. The result
shows that with an increase in the overburden pressure the void ratio of the mixture decreases.
The increase in the overburden pressure on the five mixtures can be correlated with the increase
in the pressure on the liner due to the increase in the weight of the overburden weight due to
dumping of more and more waste material. The result shows that the decrease in the void ratio
with an increase in the pressure is quite marginal in the beginning. However, with an increase in
the load the mixtures get compressed significantly. Result shows that the mixture with a higher
fly ash content possessed a lower void ratio at any given overburden pressure. This can be
attributed to the presence of the higher amount of fine particles in the fly ash. With the increase
in the fine content of the mixture the void ratio decreases.
Figure 4. Relation between void ratio and over burden pressure for the five mixtures
0.42
0.44
0.46
0.48
0.5
0.52
0.54
0.56
0.58
0.01 0.1 1 10Pressure (kg/cm
2)
Voidratio
100% fly ash
98% fly ash + 2% cement
95% fly ash + 5% cement
93% fly ash + 7% cement
90% fly ash + 10% cement
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Compression index (Cc) and expansion index (EI) for all the five mixtures was determined from
the Fig. 4 and tabulated in Table 3. The data in Table 3 shows the compression index of the
mixture gets affected marginally by the presence of the cement. However, the expansion index
gets affected significantly due to cement content. The expansion index decreases with an
increase in the cement content. The increase in the cement makes the mixture more cementitious
and it gets hardened due to the increase in the over burden pressure. With the removal of the over
burden pressure it re-bounced less significantly in comparison to the pure fly ash.
From the values of expansion index we can say that for all five type of mix the potentiality of
expansion is very low because all three values are in between 0-20.
SL.
NO.
Mixing Composition Compression Index
(Cc)
Expansion Index (EI)
1 Pure fly ash 0.077138 9.4
2 98 % fly ash + 2 % cement 0.077032 6.33 95 % fly ash + 5 % cement 0.095965 2.5
4 93 % fly ash + 7 % cement 0.025885 1.9
5 90 % fly ash + 10 % cement 0.081374 1.5
Expansion Index (EI) Potential Expansion
0-20 Very Low21-50 Low
51-90 Medium
91-130 High
>130 Very High
Table 3. Values of com ression index and ex ansion index of fl ash-cement mix
Table 4. Classification of Potential Ex ansion of Soils Usin EI
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4.1.1.3. Linear Shrinkage
Liner shrinkage for all the five type of fly ash-cement mixtures was found to be zero. The length
and the diameter of all the five mixtures did not reduce after keeping in oven for 24 hours.
4.1.4. Co-efficient of consolidation(cv)
The coefficient of consolidation (cv) signifies the rate at which a saturated soil sample undergoes
one dimensional consolidation when subjected to an increase in the vertical consolidation
pressure. A large value ofcv indicates a faster rate of consolidation whereas a low value indicates
a slower rate of consolidation. Figure 5 shows the plot between co-efficient of consolidation (cv)
against the vertical consolidation pressure for the five mixtures. The result for the five mixtures
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
0.04
0.045
0.01 0.1 1 10pressure (kg/cm
2)
Co-efficientofcompressibility,mv(cm2/kg)
100% fly ash
98% fly ash + 2% cement
95% fly ash + 5% cement93% fly ash + 7% cement
90% fly ash + 10% cement
Figure 5. Relation between co-efficient of compressibility and over burden pressure forthe five mixtures
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shows that cv decreases with the increase in the over burden pressure. Result also shows that the
value ofcv differs significantly initially, however, with the increase in the pressure the difference
in the value ofcv for the five mixtures decreases significantly.
Figure 6. Relation between coefficient of consolidation and over burden pressure for the
five mixtures
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0.1
0.01 0.1 1 10
Pressure (kg/cm2)
Co-efficientofconsolidation(cm2/sec)
100% fly ash
98% fly ash + 2% cement
95% fly ash + 5% cement
93% fly ash + 7% cement
90% fly ash + 10% cement
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4.2.1. Compaction properties of the mixtures
Compaction test was carried out for the three different fly ash and bentonite mixtures, i.e. pure
fly ash, 95 % fly ash + 5 % bentonite, and 90 % fly ash + 10 % bentonite. The optimum moisture
content (OMC) and maximum dry density (MDD) for all the three mixtures has been tabulated in
Table 5. The data in the table shows that the OMC and MDD for the mixtures increase with the
increase in the bentonite content of the mixtures.
Table 5. OMC and MDD values of fly ash- bentonite mix with different proportion
Mixing Combination Optimum Moisture Content
(OMC)
Maximum Dry Density
(MDD) kg/m3
Pure Fly ash 17.0 % 1319
95% Fly ash + 5% Bentonite 18.0 % 1398
90% Fly ash + 10% Bentonite 19.8 % 1412
4.2.2. Hydraulic conductivity
In case of fly ash and bentonite mix result of hydraulic conductivity shows that all three mixtures
satisfy the hydraulic conductivity criteria require for a liner material. For all the mixtures the
value of hydraulic conductivity was found to be less than 10 -6 cm/sec, the limiting criteria for the
use of a landfill liner material. From Fig. 7 shows that the hydraulic conductivity value for the
three mixtures decreased with a decrease in the void ratio. The decrease in the hydraulic
conductivity with the decrease in the void ratio was quite steep at the beginning for the pure fly
ash and 95 % fly ash + 5 % bentonite mixtures. However, the hydraulic conductivity of the 90 %
fly ash + 10 % bentonite decreased uniformly with the decrease in the void ratio.
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In a comparison among the three mixtures, it can be seen that with the increase in the bentonite
content the hydraulic conductivity increases. In other words, at the same void ratio mixture with
higher bentonite content exhibits a higher hydraulic conductivity. Generally, the hydraulic
conductivity tends to decreases with the increase in the bentonite content (Chapuis, 1990). This
opposite trend can be explained in terms of the presence of various salts in the fly ash (Ohtsubo
et al., 2004). When fly ash-bentonite mixtures comes in contact with water, the various cations
such as Na+, Ca2+ leached out from fly ash and react with the bentonite present in the mixture.
Because of these cations the repulsive force of the bentonite decreases and the bentonite becomes
flocculated (van Olphen, 1977). As the bentonite gets flocculated, the flow path becomes open
and the hydraulic conductivity increases (Benson and Daniel, 1990).
1.E-08
1.E-07
1.E-06
1.E-05
0.39 0.41 0.43 0.45 0.47 0.49 0.51 0.53 0.55 0.57
Void ratio
Hydraulicconductivity(cm
/sec
90% Fly ash + 10% Bentonite
95% Fly ash + 5% Bentonite
100 % Fly ash
Figure 7. Relation between void ratio and hydraulic conductivity for the three mixtures
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4.2.3. Compressibility
Figure 8 shows the relation between the pressure and void ratio for the three mixtures. The result
shows that with an increase in the overburden pressure the void ratio of the mixture decreases.
From the figure we can say that lower bentonite content gives higher void ratio with the increase
overburden pressure. The result shows that the decrease in the void ratio with an increase in the
pressure is quite marginal in the beginning. However, with an increase in the load the mixtures
get compressed significantly.
0.3
0.35
0.4
0.45
0.5
0.55
0.6
0.1 1 10
Pressure (kg/cm2)
Voidratio
90% Fly ash + 10 % Bentonite
95% Fly ash + 5% Bentonite
100% Fly ash
Figure 8. Relation between void ratio and over burden pressure for the three mixtures
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Figure 9. Relation between pressure and co-efficient of compressibility
Compression index (Cc) and expansion index (EI) for all the two mixtures was determined from
the Fig. 7 and tabulated in table 6. The data in table 6 shows the compression index of the
mixture gets affected by the presence of the bentonite. The increase in the bentonite results in
increase in compression index (Cc). However, the expansion index gets affected marginally due
to bentonite content. From the values of expansion index we can say that for all three type of mix
the potentiality of expansion is very low because all three values are in between 0-20. The
0
0.01
0.02
0.03
0.04
0.05
0.06
0.1 1 10
Pressure (kg/cm2)
Co-efficientofcompressibility,mv(cm2/kg)
90% Fly ash + 10 % Bentonite
95% Fly ash + 5% Bentonite
100% Fly ash
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expansion index increases with an increase in the bentonite content. This behavior of the mixture
is due to the excessive swelling potentiality of bentonite and With the removal of the over burden
pressure it re-bounced very significantly in comparison to the pure fly ash. The data in table 6
also shows that linear shrinkage of fly ash and bentonite mixture increases with the increase in
the bentonite content. This is due to the swelling potentiality of bentonite because after drying
swelling of the mixture decreases, eventually to zero. As a result the mixture shrunk.
Table 6. Values of compression index, expansion index and linear shrinkage of fly ash and
bentonite mix
Sl. No. Mixing Composition Compression Index
(Cc)
Expansion
Index(EI)
Linear
Shrinkage %1 Pure Fly Ash 0.077139 9.4 0
2 95 % Fly ash + 5 %
Bentonite
0.114449 11.4 1.6
3 90 % Fly ash + 10 %
Bentonite
0.332663 17.7 3.2
4.2.4. Co-efficient of consolidation(cv)
In case of fly ash and bentonite mix the values of Co-efficient of consolidation is very large atthe beginning. Figure 10 shows the plot between co-efficient of consolidation (cv) against the
vertical consolidation pressure for the three mixtures. The result for the three mixtures shows
that cv decreases with the increase in the over burden pressure. Result also shows that the value
ofcv differs significantly initially.
4.3. Comparisons between cement and bentonite mix with fly ash (5% and 10%)
4.3.1. Optimum moisture content and maximum dry density
All the values of optimum moisture content and maximum dry density are tabulated below. From
Table 7 it is clear that bentonite mix gives higher value of optimum moisture content and
maximum dry density for both the 5 % and 10 % mixtures.
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Figure 10. Relation between coefficient of consolidation and over burden pressure for the fly ashand bentonite mixtures
4.3.2. Hydraulic conductivity
It is recommended that the material to be used as a liner material must have a minimum value of
hydraulic conductivity of 10-6 cm/sec compacted at MDD and OMC. In Fig.10 a graphical
relation between void ratio and hydraulic conductivity for 5 % and 10 % cement and bentonite
content has been established. Result shows that hydraulic conductivity value for the four
mixtures decreased with a decrease in the void ratio. The figure shows that 95% fly ash and 5%
cement mixture gives lower value of hydraulic conductivity.
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.1 1 10
Pressure (kg/cm2)
Co-efficiento
fconsolidation,cv(cm
2/sec)
90% Fly ash + 10 % Bentonite
95% Fly ash + 5% Bentonite
100% Fly ash
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Table 7. values of OMC and MDD 5 % and 10 % cement and bentonite respectively
Sl. No. Mixing CombinationOptimum Moisture
Content (OMC)
Maximum Dry Density
(MDD) kg/m3
1 95% fly ash + 5% cement 19.3 % 1339
2 95% fly ash + 5% bentonite 18.0 % 13983 90% fly ash + 10% cement 20.4 % 1368
4 90% fly ash + 10% bentonite 19.8 % 1412
1.E-07
1.E-06
1.E-05
0.35 0.4 0.45 0.5 0.55 0.6
Void ratio
HydraulicConductivity(cm/sec
95% fly ash + 5% cement
95% fly ash + 5% bentonite
90% fly ash +10% bentonite
90% fly ash + 10% cement
Figure 10. Relation between void ratio and hydraulic conductivity for 5 % and 10 % cement and
bentonite content
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4.3.3. Compressibility
Figure 11 shows the relation between pressure and void ratio for the four mixtures. The result
shows that the both 5 % and 10 % cement content gives higher value than 5 % and 10 %
bentonite content. Whereas 90 % fly ash and 10 % bentonite gives lowest value of void ratio.
The increase in the overburden pressure on the four mixtures can be correlated with the increase
in the pressure on the liner due to the increase in the weight of the overburden pressure because
of more waste material.
In Fig.12 A relationship between pressure and co-efficient of compressibility for 5 % and 10 %
cement and bentonite content has been plotted. From the figure it is clear that the characteristic
of both 5 % and 10 % bentonite is parabolic. Whereas in case of cement the values of co-
efficient of compressibility are higher at the beginning then it decreases with the increase in
overburden pressure.
0.35
0.4
0.45
0.5
0.55
0.6
0.01 0.1 1 10
Pressure (kg/cm2)
Voidratio
95% fly ash + 5% bentonite
95% fly ash + 5% cement
90% fly ash + 10% bentonite
90% fly ash + 10% cement
Figure 11. Relation between pressure and void ratio for 5% and 10% cement and bentonite content
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0
0.01
0.02
0.03
0.04
0.05
0.06
0.01 0.1 1 10Pressure (kg/cm
2)
Co-e
fficientofcompressibility
95% fly ash + 5% bentonite
95% fly ash + 5% cement
90% fly ash + 10% bentonite
90% fly ash + 10% cement
Figure12. Relation between pressure and co-efficient of compressibility for 5% and 10%cement and bentonite content
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4.3.4. Co-efficient of consolidation(cv)
Figure13 shows the plot between pressure and co-efficient of consolidation for 5 % and 10 %
cement and bentonite content. Result shows that for 5 % and 10 % bentonite content co-efficient
of consolidation decreases greatly at the beginning and after 0.5 kg/cm2
pressure it maintains
almost a linear stability. In case of 5 % and 10 % cement content compression index of the
mixture gets affected marginally by the presence of the cement. Result also shows that the value
ofcv differs significantly initially, however, with the increase in the pressure the difference in the
value ofcv for the four mixtures decreases significantly.
0.01
0.06
0.11
0.16
0.21
0.26
0.31
0.36
0.01 0.1 1 10Pressure (kg/cm
2)
Co-efficientofcons
olidation(cm2/sec)
95% fly ash + 5% bentonite
95% fly ash + 5% cement
90% fly ash + 10% bentonite
90% fly ash + 10% cement
Figure13. Relation between pressure and co-efficient of consolidation for 5% and 10%
cement and bentonite content
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5. CONCLUSIONS
From the series of experimental data it is clear that fly ash has a bigger role in the application of
geo-environmental engineering especially in landfill liner design. The data from compaction test
shows that both optimum moisture content and maximum dry density increases with increase in
the use of bentonite and cement with fly ash. With further laboratory testing likely consolidation
test reveals that hydraulic conductivity for both fly ash-cement and fly ash-bentonite is less than
10-6 cm/sec. It also shows that co-efficient of consolidation and co-efficient of compressibility
both decreases with the increase in the overburden pressure. But on the other hand from linear
shrinkage data it is clear that fly ash-cement mixture is not showing any sign of shrink because
of cement hardening. In case of fly ash-bentonite mix it shows considerable amount of shrink
which increases with the increase in bentonite content. From the pressure-void ratio curve it can
be concluded that with the increase in the fine content of the mixture results in the decrease in
the void ratio. So at the end it can be concluded that 95 % fly ash + 5 % cement and 95 % fly ash
+ 5 % bentonite is suitable to use in landfill liner.
.
6. SCOPE FOR THE FUTURE WORK
Based on the result presented above, further studies can be carried out:
I. To determine the shear strength of different proportion of fly ash + cement and fly ash +bentonite mixture.
II. Determination of compaction, strength, compressibility and permeability characteristicsof alternative material.
III. To develop a new setup for locally available soil.
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IV. To evaluate the suitable fly ash-expansive soil mix that can be used as landfill liner.V. To propose different combination of parameters as design criteria for fly ash-expansive
soil mix.
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