Seminar report

ABSTRACT

A geosynthetic clay liner (GCL) is a woven fabric-like material, primarily used for the lining

of landfills. It is a kind of geomembrane and geosynthetic, which incorporates a bentonite or

other clay, which has a very low hydraulic conductivity. The resulting lower permeability

slows the rate of seepage out of the landfill. Due to environmental laws, any seepage from

landfills must be collected and properly disposed of, otherwise contamination of the

surrounding ground water could cause major environmental and/or ecological problems. The

lower the hydraulic conductivity the more effective the GCL will be at retaining seepage

inside of the landfill. Bentonite composed predominantly (>70%) of montmorillonite or other

expansive clays, are preferred and most commonly used in GCLs. A general GCL

construction would consist of two layers of geosynthetics stitched together enclosing a layer

of processed sodium bentonite. Typically, woven and/or non-woven textile geosynthetics are

used, however polyethylene or geomembrane layers or geogrid geotextiles materials have

also been incorporated into the design or in place of a textile layer to increase strength.

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1. INTRODUCTIONGeosynthetic clay liners (GCLs) represent a relatively new technology that is currently

gaining acceptance as a barrier system in municipal solid waste landfill applications. GCL

technology offers some unique advantages over conventional bottom liners and covers. For

eg.GCLs are very fast and easy to install, have low hydraulic conductivity and have the

ability to self repair any rips or holes caused by the swelling properties of the bentonite from

which they are made. GCLs are low permeable materials increasingly considered for

deployment as hydraulic barriers in mining facilities and other industrial facilities. GCLs are

manufactured hydraulic barriers consisting of bentonite clay bonded to a layer, or layers, of

geosynthetic material. Bentonite is a high swelling clay that has a very low hydraulic

conductivity when hydrated with water. The primary purpose of the carrier geosynthetics is

to hold and support the bentonite such that it can be installed in a uniformly thin layer

without the loss of bentonite or changes in thickness. Unrienforced GCLs are held together

by chemical adhesives, whereas reinforced GCLs are needle-punched or stitch-bonded to

increase the shear strength of the product.

2. GEOSYNTHETIC CLAY LINERS

Geosynthetic clay liners commonly known as GCLs are woven fabric like material, primarily

used for lining of landfills. It consist of two layers of woven or non woven geosynthetics

with an intermediate layer of bentonite composite, which has very low hydraulic

conductivity.These two layers are known as carrier and cover geotextile.The bentonite can be

in the form of granular or powder. Commonly the thickness of GCL varies from 5 mm to 10

mm. They stick together together to form a composite by adhesives, needle punching, stitch

bonding or combination of them.

Geosynthetic clay liners are covered with soil after installation to protect them from stress

concentrations due to construction activities and permanent structural loads. Geosynthetic

materials can increase the characteristics of clay. The bentonite clay can be of sodium

bentonite and calcium bentonite. GCL products are produced by several large companies in

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North America, Europe, Asia. Bentonite has thick double layers and high swelling

capacity.Its lower permeability slows the seepage of covering systems.

Fig.1 Geosynthetic Clay Liners

2.1 FORMS OF GCL

Geotextile encased is the sandwich of geotextile-clay-geotextile

Adhesive bonded :- mixture of clay and adhesive to hold sandwich together

Eg :- Claymax 200R,Claymax 600CL

Stitch-bonded :- held together with parallel rows of stitches

Eg :- Claymax 500SP

Needle-punch :- held together with fibres punched through,sometimes bonded

to geotextile

Eg :- Bentomat,Bentofix

Geomembrane-supported is the sandwich of clay and geomembrane

Held together by adhesive mixed into clay

Eg :- Gundseal

Bentonite swelling seals GCLs

Self-seal at overlaps and for some other types extra bentonite is applied to overlap

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GCLs need to be covered quickly to prevent rapid hydration,uneven swelling and

self-sealing

Fig.2 Bentofix and Bentomat

Fig.3 Claymax 200R

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Fig.4 Claymax 500SP

Fig.5 Gundseal

2.2 OTHER NAMES OF GCLs

Clay blanket

Bentonite blanket

Bentonite mats

Prefabricated Bentonite clay blanket

Clay Geosynthetic Barriers

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3. NEEDLE-PUNCHED GCL

Needle punching is a nonwoven process by which the fibres are mechanically entangled to

produce a nonwoven fabric by repeated penetration of barbed needles through a performed

dry fibrous web. The needle board is mounted on a beam which is given an up and down

reciprocating motion by means of an eccentric crank mechanism. As a result, the fibres are

mechanically interlocked, thereby providing the mechanical strength.

Needle-punched GCLs are the commonly used type. The performance of needle-punched

GCL depends upon the durability and security of the outer layers. In this the clay core acts as

barrier component.

Fig.6 Needle-punched GCL

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4. INSTALLATION OF GCL

Operators can install GCL products much faster and easily than CCLs. Manufactureres

usually specify individual GCL installation procedures.

4.1 SURFACE AND SUBGRADE PREPARATION

The subgrade or fill material should be free of any angular or sharp rocks larger than 2 inches

(5 cm) in diameter as well as any organics or other deleterious materials. Compaction of the

subgrade should be in accordance with the design specifications, or, at a minimum, to the

extent that no rutting is caused by installation equipment or vehicles.

Prior to deployment of the BENTOMAT geosynthetic clay liner, the subgrade should be final

graded to fill all major voids or cracks and proof rolled to provide a smooth surface for the

installation of the liner. The surfaces to be lined should be smooth and free of debris, roots

and angular or sharp rocks larger than 1 inch (2.5 cm) in diameter.Minor variations in the

subgrade surface are tolerable; however, no sharp irregularities should exist. Installation over

other geosynthetic materials requires no additional surface preparation.

4.2 BENTOMAT HANDLING AND PLACEMENT

Depending on the type of subgrade at the site, the typical equipment used for deployment

may range from an extendible boom forklift to a front end loader or backhoe. Suspending the

BENTOMAT roll using a spreader bar and a core pipe through the core will facilitate

deployment and will prevent damage to the panel edges caused by the suspending chains or

straps.

Methods of deployment will vary based on site-specific conditions such as slope angle, berm

widths, the type of project, the type of subgrade surface, and the subgrade preparation. As a

general guideline, all seams should run parallel to the direction of the slope. Flat areas

require no particular orientation; however, attention should be paid to the overlap orientation

to prevent seam displacement during cover placement.

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Fig.7 extendable boom forklift

Deployment should proceed from the highest elevation to the lowest to facilitate drainage in

the event of precipitation. BENTOMAT may be deployed by pulling the material from a

suspended roll, or by weighing down one end of the roll end and then allowing it to unroll as

the installation equipment slowly moves backwards along the intended path of deployment.

4.3 SEAMING PROCEDURE

BENTOMAT seams are formed with a Volclay sodium bentonite enhanced overlap.

BENTOMAT has been engineered so that when properly installed and hydrated, a small

amount of internal sodium bentonite will extrude through the edges where overlaps exist;

however, secondary seaming measures are also recommended to insure that a continuous seal

is achieved between panels. A minimum of a 6-inch to 9-inch overlap should exist at all seam

locations. A lap line as well as a match line has been printed on the BENTOMAT panel

edges at 6 and 9 inches respectively, to ensure the proper overlap is achieved. The

BENTOMAT panels should be adjusted to smooth out any wrinkles or creases between

adjacent panels, leaving a proper seam where the overlapping panel covers the lapline of the

underlying panel but leaves the matchline exposed.

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Fig.8 GCL Overlap

4.4 ANCHORING PROCEDURE

Anchor trenches may be excavated in a number of ways, depending upon the size of the

project and the maneuvering area available at the top of the slope. The preferred methods are

to use a ditch trencher (set to the specified depth) or a small backhoe equipped with a bucket

of appropriate width. Bentomat should be placed in the trench such that the end of the panel

covers the entire trench floor but does not extend up the rear wall.The size of the anchor

trench depends on site-specific criteria such as the soil type and general condition, the angle

and length of the slope, as well as the thickness and type of proposed cover materials. In any

case, anchor trench backfill should be well compacted to prevent water intrusion or pending

and to prevent liner pullout. When using BENTOMAT in conjunction with other

geosynthetic materials, the BENTOMAT may be put in a separate trench or placed as

otherwise specified by the engineer.

4.5 PENETRATION SEALING

For sealing around penetrations, a small notch should be made around the circumference of

the pipe, into the subgrade. Volclay bentonite should then be packed around the pipe in the

notch and on adjacent areas so that the pipe is encased by a pure bentonite seal. The

BENTOMAT panel should then be placed over the penetration and slit into a "pie"

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configuration where the pipe is to protrude. This procedure will create a snug fit between the

BENTOMAT and the pipe once the laps are trimmed.

More sodium bentonite should then be spread around the cut edges of the BENTOMAT

against the pipe and over adjacent areas.

To complete the detail, a collar of BENTOMAT should be cut in a manner similar to that

made on the main panel and fit around the pipe, with additional Volclay sodium bentonite

applied into any gaps that may remain.

When Bentomat is used above or in conjunction with other geosynthetic materials, notching

below the liner may not be possible. In these cases, sprayable bituminous coatings may be

applied around the penetrations and any other critical areas. All other penetration sealing

steps should be followed to ensure a watertight seal is produced.

4.6 STRUCTURE SEALING

Another critical area in an installation is the attachment or sealing of BENTOMAT to

foundation walls, drainage outlets or concrete structures. Sealing panel edges against a wall

or foundation is accomplished with the use of pure Volclay bentonite.

To start, a small notch should be made against the edge of the object to be sealed. The notch

should be packed full of Volclay bentonite. The BENTOMAT panel is then brought up to the

structure and trimmed to fit against the wall of the structure as shown. Care must taken to

ensure that the Bentomat is kept directly against the structure as the cover material is applied.

Once hydrated, the Volclay bentonite seal will allow for settlement or other stresses that may

tend to pull the BENTOMAT from the edge.

4.7 PROTECTIVE COVER

The protective cover should be composed of well graded soils, sands or crushed gravel free

of sharp edged stones larger than 1 inch (2.5 cm) in diameter. Cover should be spread by low

ground pressure equipment.

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A minimum cover thickness of 12 inches should be kept between heavy equipment and the

liner at all times. No vehicles should drive on the BENTOMAT until proper cover has been

placed to the specified depth.Once proper depth of cover soils have been applied, compaction

equipment may be used.Care should be taken to push materials upslope wherever possible

and to avoid pinching or shifting the liner by making sharp turns or sudden stops.

4.8 ACTIVATION

For fresh water applications, the water to be contained will activate the BENTOMAT. If

highly contaminated or non-aqueous liquids are to be contained, however, the BENTOMAT

must be prehydrated with fresh water for 48 hours prior to use. Approximately one-quarter

gallon of fresh water per square foot is necessary for prehydration. Prehydration may be

accomplished by flooding the impoundment, using a sprinkler system, or by natural rainfall.

In landfill applications, the leachate is typically sufficient to hydrate the BENTOMAT.

Fig.9 GCL Role

Fig.10 GCL role fixed on spreader bar

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Fig.11 spreading of GCL

4.9 MAINTENANCE

Rips or tears may be repaired by completely exposing the affected area, removing all foreign

objects or soil, and by then placing a patch over the damage, with a minimum overlap of 12

inches on all edges.

Accessory bentonite should be placed between the patch and the repaired material at a rate of

a quarter pound per lineal foot of edge spread in a six-inch width.

If damage occurs on a slope, the same basic procedure should be used; however, the edges of

the patch should be fastened to the repaired liner with contact cement, epoxy, or some other

construction adhesive, in addition to the bentonite-enhanced seam.

Fig.12 Placing of GCL

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5. PERFORMANCE FACTORS

The key performance factors of GCLs are:

5.1 HYDRAULIC CONDUCTIVITY

Hydraulic conductivity is one of the most important criteria for soil to be used as a liner.With

the addition of GCL in the mixture the hydraulic conductivity is found to be reduced

significantly.

5.2 BEARING CAPACITY

An adequate layer of cover soil (according to the product manufacturers’ recommendations),

placed on GCLs during installation, prevents a decrease in liner thickness with the

application of a load. Without a sufficient soil layer, GCLs become compressed, raising their

hydraulic conductivity (i.e., making them more permeable) and reducing their effectiveness

as a barrier. Needle-punched GCLs are less susceptible to lateral bentonite displacement

under concentrated loads than adhesive bonded and stitch bonded.

5.3 LONG TERM RELIABILITY

The geotextile or geomembrane in GCL products remains durable for long periods of time.

5.4 SHEAR STRENGTH

Depending on the particular configuration of the barrier system, GCL technology can provide

considerable shear strength (i.e., the maximum stress a material can withstand without losing

structural integrity). In particular, a geotextile-backed GCL, with bentonite affixed via stitch

bonding, provides additional internal resistance to shear in the clay layer.

Needle-punching yields an even stronger, more rigid barrier. In addition, needle-punching

requires the use of a nonwoven geotextile on at least one side. These GCL configurations

provide enhanced interface friction resistance to the adjoining layer, an important

consideration for landfill slopes.

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5.5 SLOPE STABILITY

Comparison of the forces needed to maintain stability (eg.friction ) with the forces driving

instability (eg:soil weight) uses a Factor of Safety (FS), which is defined as the ratio of

available strength to shear stress at equilibrium.

FS > 1 means, the slaope is stable.

FS < 1 means that it is potentially unstable, and a sliding failure is possible.

5.6 FREEZE AND THAW CYCLES

Freeze and thaw cycles do not affect GCLs used in landfill bottom liner applications because

these systems are installed below the frost line. hydraulic conductivity of GCLs is not

affected by freeze and thaw cycles.

5.7 GAS PERMEABILITY AND DIFFUSION

Gas permeability and the gas diffusion coefficient decreased with increasing GCL

gravimetric water content and apparent degree of saturation. Gas permeability remains

constant and high up to 100% gravimetric water content (45% apparent degree of saturation)

and gas diffusion coefficient remains constant up to 50% gravimetric water content (20%

apparent degree of saturation) respectively.

6. ADVANTAGES AND DISADVANTAGES

6.1 ADVANTAGES

Prevention of Root Penetration

Increasing Resistance against Desiccation

Lower Permeability

Barrier against Ion Exchange

Rapid installation/less skilled labour/low cost

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Very low hydraulic conductivity to water if properly installed

It can withstand large differential settlement

Excellent self healing characteristics

Not dependent on availability of local soils

Field hydraulic conductivity test not required

Easy to repair

Reduce overburden stress on compressible substratum

6.2 DISADVANTAGES

Loss of bentonite during placement especially for powder bentonite.

Thin layer of GCL cause possibility to be punctured during or after installation.

Slightly increase in hydraulic conductivity before self repair can result in escaping

leachate from the barrier.

7. RESEARCH AND RESULTS

The American Society for Testing and Materials (ASTM) has developed standardized

laboratory tests.

7.1 STANDARD TEST METHOD FOR THE MEASUREMENT OF HYDRAULIC

CONDUCTIVITY

This test method covers laboratory measurement of hydraulic conductivity (also referred to

as coefficient of permeability) of GCL with a flexible wall permeameter. Test values for

hydraulic conductivity depend on the degree of effective overburden stress around the GCL

during testing. In laboratory hydraulic conductivities of geotextile-supported GCLs vary

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approximately between 10 -12 and 10-10 m/s. Hydraulic conductivity decreases as confining

stress increases.

Fig.12

7.2 STANDARD TEST METHOD FOR MEASURING MASS PER UNIT OF GCLs

The mass per unit area is determined by weighing (oven-dried) specimens of known initial

size after drying it in an oven over a sufficient time period to remove the moisture from the

GCL.

The mass per unit area of the clay component of the GCL can be estimated by subtracting the

manufacturers reported nominal mass per unit area of the synthetic component(s) from the

total GCL mass per unit area. Test result of mass per unit area of GCL is 3.66 kg/m2 .

7.3 STANDARD TEST METHOD FOR MEASURING SELF HEALING CAPACITY

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Self healing capacity of both GM-GCLs and GT-GCLs has been investigated by laboratory

leakage rate tests.

The factores affecting test results are,

7.3.1 Overburden stress

Hydrated bentonite is squeezed into a damage hole to increase the self healing capacity. For

stress upto 200kPa, the self healing capacity increase with an increase in the value of stress.

7.3.2 Size of damage hole

A damage hole up to 30 mm diameter can be self healed.

7.4 STANDARD TEST METHOD FOR DETERMINATION OF WATER

(MOISTURE) CONTENT OF SOIL BY THE MICROWAVE OVEN METHOD

At first a moist GCL specimen is placed in a suitable container and its mass is determined.

Then it is placed in a microwave oven and subjected to an interval of drying. After that it is

taken out from the oven and its new mass is determined. This procedure is repeated until the

mass becomes nearly constant. ASTM gives the test result as 12%.

8. APPLICATIONS OF GCL

Geosynthetic clay liners are used for numerous applications around the world.

8.1 WASTE

GCLs are ideal for lining waste containment areas, such as landfills, that need the strongest

protection possible to avoid leakage and groundwater contamination.

8.1.1 Solid Waste Landfill

GCLs landfill lining system provide significantly lower permeability, improved ease of

installation and increased amount of usable space

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Fig.13 Solid Waste Landfill

8.1.2 Hazardous Waste Landfills

If hazardous waste is not properly contained, it could result in lives being endangered. GCLs

offer low permeability, chemical resistance and U.V. protection for highly reliable

containment.

Fig.14 Hazardous Waste Landfill

8.2 WATER

Water conservation is more important than ever. From canals to manmade reservoirs like

those on golf courses, GCLs provide affordable, effective protection against leakage and

damage

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Fig.15 Application on water tailing pond

8.3 MINING

During mining process GCLs prevent the leakage of toxic gases and also provide high

durability.

Fig.16 GCLs in mining

8.4 ENERGY

In response to increased demand for energy due to population growth and settlement of urban

areas, many companies are looking for ways to boost production at existing power plants and

explore new energy resource. GCLs provide solutions to many applications for energy

customers such as shale gas and brine, evaporation, and cooling ponds.

Fig.17 GCL in energy management

8.5 CIVIL

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Geosynthetics play a pivotal role in civil engineering projects such as transportation and

retention walls. GCLs help to built roadways, control storm water, waterproof green roofs

and acts as vapour barriers.

Fig.18 Civil works

8.6 AGRICULTURE AND AQUACULTURE

GCLs are trusted by aquaculture facilities to contain water and control its quality and by

animal farms to decrease contamination.

Fig.19 GCL in agriculture

8.7 INDUSTRIAL

GCL geomembranes, concrete protection and drainage products deliver sound control of on-

site water storage, treatment reservoirs and secondary containment.

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Fig.20 Industrial lining

9. COSTS OF GCL

Cost of installation mainly ranges from $0.05 to $0.10 per meter square.

Factors of affecting the cost of GCLs are:

Shipping distance : as shipping distance increases cost also increases

Size of job : incase of risky jobs cost of installation also increases

Market demand : as all products if market demand increases, cost of installation also

increases

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10. CONCLUSION

There is no doubt that geosynthetic clay liners have gained widespread popularity over the

past decade as a substitute for compacted clay liners in cover systems. As an augmentation to

compacted clay liners in bottom liners of landfills, environmental protection barriers in

transportation facilities or storage tanks, and as single liners for canals, ponds or surface

impoundments. The lower the hydraulic conductivity the more effective the GCL will be at

retaining seepage inside of the landfill. Due to the flexibility of production and rapid

innovation, the performance of different types of GCLs may vary significantly.

GCL which has lower hydraulic conductivity, if installed properly can withstand large

differential settlement and also it has excellent self healing capacity. It does not depend on

the availability of local soils. They are easy to repair and also it reduce overburden stress on

compressible substratum. Field hydraulic conductivity test is not required for GCLs. Its

installations are also safer and long lasting. They can achieve ever-better ecological,

economical and performance-related benefits for engineers.

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REFERENCES

[1] Rouhollah Soltani Goharrizi, Fazlollah Soltani and Bahador Abolpour, 2013, “Study of

Geosynthetic Clay Liner Layers Effect on Decreasing Soil Pollution in the Bed of Sanitary

Land Fills,” published in International Journal of Water Resources and Environmental

Engineering, DOI: 10.5897/IJWREE2013.0421, Vol 5(8), August

[2] Mochamad Arief Budihardjo, Amin Chegenizadeh and Hamid Nikraz, 2012,

“Geosynthetic Clay Liner as Landfill’s Leachate Barrier,”published in International

Conference on Civil and Architectural applications (ICCAA), December

[3] Jian Yu1, Jigang Shi1 and Han Liu2, 2012, “Case Study on Application of Geosynthetic

Clay Liner in Canal Lining in Hetao Irrigation Area,” Inner Mongolia, ICID 21st

International Congress on Irrigation and Drainage,15-23 October

[4] P. Phillips and M. Eberle , The use of Geosynthetic Clay Liners (GCL's) in containment

applications, International journal Geofabrics Australasia Pty Ltd, Australia.

[5] Y.Liua,1 , A. Bouazzab,* , W.P.Gatesb,2 , R.K. Rowec,3 , 2015, “Hydraulic Perfomance of

Geosynthetic Clay Liners,” Geotextile and Geomembranes

[6] Bouazza, A. and Bowders, J. (2009). “GCLs in Waste Containment Applications,” Taylor

Francis, U.K. (in press).

[7] Rouf, M.A , Bouazza, A, Singh, R.M , Gates, W.P , Rowe, R.K, 2015, “Gas Diffusion

Coefficient and Gas Permeability of an Unsaturated Geosynthetic Clay Liner,” published in

Geosynthetics Conference 2015, February

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