PRODUCED BY GIGSA : Geosynthetic Clay Liners · Geosynthetic Clay Liners Developed over 20 years...

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Established in 1983 and Dedicated to the Scientific and Engineering Development of Geosynthetics and Associated Technologies A newsletter of the Geosynthetics Interest Group of South Africa in Association with the South African Institution of Civil Engineering PRODUCED BY GIGSA : www.gigsa.org The South African Chapter of the International Geosynthetics Society PAGE 1 NOVEMBER 2009 EDITION Environmental Protection incl. Waste Containment As can be seen the areas where GCL’s are used are wide and varied. As with all geosynthetic products, they will only perform according to expectations if they are properly designed for their intended application. Application Function Typical Confining Pressure Landfill Capping To inhibit the ingress of liquids and the uncontrolled 10 — 50 kN/m 2 escape of gases Landfill Lining Typically in combination with a geomembrane to 50 to 1000 kN/m 2 prevent the uncontrolled leakage of leachate and gasses. Canals, Rivers and In areas where the water level is constant they can Less than 50 kN/m 2 Surface Impoundments be used as the single barrier, in most cases Hydraulic gradient i of over 100 replacing a compacted natural clay liner Environmental To stop hazardous liquids from transport vehicles Less than 50 kN/m 2 Protection entering sensitive locations, mainly in the infrastructural environment such as roads, railways & airports Applications [email protected] Geosynthetic Clay Liners Developed over 20 years ago, Geosynthetic Clay liners (GCLs) according to ISO definition (also called geosynthetic barrier-clay (GBR-C) bentonite liners or bentonite mats) are defined as a manufactured hydraulic barrier consisting of bentonite clay bonded to a layer or layers of geosynthetic materials. The main purpose of a GCL is to reduce the flow of liquid through a barrier system. They work by utilising the properties of sodium bentonite, which swells when hydrated with water and forms an impermeable gel-like structure. In landfill applications GCLs are commonly used in combination with HDPE geomembranes in the base and in capping systems. However in caps, GCLs are also used as the sole barrier. In both cases the GCL replaces a compacted clay liner thereby saving airspace (in landfills), and the system is able to reduce the overall construction costs. Reinforced GCLs are the most common type and the reinforcement of the majority of GCLs is by needlepunching. Design Considerations In recent years some concern has been raised regarding an issue known as ion exchange. This occurs when a sodium cation of the clay is preferentially exchanged with a cation of an electrolyte such as calcium, potassium or magnesium. When this occurs, the swelling of the bentonite is reduced and the hydraulic conductivity of the bentonite is increased. It has been found that polyvalent cations such as calcium or magnesium are the most problematic in this regard. Whilst an issue, this ion exchange can be mitigated if the entire system around the GCL is designed properly to begin with. It is known that by using a high enough overburden stress, an increase in the confining stress of the GCL occurs which decreases the hydraulic

Transcript of PRODUCED BY GIGSA : Geosynthetic Clay Liners · Geosynthetic Clay Liners Developed over 20 years...

Page 1: PRODUCED BY GIGSA : Geosynthetic Clay Liners · Geosynthetic Clay Liners Developed over 20 years ago, Geosynthetic Clay liners (GCLs) according to ISO definition (also called geosynthetic

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Established in 1983 and Dedicated to the Scientific and EngineeringDevelopment of Geosynthetics and Associated Technologies

A newsletter of the Geosynthetics InterestGroup of South Africa in Association with theSouth African Institution of Civil Engineering

PRODUCED BY GIGSA : www.gigsa.org

The South African Chapter ofthe InternationalGeosynthetics Society

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As can be seen the areas where GCL’s are used are wide and varied. As with all geosynthetic products, they will only performaccording to expectations if they are properly designed for their intended application.

Application Function Typical Confining PressureLandfill Capping To inhibit the ingress of liquids and the uncontrolled 10 — 50 kN/m2

escape of gasesLandfill Lining Typically in combination with a geomembrane to 50 to 1000 kN/m2

prevent the uncontrolled leakage of leachate and gasses.Canals, Rivers and In areas where the water level is constant they can Less than 50 kN/m2

Surface Impoundments be used as the single barrier, in most cases Hydraulic gradient i of over 100replacing a compacted natural clay liner

Environmental To stop hazardous liquids from transport vehicles Less than 50 kN/m2

Protection entering sensitive locations, mainly in theinfrastructural environment such as roads, railways & airports

Applications

[email protected]

GeosyntheticClay Liners

Developed over 20 years ago, Geosynthetic Clay liners(GCLs) according to ISO definition (also calledgeosynthetic barrier-clay (GBR-C) bentonite liners orbentonite mats) are defined as a manufactured hydraulicbarrier consisting of bentonite clay bonded to a layer orlayers of geosynthetic materials. The main purpose ofa GCL is to reduce the flow of liquid through a barriersystem. They work by utilising the properties of sodiumbentonite, which swells when hydrated with water andforms an impermeable gel-like structure. In landfillapplications GCLs are commonly used in combinationwith HDPE geomembranes in the base and in capping

systems. However in caps, GCLs are also used as thesole barrier. In both cases the GCL replaces a compactedclay liner thereby saving airspace (in landfills), and thesystem is able to reduce the overall construction costs.

Reinforced GCLs are the most common type and thereinforcement of the majority of GCLs is byneedlepunching.

Design Considerations

In recent years some concern has been raised regardingan issue known as ion exchange. This occurs when asodium cation of the clay is preferentially exchangedwith a cation of an electrolyte such as calcium, potassiumor magnesium. When this occurs, the swelling of thebentonite is reduced and the hydraulic conductivity ofthe bentonite is increased. It has been found that polyvalentcations such as calcium or magnesium are the mostproblematic in this regard.

Whilst an issue, this ion exchange can be mitigated ifthe entire system around the GCL is designed properlyto begin with. It is known that by using a high enoughoverburden stress, an increase in the confining stressof the GCL occurs which decreases the hydraulic

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conductivity. This could help mitigate the effects of ionexchange. However the conditions are in relation to eachother so that it is not possible to give specific values.For low confining stress applications such as waterimpoundments, an investigation should be done on thecover soil that is going to be used, and an increase incover soil depth is valuable to improve the long-termperformance of the GCL.

In any case if there is any doubt then the free swell test(ASTM D5890) and the fluid loss test (ASTM D5891)are a very nice compatibility test to investigate whetherthere is a possibility of an effect on the bentonite. Havinga chemical analysis as well as the pH value and electricalconductivity of the site leachate also helps experiencedengineers to indicate if an influence on the long-termpermeability value could occur. Hydraulic conductivitytests allow a longer term investigation.

For applications where the GCL is going to be placed ona slope, the internal shear strength of the GCL is veryimportant. Bentonite alone or unreinforced GCLs havean internal residual friction angle when hydrated of approx4-5 degrees. Needlepunched reinforced GCLs showsignificantly better performance, having a higher peakshear strength. It has been suggested by the GRI that aminimum peel value of 360N/m tested according toASTM D6768 should be accepted. Various Bentofix¤publications show a correlation between the PeelStrength of needlepunched GCLs and the internal shearvalue. However, it is recommended that these are verifiedto site-specific conditions in direct shear tests.

Bentofix NSP recently being installed at Lufhereng Attenuation Ponds,Soweto.

Research study

To summarise the efficiency and long-term performanceof Bentofix¤ GCLs, NAUE carried out long-term in-situtests and came to the following conclusions after thefirst 10 years of the study. Some conclusions andconsequences for landfill engineering can be drawn fromthese investigations of cover systems with GCLs installedin lysimeters and exposed to mid-European climateconditions (Editor s note: mid European climatic conditionsvary significantly from South African climatic conditions,and indeed, our climate varies considerably within SouthAfrica itself. Please use your discretion in the applicationof this information):

Large scale testing in lysimeters under in-situconditions is an effective and economic way to provethe long-term permeation behaviour of cover systemswith GCLs.

High-quality-GCLs, filled with 4,500 to 5,500g/m2 of high premium grade powder sodium bentonitecovered by soil layers of more than one meter in thicknessand exposed to humid climate conditions show a veryhigh sealing efficiency. During ten years of investigation,only 0.5 to 1.4 % of the rainfall permeated through theGCLs.

A replacement of silty cover soil with a waterpermeability of 10-7 m/s by sand with a water permeabilityof about 10-3 m/s leads to a decrease of permeation,due to a steadier water supply and therefore lessdesiccation of the GCL during the summer periods.

The sealing efficiency of the GCL depends onthe amount of drainage water supplying the bentonitewith water. After a temporary increase of permeationdue to lower water content, GCLs regained full sealingefficiency in the following winter period. This may becalled reversible material behaviour or self-healingcapacity.

GCL sealing systems with a thin cover and asmall overburden load show a decrease in sealingefficiency after some years. Lower overburden andtherefore small confining pressures against swellingpressure obviously leads to an increase in permeabilityand to a reduced self-healing capacity.

For landfill engineering, the positive effects ofsufficient and steady drainage water supply above GCLson their sealing capacity must be taken into considerationwhen drainage layers on GCL liners have to be designed.The thickness of the overburden on caps is dependenton climate conditions and the type of cover soil, andshould be selected in such a way as to create a steadywet local climate in the soil pores above the GCL.

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PAGE 3

Prez SezPrez Sez

Geosynthetic Greetings,

Garth JamesPresident

[email protected]

South Africa is not likely to see such a gathering of worldgeosynthetics experts in a hurry again although 2013 ismooted to be the year for the next IGS African RegionalConference.

At this suggestion, by the IGS Council, we were quick toselfishly propose our North African neighbours, like Algeria,so that we would be free from organizing another colossalevent, certainly not on my watch! Maybe the young andenergetic members of GIGSA have other ideas!

In my previous Prez Sez I was at pains to avoid too muchdoom and gloom about the prospects for the civil engineeringindustry looking ahead yet I was encouraged to see thecomments made at an economic workshop recently held inJohannesburg hosted by Consulting Engineers South Africa(CESA) at which three leading experts in their fields gave theiropinions on the Impact of the Global Economic Crisis on theConsulting Engineering Industry.

In his welcoming address Felix Fongoqa, President of CESA,stated that the workshop was important in order for consultantsto look at strategies for a sustainable future for business inSouth Africa and the African continent. He posed the questionas to whether the economy was heading for a cliff or justgoing to experience slight turbulence. He also referred to theplanned Government spend of nearly R 800 billion oninfrastructure development over the next three years.

One of the experts, Iraj Abedian, CEO of Pan African Investmentand Research Services and Chairperson of Bigen Africa,pointed out that over the past 14 years the ratio of theconstruction sector as a contributor to GDP has been risingand therefore the relative growth in this sector of the economyhas been above average. He pointed out that — not only wasconstruction booming in South Africa — but also China, Dubaiand Sydney. And, in fact, worldwide leading to a shortage ofskills and capacity issues.

He said that Government will channel a great deal of resourcesto improve urban infrastructure. South Africa s constructionindustry is unlikely to be hit as hard as some other countries.

He concluded with Times are tough but opportunities havenot dried up and cost consciousness is bound to rise rapidly .

(Business Report, Tuesday, September 29, 2009)

There is hope after all!

Sadness and relief are some of the emotions that were feltpost-GeoAfrica 2009.

Sadness, because a very successful conference that broughttogether old and new friends from the internationalgeosynthetics community, has been and gone.

Relief, because all that hard work, anxiety, excitement, sleeplessnights, preparation has passed and one can breathe again.However one is left to pick up the pieces, so to speak, ofone s former life with family, jobs, friends and hobbies.Restful weekends are now a reality again.

There is indeed life after GeoAfrica!

Unfortunately the work load had not marked time in anticipationof our return to the office it had marched on greeting us witha plethora of tasks to do in as little time as possible.

I would like to convey my heartiest congratulations and thanksto Peter Legg and his Organizing Committee for the supremeeffort that made GeoAfrica such a success. Peter Daviesdeserves much credit for his efforts in putting together a greattechnical programme.

My sincere thanks go to Lesley Ferreira and her CebisaConference staff for an extremely well co-ordinated conference.I was most proud to be President of GIGSA witnessing theculmination of many months of sheer hard graft on the partof our GIGSA committee and members.

We used this unique opportunity of international exposure tomake our GIGSA Awards to include the President s Award,Development in Technology Award, Construction Award andHonorary Life Membership Awards.

The final report from Lesley confirmed that the conferencewas a resounding success and the evaluation forms collectedfrom the delegates were all complimentary. The remarks aboutcertain operational issues at the conference were highlightedand we were well aware of some of these shortcomings duringthe conference.

We are very grateful to our key note speakers, special speakers,presenters, sponsors, exhibitors and delegates for theircontribution toward a wonderful conference.

One big disappointment to the Organizing Committee was therelatively poor turn out from our local consulting fraternity.This was through no lack of trying on the part of GIGSA andI can safely say that those who did not attend have missedout on a unique opportunity which turned out to be the gainof 40 of their colleagues. I understand that most of thosepeople reason that geosynthetics do not play a huge part intheir daily design work and they tend to refer such specialitywork to those more in the know.

However Geosynthetics are established engineering expedientsworldwide and cannot be ignored by our engineers. Thosewho have chosen to keep pace with the developments ingeosynthetics have certainly gained the advantage.

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Note from theEditor

Welcome to our new GIGSAmembers

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0��������&�����(�������������*&(�������/������'�����������/�������.0�1�����������������.

Shakira SattarGIGSA Newsletter Editor

Send your comments andsuggestions for the GIGSAnewsletter to the Editor at:[email protected]

Individual Members:Peter Dimaio (Anchor Lining Systems)

Honorary Life Members:Clifford Gundle Rod DraytonDu Toit Viljoen Peter DaviesRonnie Scheurenberg Falk Hedrich

GIGSA Membership Fees 2010

We are pleased to inform youthat there will be no increase inthe membership fees for 2010.

Student Members:Jacobus PretoriusAnnemarie De LangeTshepo SathekgeNhlanhla TshabalalaChris BerryPhathamandla SitholePhetile NkosiMpho ShikwambanaTsanwani MalumaThabo GopaneLucky MolefeAwelani RamadwaNkosinathi DubeKagiso LetlalaMosa TsoaiDavid MphafudiGiancarlo WingraveSamuel DitseleKarabo KgapholeQuinton BothaTshidiso SelemelaMoretsi SeratleloDuma SenzoKatlego PicoThabani MolaloseFannie Nkuna

New members will get a special mention in each edition of the GIGSA newsletterso watch this space!

Tasneem VawdaKenneth MoyaKeoagile KerilengYoosuf EssopjeeJabulani MakafaneBrenden JordaanBernita KalanMelamy MoiponeTal BugaiAdelle van StadenThulani NgwawbaWerner van den BergJoanne MullerJoanne MullerCorne ElsWessel SwartKayakazi MafutaAbdul MagimbiCalvin LangleyWhitney PailmanMandla DyodoShaym NathaSameer SulimanByron HendrickseDillon SwanepoelReynier van Rooyen

This page is dedicatedin memory of

Alan Lever(14 September 1924 - 8 July 2009)

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GIGSA AWARDS 2009Photo Gallery

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The GIGSA awardees were nominated by themembers of GIGSA and after adjudication of thesubmissions by the Awards Committee the awardswere presented at the GeoAfrica 2009 conferencein Cape Town.The GIGSA 2009 awards are as follows:

GIGSA President’s Award 2009

The Kelly Nicole Legge Floating Trophy awarded to:Peter LeggIn honour of his excellence and dedication to GIGSAin his capacity as Immediate Past President of GIGSA,Conference Chairman for GeoAfrica 2009 and IGSCouncil Member

The GIGSA Development in Technology Award

Awarded to:Moore Spence and Jones (Malcolm Jaros)Bombela Civils JV (Pty) LtdKaytech Engineered FabricsFor the Multiple Layered Geosynthetic ReinforcedEmbankment over Sinkhole Area, Snake Valley,Gauteng Rapid Rail Link

The GIGSA Construction Award

Awarded to:AquatanFor the Buzwagi Gold Mine Water Harvesting andFloating Cover Reservoir, TanzaniaCommendation — GIGSA Construction AwardAwarded to:Dept. of Water Affairs (Engineering Services)Iliso Consulting EngineersKaytech Engineered FabricsUsutu River Emergency Works, RSA-MozambiqueBorder

Honorary Life Membership Awards

Clifford GundleRod DraytonDu Toit ViljoenPeter DaviesRonnie ScheurenbergFalk HedrichFor outstanding service to GIGSA and the geosyntheticindustry in South Africa.

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Report

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PAGE 7

GeoAfrica 2009Photo Gallery

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PAGE 8

LiquidGeosyntheticsThe Way of the Future?By: Dr. Kevin GastGast Press Office

The uncontrolled penetration or leaking of water intoor through building structures, undergroundexcavations, dam walls, foundations and mine tunnelsis one of the most difficult, dangerous and costlyproblems faced by engineers, owners and operators.A company dedicated to finding solutions for thesetypes of problems is GAST which has been workingin this industry for over 40 years. The development ofthe Sovereign product was primarily focused on findinga solution for water ingress where accessibility isrestricted or denied. Typical examples of these wouldbe water retaining concrete structures such as dams,reservoirs or retainer walls. Another application wouldbe water ingress in geological formations as oftenencountered in mining activity. Water has the uncannyability of making an appearance in the most unwantedplaces.

The Gast Sovereign system can be implementedwherever leakages occur where the source point isunknown or not easily identifiable. The system is uniqueand rather simplistic in application in that reverse waterpressure is applied so as to determine the hydrostaticindex of the leak, water is then reverse pumped throughthe leak containing a par ticular isotope or marker.

An investigation then takes place to determine if theleak is an accomplice to other related water problemsor not.

The same water is then used as a carrier so as toenable liquidated rubber to be pumped in until thiscorresponds with the isotope marker and the existinghydrostatic head. Once this is achieved the entireplug is then activated by a unique catalyst, bringingabout homogenization and solidification of all the rubberpar ticles held in suspension. Once this has beenachieved, the more hydrostatic pressure increases themore firmly the plug is forced against the apertures.This then creates a mechanical seal with a successratio of up to 80% on first injection. The plug itselfremains flexible, is non-toxic and non-hazardous.Success has also been achieved on suspendedconcrete structures such as parking decks, roof decksand other construction areas post initial construction.Founded in 1961 GAST has expanded into variousdifferent industries such as civil engineering,commodities brokerage, construction and development.

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Hydraulicconductivity

m/sec ASTMD5887

Max 5E-11 1.6E-08(cap, G:L+)

5.1E-11

GCL 2 from the cappingsystem, mid reach up

embankment.

Hydraulicconductivity

at 35kPa

m/sec ASTMD5887

Max 5E-11 1.6E-08(cap, G:L+)

1.6E-09

Free swell ml ASTMD5890

Min 24 7.0

Atterberg liquidlimit

ASTMD4318

105

Index flux at70kPa

(m3/m2)/s ASTMD5887

Max 1E-08 3.5E-09

Hydraulicconductivity at

70kPa

m/sec ASTMD5887

Max 5E-11 1.6E-08(cap, G:L+)

1.7E-11

Index flux at35kPa

(m3/m2)/s ASTMD5887

Max 1E-08 3.9E-09

Sample Units TestMethod

GRI-GCL3Specifications Min Requ.1

GCL 1 from thecapping system, top

of embankment.

Property Results for GCLsamples

Hydraulicconductivity

at 35kPa

m/sec ASTMD5887

Max 5E-11 1.6E-08(cap, G:L+)

1.7E-11

Performance ofGCL in LandfillAppl icationsCase StudyBy:R.C.Emery. Jeffares & Green (Pty) LtdB. Makgekgenene. Jeffares & Green (Pty) Ltd

INTRODUCTIONThis article is an extract from a paper presented at theGeoAfrica Conference in 2009. It documents a studythat was undertaken to examine the medium-to-longterm performance of˚a particular GCL˚in a landfill basinlining system and in a landfill cap system installed atBellville South Landfill Site, Cape Town. The studydetermined cer tain parameters in exhumed GCLsamples.Samples were taken from Cells 1 and 4 at Bellville

South Landfill site and from the capping face on thewestern side of the landfill. Cell 1 has a compositeprimary lining system using HDPE and GCL and wasinstalled approximately six years ago. Cell 4 has acomposite primary lining system using HDPE and GCLand was installed approximately three years ago. TheGCL and soil cap on the western embankment wasinstalled approximately six years ago. The sampleswere removed by hand and were tested in commercialand institutional laboratories. The results are presentedtogether with the method of sampling and the methodof testing.The research does not consider the chemistry of theresults or the reasons for any change in character ofthe GCL. The primary objective of the research wasto determine, at an engineering level, whether therehas been a change in the primary function of the GCLat Bellville South Landfill, this being the permeabilityand swell-ability irrespective of ion exchange.

The information presented here is from a case studydone on a specific GCL installed in a par ticularenvironment and application from a specific positionat one site and thus does not necessarily reflect theperformance of GCLs in general.

TEST RESULTSTable 1 below lists the geotechnical test results fromthe four selected GCL samples.

PAGE 9

Table 1: Summary of results and comparisons thereof

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PAGE 10

1. Minimum Requirements for Waste Disposal By Landfill

The GCL samples for the capping and basal linings systemswere at least six years old when tested.

Hydraulicconductivityat 140kPa

m/sec ASTMD5887

Max 5E-11 1E-08(liner, G:L+)

5.3E-12

Hydraulicconductivity at

70kPa

m/sec ASTMD5887

Max 5E-11 1E-08(liner, G:L+)

9.5E-12

GCL 4 from the basallining system in

Cell 4.

Hydraulicconductivity

at 35kPa

m/sec ASTMD5887

Max 5E-11 1E-08(liner, G:L+)

1.6E-11

Free swell ml ASTMD5890

Min 24 13.5

Atterberg liquid limit ASTMD4318

177

Index flux at 140kPa (m3/m2)/s ASTMD5887

Max 1E-08 1.0E-09

Index flux at 70kPa (m3/m2)/s ASTMD5887

Max 1E-08 2.4E-09

Index flux at 35kPa (m3/m2)/s ASTMD5887

Max 1E-08 4.1E-09

Hydraulicconductivityat 140kPa

m/sec ASTMD5887

Max 5E-11 1E-08(liner, G:L+)

6.2E-12

Hydraulicconductivity

at 70kPa

m/sec ASTMD5887

Max 5E-11 1E-08(liner, G:L+)

1.1E-11

GCL 3 from the basallining system in

Cell 1.

Hydraulicconductivity

at 35kPa

m/sec ASTMD5887

Max 5E-11 1E-08(liner, G:L+)

2.0E-11

Free swell ml ASTMD5890

Min 24 6.0

Atterberg liquid limit ASTMD4318

108

Index flux at 70kPa (m3/m2)/s ASTMD5887

Max 1E-08 9.6E-09

Index flux at 35kPa (m3/m2)/s ASTMD5887

Max 1E-08 4.1E-08

at 70kPa

Sample Units TestMethod

GRI-GCL3Specifications Min Requ.1Property Results for GCL

samples

Free swell ml ASTMD5890

Min 24 13.0

Atterberg liquid limit ASTMD4318

227

Index flux at 140kPa (m3/m2)/s ASTMD5887

Max 1E-08 1.4E-09

Index flux at 70kPa (m3/m2)/s ASTMD5887

Max 1E-08 2.4E-09

Index flux at 35kPa (m3/m2)/s ASTMD5887

Max 1E-08 3.8E-09

continued...Performance of GCL in Landfill Applications

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The conference will be organized by both IGS Brasil(the Brazilian chapter of IGS) and ABMS (BrazilianSoil Mechanics Association), and supported by ABINT(Brazilian Non-Textile and Technical Fabric Industry

Association), under the sponsorship of IGS(International Geosynthetics Society).

Go to www.9icg-brazil2010.info

The GCL taken from the capping system, as describedabove, appear to still have sufficient hydraulic integrityto serve as a barrier for such an application, comparedto the Minimum Requirements of the Department ofWater Affairs and Forestry (1998.)

The GCL taken from the top of the embankment appearsto have maintained its original installed state of hydraulicintegrity whilst the GCL sampled from mid-reach (of theembankment) has reduced.

Most manufactured GCLs today achieve a maximumhydraulic conductivity of 1E-11 m/s. This said, the GCLsamples taken from the basal lining system and the topof the embankment still maintain this conductivity, whilstthe GCL sample taken from mid-reach of the embankmenthas dropped below the as-manufactured conductivity.

The free swell index for all GCL samples taken from thecap has reduced significantly, yet not in relation to itshydraulic performance. This could be due to chemicalchange in the bentonite.

The GCL taken from basal lining system also appears tohave maintained its original installed state of hydraulicintegrity. The free swell of the bentonite has reduced, yet

continued...Performance of GCL in Landfill Applications

PAGE 11

not as significantly as the GCL samples taken from thecapping system.

SOIL ANALYSIS

The soil adjacent to the GCL was sampled at the samepoint as the GCL. The soil in the capping system had apH ranging from 7.4 to 7.5. The pH of the soil in thebasal lining system in Cell 1 had a pH ranging from7.7 to 8.3. The conductivity of the soil in the cappingsystem ranged from 30 mS/m to 60 mS/m.

The results of Atomic Absorption Spectrometry identifiedthe presence of Calcium (Ca+), Potassium (K+), andMagnesium (Mg2+) cations within a Sodium rich ClayMineral, indicating possible isomorphic substitution ofcations and cationic exchanges within the tetra octahedrallayers of the Bentonite.

CONCLUSION

There has been a deterioration of the GCLs hydraulicconductivity in the capping system (mid-reach ofembankment only) and essentially no loss in the basallining system. All tested GCL samples still meet theminimum hydraulic conductivities required by MinimumRequirements for Waste Disposal by Landfill, afterapproximately six years of service.

This study supports further investigation of soils usedin conjunction with GCLs for each site-specific condition.end...Performance of GCL in Landfill ApplicationsR.C.Emery. Jeffares & Green (Pty) LtdB. Makgekgenene. Jeffares & Green (Pty) Ltd

wishes you a happy & safefestive season

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PAGE 12

Case 2 Waste Water Treatment PlantA 6 ha WWTP lagoon used an unreinforced GCL on thefloor and a reinforced GCL on the slopes. Both hadmembrane films laminated to them. When the lagoon wasfilled it started leaking about 2.3 Ml per day. It was emptiedand some repairs made but the leakage did not stop. It wasemptied and investigated 2 years after first filling. Whenlitigation was initiated it was thoroughly investigated another2 years later.

There was about 300 mm of clayey sand on top of the GCLand 150 mm of 19 mm crushed aggregate under the GCL.Both GCLs had been placed with the membrane film down.The membrane had been punctured, the GCL had beenpunctured, and the bentonite laterally displaced. Notunexpectedly damage was more prevalent in the unreinforcedGCL on the floor.

The situation would have been better had the GCLs beenplaced with the film up, as is the case with most compositeliners — geomembrane on top, GCL or compacted clay linerunderneath. This way the more impermeable component,the film, would not have been punctured first. The GCLwould have cushioned the membrane and the geomembranecould have imparted the full hydrostatic head (~4 m) tothe confining pressure of the GCL, had the subgrade notbeen so rough with aggregate peaks and void space betweenthem.

When the water and soils were analyzed it was clear thatsignificant cation exchange of sodium for calcium hadoccurred (after 4 years) but this was not considered to bea major contribution to the initial leakage since suchexchange does not occur immediately.

SummaryFor a GCL to act as an impermeable barrier it must beinstalled with a uniform confining pressure. That meansno angular particles and significant void spaces on eitherside. This is the primary objective. Leak drainage capabilitymust be considered to be secondary and must notcompromise the primary function. When a composite GCLis used, unless there are other good reasons, it should bedeployed with the membrane uppermost.

Figure 1. Hole in GCL with bentonite eroded away

Figure 2. Subgrade aggregate and punctures in floor membrane.

What Not todo with GCLsBy Ian Peggs, Ph.D., P.E., P.Eng., DABFETPresident, I-CORP INTERNATIONAL, Inc.8 September 2009

Geosynthetic Clay Liners work extremely well when installedproperly but I have seen many installation mistakes. Themain one is correctly recognizing that all single liners leakto some degree and attempting to put a coarse subgradedrainage layer immediately underneath the GCL. Thus aGCL may be correctly covered with soil/sand ballast layerto provide the required confining pressure but it will beunderlain by a drainage layer of 19 or 25 mm angularaggregate. Consequently the GCL is punctured, bentoniteis laterally displaced and unacceptable leakage occurs.Thus there can be two conflicting requirements —imposinga uniform confining pressure on the GCL, and providing adrainage medium (with void spaces) underneath it. Thetwo are often achieved in an incompatible way. Let s lookat two case histories.

Case 1 Decorative pondAn 800 m2 1 m deep pond with a GCL liner was leakingabout 150,000 litres of water per day. When investigatedthe GCL was found to be placed on a 150 mm drainagelayer of slatey stone with particle size ~20 mm. There wasa monolayer of pebbles on top of the liner since the designerdid not appreciate the need for a confining pressure.In addition there were many limestone rocks in and aroundthe pond. The subgrade punctured the lower geotextile inmany places and the bentonite eroded away. There wasno chance for the bentonite to seal any holes since it wasalready fully hydrated and expanded. Although not testedion exchange of sodium ions in the bentonite by calciumions from the limestone was a given. Even if there had beena uniform compacted subgrade under the GCL sealingwould still not have occurred, due to the lack of confiningpressure. Conversely to what many people think, thehydrostatic pressure on the GCL does not provide therequired confining pressure.

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PAGE 13

Figure 1 - Swell index test, target swell 24ml/2g.

by ASTM D 5890 and ASTM D 5891 respectively. Thetest results may be compared to correlations of the indexin question and long-term hydraulic conductivity, providinga rapid and cheap method to assess compatibility andpossibly exclude the use of GCLs with aggressiveleachates.

Site specific leachates will not necessarily be availableat design stage, except in the case where design is forextensions to, or replacements for, existing landfill sites.In the case of a new site where leachate has not yetbeen generated, designers are cautioned that bentonitecompatibility testing with synthetic leachates may be anun-conservative approach, or may even be overlyconservative. In addition, making judgements ofcompatibility based purely on chemical composition ofthe leachates should be avoided, as experience hasshown apparently similar leachates to produce significantlydifferent swell indices with different bentonites.

The GIGSA newsletter publishesthemed content on a quarterly basis.

Make sure that you get your submissions inbefore the deadlines indicated below:

The GIGSA newsletter publishesthemed content on a quarterly basis.

Make sure that you get your submissions inbefore the deadlines indicated below:

March 09

June 09

November 09

TBA

Testing, Analysis, Design & Quality

Reinforcement & Stabilisation

Environmental Protection including Waste Containment

Hydraulic and Coastal Applications

Complete

Complete

Current Edition

TBA

Publication Date Submission Deadline

*If you require theme descriptions, please contact the Editor

Theme

Deadlines for Submissions

Index testing :a designer s toolBy: David JohnsJones & Wagener

Geosynthetic clay liners (GCLs) achieve their lowpermeabilities by virtue of their ability to undergo swellingof the bentonite clay when wetted, thus restricting porespaces and limiting the flow of water. However, theswelling capacity of the bentonite clay may be adverselyaffected by contact with the leachate intended to beretained. Leachates with high concentrations of cations,particularly multi-valent cations such as Ca2+, Mg2+ andFe3+, may, by the process of cation exchange, result inclay particles with significantly reduced hydrated radii.This manifests on the macroscopic scale as reducedswell. The pH of the leachate also plays a role in affectingswell and therefore in the hydraulic conductivity of thebentonite.

It is imperative that designers check compatibility of thebentonite component of any GCL with the site specificleachate. This can be done by several methods: the mostobvious of which is a permeameter test (ASTM methodsD 5887 and D 6766). However, these tests are oftenterminated too early, resulting in un-conservative estimates(up to one and a half orders of magnitude) of long-termhydraulic conductivity being made. On the other hand,reliable results from tests conducted with appropriatetermination criteria can take impractically lengthy periodsof time to complete. More rapid, although only qualitative,methods to assess compatibility of GCL bentonites withleachates are by index tests, for example the swell indextest (see Figure 1), and the fluid loss test, as prescribed

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PAGE 14

Published by GIGSA

c/o P.O. BOX 8720, EDENGLEN, 1620

www.gigsa.org

DisclaimerThe Geosynthetics Interest Group of South Africa and the South African Instituteof Civil Engineering accept no responsibility for any statements made or opinionsexpressed in this publication. Consequently nobody connected with the publicationof the magazine, in particular the proprietors, the publishers and the editors,will be liable for any loss or damage sustained by any reader as a result of hisor her action upon any statement or opinion publishedin this newsletter.

B e n e f a c t o r C o m p a n i e s

The Reinforced Earth Company

Maccaferri SA

Geotechnologies

GAST

Safyr

Engineered Linings

Kaytech

Aquatan

Geotextiles Africa

SRK Consulting

Jones & Wagener

Du Pont SA

Gundle Geosynthetics

ARQ Consulting Engineers

www.safyr.co.zaPO Box 20 Hammarsdal, 3700

Tel: (031) 736 7100 Fax: (031) 736 7115

www.englining.co.zaPO Box 36614, Chempet,7442

Tel: (021) 551 2430 Fax: (021) 552 5928

www.kaytech.co.zaPO Box 116, Pinetown, 3600

Tel: (031) 717 2300 Fax: (031) 702 3173

www.aquatan.comPO Box 633, Isando, 1600

Tel: (011) 974 5271 Fax: (011) 974 4111

[email protected] Box 5930 Boksburg, 1461

Tel: jhb(071) 678 7650 cpt(021) 701 3569

www.srk.co.zaPO Box 55291 Northlands, 2116

Tel: (011) 441 1111 Fax: (011) 441 1147

www.jaws.co.zaPO Box 1434, RIVONIA, 2128

Tel: (011) 519 0200 Fax: (011) 5190201

http://www2.dupont.com/South_Africa_Country_Site/en_ZA/index.html

PO Box 3332, Halfway house, 1685Tel: (012) 683-5600 Fax: (012) 683 5663

www.gundle.co.zaPO Box 455, Springs, 1560

Tel: (011) 813 2180 Fax: (011) 813 2189

www.arq.co.za6 Daventry St Lynnwood Manor, 0081

Tel: (012) 348 6668 Fax: (012) 348 6669

www.recosa.co.zaPO Box 91231, Auckland Park, 2006

Tel: (011) 726 6180 Fax: (011) 726 5908

www.maccaferri.co.zaPO Box 15777, Westmead, 3608

Tel: (031) 700 8456 Fax: (031) 700 8469

PO Box 2045, Rivonia, 2128Tel: (011) 234 8770 Fax: (011) 234 3713

www.gast.co.zaPO Box 9516, Hennopspark, 0046

Tel: (012) 660 1616 Fax: (012) 660 2093

Editor

Shakira Sattar

[email protected]

Tel: 031 202 4400

Design

Lionel Govender, Durban

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