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Designconsiderationsforgeosynthetic clay liners (GCLs) ingeosyntheticclayliners(GCLs)inheapleachpadlinersystemsC. Athanassopoulos, PECETCO, USA
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M. Smith, PERRD International Corp, USA
September25,2013
Liner Applications in Heap LeachingGeomembraneshaveaproventrackrecord,butarevulnerabletopuncturedamage
LinerApplicationsinHeapLeaching
InHeapLeachPads,puncturesserveasopenpathwaysforlossofPregnantLeachSolution(PLS):
SmithandWelkner (1995)estimatedlinerleakageratesrangingfrom5to10,000L/ha/day
ThielandSmith(2003)reportedupto2,000L/ha/dayforonevalleyfillwithhighheads
Liner Applications in Heap LeachingLinerApplicationsinHeapLeachingToreduceleakagethroughdefectstheGMcanbeplacedoveralowpermeability soil as part of a composite liner system:permeabilitysoil,aspartofacomposite linersystem:Compactedclaywithk=106 cm/sor107 cm/s;ORGeosyntheticclayliners(GCLs),sodiumbentonitebasedlinerswithky y ( )=5x109 cm/s
Claycomponentwillplugdefectsorpuncturesinthegeomembrane,reducingoverallleakage
Low Permeability SubgradeLowPermeabilitySubgrade
Smallerwettedarea,limitsPLSfromspreadingoutl lllaterally.
High Permeability SubgradeHighPermeabilitySubgrade
Landfill Liner Leakage RatesLandfillLinerLeakageRates
Source: Bonaparte, Daniel, and Koerner. (2002) Assessment and Recommendations for Optimal Performance of Waste Containment Systems, EPA/600/R-02/099. USEPA, ORD, Cincinnati, OH
NOT like LandfillsNOTlikeLandfillsScaleofoperationsisawesome: Finalheapheightsashighas200mFinal heap heights as high as 00 m Resultinginenormousnormalstresses(upto3500kPa) Steepslopes1.4H:1V,approx.36
Combinationofhighnormalstresses,overstressingofGMnexttopipes,largeangularrockinoverlinerandsubgrade,hightemperatures,andaggressiveleachingsolutions
Pushesthelimitsoflinermaterials
Requiresspecialdesignconsiderations
HeapLeachPadTechnicalConsiderations
GCL Chemical Compatibility with
Considerations
GCLChemicalCompatibilitywithMineLiquids(includingpHeffects)
GeomembraneandGCLPuncturePerformance
GCLShearStrengthandSlopeStabilityStability
GCL Chemical CompatibilityASTMD6766,StandardTestMethodforE l ti f H d li P ti f
GCLChemicalCompatibility
EvaluationofHydraulicPropertiesofGCLsPermeatedwithPotentiallyIncompatibleFluids
ModifiedversionofD5887andD5084(shoppressandfixedwallpermeameter)
Termination criteria for chemicalTerminationcriteriaforchemicalequilibrium:E.C.In E.C.OutpHIn pHOut
GCL Permeability with Gold/Silver PLS
1E-7
GCLPermeabilitywithGold/SilverPLS)
GoldPLS NaCN = 600 ppm
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Compatibility with extremepH LiquidsCompatibilitywithextreme pHLiquids
BentonitecanhandleawidepHrange3 12
Strongacidattacksthel t it tclayorconvertsittononswellingform
MetalsaremoresolubleatlowpH
Jo H Y Katsumi K Benson C H and T Edil (2001) Hydraulic Conductivity and Swelling of NonprehydratedJo, H.Y., Katsumi, K., Benson, C.H., and T. Edil (2001), Hydraulic Conductivity and Swelling of NonprehydratedGCLs Permeated with Single-Species Salt Solutions, Journal of Geotechnical and Geoenvironmental Engineering, 127 (7): 557-567.
GCLPermeabilitywithCopperPLSy pp
pH=1.7p ElectricalConductivity=
37,000uS/cm Aluminum = 5,044 ppmAluminum 5,044ppm Calcium=262ppm Copper=800ppm
I 1 788 Iron=1,788ppm Magnesium=498ppm Zinc=198ppm
Source: Athanassopoulos et al (2009).
BentonitePolymer AlloysBentonitePolymerAlloysNewclaypolymernanocompositeswithimproved 1.00E-04
tolerancetolowpH,highionicstrengthsolutionshavebeendeveloped
1.00E-07
1.00E-06
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RecenttestswithUraniummilltailingssolution(pH
HighLoadStaticPunctureTesting16staticpuncturetests,atloadsof:
Testing
1300kPa2580kPa3450 kPa3450kPa5170kPa
FS = 1 5 for ore heights of:FS 1.5fororeheightsof:45m90m120m180m
Source: Athanassopoulos et al (2009)
BenefitofGCLUnderneathGM(5172kPa,or180m)
GMalone8.5%typicalstrain25.7%peakstrain
3
GM/GCL1.6%typicalstrain3.0%peakstrain03punctures 0punctures
BenefitofGCLunderGM:Deformation MeasurementsDeformationMeasurements
GeomembraneDamageduringShearing
Constructionloading,oreplacement,seismicforces,orsettlementcancausesheardisplacement
TestingatUCSanDiegofoundGMis vulnerable to shearinducedisvulnerabletoshearinducedpuncturedamageathighnormalstressI l di GCL b t th IncludingaGCLbetweenthegeomembraneandthesubgradesoilcanessentiallyeliminatesuchd t l tdamage,evenatnormalstressesashighas4144kPa(150moforewithFS=1.5)
Athanassopoulos et al (2012). Shear-Induced Geomembrane Damage due to Gravel in the Underlying Compacted Clay Liner Underlying Compacted Clay Liner. GeoAmericas 2012.
DirectShearTestingofGeomembrane/GCL
SheardeviceatUniversityofCaliforniaSan DiegoCalifornia SanDiego
Testchamber=152x1067mmMaxnormalstress=4,144kPa
Doublenonwoven,needlepunchreinforcedGCL
testedagainstBlownfilmcoextrudedtexturedGM
Source: Athanassopoulos, Fox, and Thielmann (2012), EuroGeo5
Sand(Subgrade)
GCL HDPEGeomembrane
Gravel(Overliner)
GM/GCLInterfaceatUltrahighloads(4,145kPa)
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Peakfrom2013study
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LDfrom2013study 200mmPeakfrom2009studyLDfrom2009study 75mm
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NormalStress,n (kPa)Thielmann et al (2013);Athanassopoulos et al (2009)
ApplicableStressRanges
Liner Systemf,2n 2
f,1n,2n,1
f,2
f,1c2,
c1,1n,2n,1
LowLDfrictionangleswilloccurunderthedeepestpartoftheheap.Therewillbemuchhigherf i i l i h i i l bili d h d h f ifrictionanglesinthecriticalstabilityzonetowardsthetoe,andthereforegreaterresistancetosliding.
BreitenbachandSwan(1999)( )
IncreasedShearStrength(~5degrees)duetoGMDimplingunderHighNormalStress
ImprovingHeapLeachPadStabilitySpeedBumps
Source:BreitenbachandAthanassopoulos(2013)
Source: Comanco
Example stability berm configuration from a heap leach pad liner projectExamplestabilitybermconfigurationfromaheapleachpadlinerproject.
ImprovingHeapLeachPadStabilityp g p yStairStepberms
Source:BreitenbachandAthanassopoulos(2013)
Source: Allan Breitenbach
Stair step pattern on back slope
Source:AllanBreitenbach
Dependingonlocalterrain,incorporatingnaturalundulationsofStairsteppatternonbackslope.sitesubgradeintogradingplanmayreducecost.
HLPFeasibilityStudy ExampleGM/compacted
soilGM/GCL
Leakage (L/ha/day) 1 929 203Leakage(L/ha/day) 1,929 203
CopperinPLS(ppm) 3,000 3,000
Copper lost due to leakage 2 113 222Copperlostduetoleakage(kg/ha/yr)
2,113 222
Copperprice(Sept2013)($/kg) $7.06 $7.06pp p p g
Costofcopperlost($/ha/yr) $14,910 $1,590
Gain in Revenue ($/ha/yr) $13,340GaininRevenue($/ha/yr) $13,340
BenefitCostRatio(PV,i =10%,n=15years,claycost=$4.30/m2,GCLcost=$5.90/m2) 6.3
GCLsinHeapLeachPads Summary ChemicalCompatibility.GCLsarecompatibilitywithCNleachsolutions.GCLpermeabilitycanbeaffectedbylowpHsulfuricacidleachsolutions;
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however,increasednormalstressmitigatestheseeffects.
PunctureProtection.GCLscancushiongeomembrane from stones in both the overlinergeomembranefromstonesinboththeoverlinerandsubgrade.
ShearStrengthandSlopeStability. GM/GCLinterfaceshavehighpeakstrengths,butg p g ,potentiallylowLDstrengths.However,incorporatingnonplanarfeaturesinthesubgrade(e.g.,speedbumps)canimprovestability,eveninworstcase conditions (7 degrees)worst caseconditions(7degrees)
FeasibilityStudy.ImprovedPLScontainmentprovidedbyGCLoverlifeofprojectwilloftenmorethanoffsettheinitialcostofGCL.
ThankyouQ ti ?Questions?C.Athanassopoulos,PECETCO,USAcatha@cetco.com
M.Smith,PERRDInternationalCorp,USApmark.smith@rrdintlcorp.com