upgrade of aircraft apron - pavement design

ACASESTUDY-UPGRADEOFTHETERMINALAPRONATMUMBAIINTERNATIONALAIRPORT

By:PaulMcCullaghandManojTipnis

Larsen&ToubroLimited,EngineeringConstruction&Contracts(ECC)DivisionGate1,NorthBlock2,PowaiCampus,SakiViharRoad

Mumbai,MH400072,IndiaPhone:+912228581401;Fax:+912228581401

[email protected]@Lntecc.com

PRESENTEDFORTHE2010FAAWORLDWIDEAIRPORTTECHNOLOGYTRANSFERCONFERENCE

AtlanticCity,NewJersey,USA

April2010

McCullaghandTipnis 1

INTRODUCTION

ChattrapatiShivajiInternationalAirport(CSIA)atMumbai,India,currentlyhandlesinexcessof21millionpassengersand465,000metrictonnes(512,500Tons)ofcargoperannum.Thesefiguresareforecasttogrowto40millionpassengersand1millionmetrictonnes(1.1millionTons)ofcargoperannumby2015.

InApril2006,MumbaiInternationalAirportPrivateLimited(MIAL)signedanOperational,ManagementandDevelopmentAgreementwiththeAirportsAuthorityofIndia(AAI)tooperate,maintain,develop,design,construct,upgrade,modernize,financeandmanagetheairportforaperiodof30years,withanextensionoptionforafurther30years.In2007,Larsen&ToubroLimited,ECCDivision(L&T)wereawardedacontractbyMIALtoupgradetheairportaspartoftheCSIAExpansionandRenovationProgram.MIALisajointventurecompanyownedbyaGVKGroupconsortiumandAirportsAuthorityofIndia(AAI).

AspartoftheCSIAExpansionandRenovationProgram,theexistinginternationalterminalandtheassociatedapronsarebeingreplaced.Theprojectconsistsofthereplacementofapproximately540,000m2ofexistingrigidpavementswithover950,000m2ofnewpavement.Theapronswillbeinusethroughoutthe3yearconstructionperiod,andarecurrentlyoperatingnearsaturationtrafficlevels.Detailedstaginghasbeenimplementedtoachieveabalancebetweentheoperationaluseoftheapronsandadequateworkfacestoachieveconstructionefficiency.Theprojecttimelineisfurthercomplicatedbyanannualmonsoonperiodoffourmonthsduration.

ThereconstructedapronshavebeendesignedtoICAOstandardsutilizingFAARFIELDsoftwareforpavementdesign.GeometricandpavementdesignsweredesignedinaccordancewithICAOAnnex14[1]andICAOAerodromeDesignManualParts1,2and3[2,3,4].FAAAdvisoryCircular150/5320-6E[5]wasusedasaguideforpavementdesignsanddetailing.

TheforecastusageforeachaprontaxilaneandaircraftstandwasanalyzedandpavementthicknessesweredeterminedusingFAARFIELD.Theaircraftparkingstandsweredesignedusingfewerdeparturesbutwithcorrectionfactorstocaterforreducedwander.Bothdesignsgavesimilarresults,henceauniformpavementthicknesswasadoptedthroughout.

Themajorityofthenewapronfootprintrestsoverexistingconcreteandflexiblepavementswhichwillbeusedasafoundationforthenewrigidpavementstoeconomizethedesignandexpediteconstruction.Theapronrequiresverticalshapecorrectionwhichleadstovaryingdegreesofcutandfillovertheexistingsurface.Theexistingapronpavementwillbereusedinanumberofways,includingrubblizationoftheexistingconcretepavements,recyclingofotherconcretepavementsforuseassubbasewhererubblizationisnotfeasible,andremovaloftheexistingwearingcoursesandutilizationoftheunderlyingpavementcoursesassubbase.Wherenoneofthisispossibleduetoinadequatecoveroversubgrade,newfulldepthpavementshavebeenadopted.

Thesubbaseforthenewconcretepavementsisthereforeamixtureofrubblizedconcrete,existingsubbaseandnewsubbase.Utilizingrubblisedconcreteasasubbasefornewrigidpavementsisahighlightoftheproject.


EXISTING&PROPOSEDAPRONLAYOUTS

Therunways,taxiwaysandapronsatCSIAarecurrentlycertifiedforusebyICAOCodeE(FAAAirplaneDesignGroupV)aircraft,howeversomemovementareasarebeingupgradedtoICAOCodeF(FAAADGVI)requirementsaspartofthisproject.CSIAcurrentlycatersforaround21millionpassengersperannumand550aircraftmovements(arrivalsanddepartures)perday,splitbetweenadomesticterminalcomplex(T1)andaninternationalterminal(T2).Atthecommencementoftheproject,theoriginalinternationalterminal(T2)wasaconvexshapedsingleconcoursebuildingwith14CodeEcontactstands.ThegreaterT2apronalsoprovidedafurther15CodeD/E(ADGIV/V)and6CodeC(ADGIII)remotestands.Thisgaveatotalof35standsontheexistingapronatthecommencementoftheproject.

AspartoftheCSIAExpansionandRenovationProgram,theexistingT2buildingandapronarebeingreplacedwithanewx-shapedintegratedterminal(with3convexshapedfaces)thatwillbeusedforbothdomesticandinternationaloperations.Intheinitialphaseofdevelopmentdueforcompletionin2013,thenewapronwillprovide3CodeF(ADGVI),40CodeE(ADGV),0CodeD(ADGIV)and5CodeC(ADGIII)stands,givingatotalof48standsonthenewapron.Duringthepeakdomestictimes,17ofthelargercontactstandscanbeconvertedona2for1basisintoCodeCstands.Theremoteapronsalsocanconvert11CodeEstandsinto21CodeCstands.Inthefinalphaseofdevelopmentatotalof38CodeE/Fcontactstands,14CodeE/Fremotestandsand19CodeCremotestandswillbeprovided(total71stands).

Theorientationoftheexistingandproposedterminalbuildingfacesdiffersignificantly(byupto90degrees),whichmeansthattheexistingapronpavementscouldnotberetainedforusewiththenewbuildingduetoincorrectorientationofslopes,drainageandundergroundservicesandageneralleveldifferencebetweentheexistingandproposedterminalbuildings.Theproposedaproncoversanareaofapproximately950,000m2(10,225,000ft2).

CONSTRUCTIONSTAGING

Thelocationofthenewinternationalterminalbuildingsitsdirectlyonthesiteoftheexistingterminalbuilding,carparkandapron.Atthecommencementoftheproject,theairportoperatordeclaredthattheexistingterminaland24widebodyparkingstandsmustremainoperationalthroughoutthedurationoftheproject,hencetheterminalandaprondevelopmentsmustbeconstructedinaseriesofdiscreetstagesinordertomaintainairportoperations.Thenewpavementsareplannedtobecompletedbymid2013.ThisisadifficulttaskgiventhatMumbaiexperiencesaheavytropicalmonsoonperiodforfourmonthsperyear(JunetoSeptember)whicheffectivelyhaltsallcivilworks.Thisleavesaround32monthstocompletethepavementworks,atarateofnearly30,000m2(325,000ft2)permonth.

Numeroustemporaryparkingstandlayoutswereanalyzedduringtheinitialdesignphaseoftheprojectinordertodeterminehowmanyoftheexistingparkingstandscouldbetemporarilyrelocatedtofreeupspaceforconstructionofthenewapron,taxiwaysandterminalbuilding.Anadditional3widebodyparkingstands(2contactand1remote)wereconstructedontheeasternsideoftheexistingapronatthecommencementoftheprojecttoprovidesomeflexibilitytoshuffleparkingstandsduringtheworks.Evenwiththisadditionalcapacity,amaximumofonly5existingwidebodystandscouldbedecommissionedduringtheinitialconstructionstages.


Giventhatlimitedspacewasavailableontheinternationalapronfortemporaryparkingofwidebodyaircraft,theconstructionstagingsequencingwaslimitedtoshufflingbetweensmallareas,andcommissioning/decommissioningsmallnumbersofstandsatthecompletionofeachstage.Forexample,duringthefirsthalfoftheproject,parkingstandswerecommissionedingroupsof3,2,1,4,4,3and5atthecompletionofeachstage.

Atotalof15constructionstageshavebeendesignedfortheproject,asshowninFigure1below.Eachstagerequiredcarefulplanningofairportoperations,siteaccessroutes,safetymarkings&barricadesaswellasdetailedplanningoftheconstructionsequencingandcommissioningscheduletoenableaeronauticalchartsandNOTAMstobepublishedwellinadvanceoftheworks.

Theconstructionstagingledtooptimizationofaircrafttaxiwaysandassociatedsafetyclearancesinordertomaximizetheconstructionworksarea.Althoughthisexercisewaslargelysuccessful,someworkshadtobeplannedtobeundertakenonatimelimitedbasiswithinthetaxiwaystrips.Underthisprocedure,menandequipmentwouldenterthestripundersupervisionofworkssafetyofficers,andwouldvacatetheworkssiteforeachwidebodyaircraftmovement.

ItshouldbenotedthattheinternationalapronredevelopmentispartofthewiderCSIAExpansionandRenovationProgram,whichincludesmajorwidening,strengtheningandshapecorrectionofbothoftheairportscrossrunways,realignmentofthemainparalleltaxiwaytoCodeFclearances,constructionofover625,000m2(6,725,000ft2)ofnewtaxiwaypavement,aswellas12km(7.5miles)ofnewopendrainsandboxculverts,anewairfieldgroundlightingsystemwithover5,000newlightsand500km(310miles)ofcabling,and60km(37miles)ofnewAGLandelectricalductbanks,allwithinthesametimeperiod.Asaconsequence,theT2constructionstagingalsohadtobecognizantoftheimpactontheairportoperationsandworksareasfortheremainderoftheairport.

EXISTINGPAVEMENTS

The new apron area is located over varying terrain including existing flexible & rigidpavements, former building sites and grass areas. All the existing contact and remote aircraftparkingstands are rigidpavements, apron taxilanesareamixof flexibleand rigidpavements,andgroundserviceequipmentstorageareasaregenerallyreducedstrengthflexiblepavements.

Extensivegeotechnicalinvestigationswereundertakenwithanaimtoestablishthestructureof all existing pavements and to determine the subgrade classification and strength across theentireapron.Atotalof45boreholeswereundertakenontheexistingpavements todeterminethe USCS materials classification and thickness of each pavement layer. Standard PenetrationTests(SPT)wereconductedonthesubgradethrougheachboreholetodeterminetheNvalueswhich could be correlated to provide subgrade E modulus, CBR & coefficient of subgradereaction(k)valuesforpavementdesignpurposes.Asthepavementshavebeeninplaceformanyyears,itwasagreedthatthesubgradewasatanequilibriumstateandthatfieldsubgradereactionwas a better option to laboratory derived values. A limited number of plate load tests andlaboratory CBR tests were conducted to verify the correlations used to calculate CBR and kvaluesfromthefieldmeasuredNvalues.Theplateloadtestingwasparticularlylimitedduetooperationalrestrictionsattheairport.


Figure1.T2ApronConstructionStages(Notallstagesshown).


The3mainpavementsidentifiedbythegeotechnicalinvestigationwere:

Rigidaircraftpavements

Flexibletaxilanepavementsand

GroundSupportEquipment(GSE)flexiblepavements

Theexistingrigidpavementsareofvariousages,rangingfrom3to30years.Theolderrigidpavements are presently in various stages of deterioration, with longitudinal and transversecracks as well as edge spalls and corner breaks noticeable on around 30% of existing slabs.Differential settlement (faulting) is also evident across some slabs, up to 15 mm (0.5). TheexistingrigidtaxilaneandaircraftparkingstandpavementshavePCCvaryinginthicknessfrom400mm(15.75)to600mm(23.5)withEmodulusvaluesinrangeof16,000MPa(2,320,000psi) to 22,000 MPa (3,190,000 psi). The E modulus values were estimated by compressiontestingextractedcoresasper IndianStandardIS-516(equivalent toASTMC469).ThePCCisgenerally constructed over a 150 mm (6) thick stabilized base layer of Dry Lean Concrete(equivalent to P-304) over 600 mm (23.5) to 1,000 mm (40) thick granular subbase(equivalent to P-154). The minimum pavement thickness analyzed for design purposes was400mm (15.75) P-501 PCC on 150mm (6) P-304 CTB on 850mm (33.5) P-154 granularsubbase.Thetotalpavementthicknessis1,400mm(55).

Theexistingflexiblepavementsdonotshowanymajorsignsofdistress,apartfromroutinesurfacedefectsrequiringongoingmaintenancesuchasoxidation,ravelingandminorbleeding.Theexistingflexiblepavementsconsistofapproximately650mm(25.5)ofasphalticconcretewearing course / base course (P-401) over approximately 750 mm (29.5) granular base /subbase(P-209andP-154).Thetotalpavementthicknessis1,400mm(55).

Theborelogsestablishedthepresenceofrockstrataunderthepavementatdepthsvaryingfrom1,750mm(69)onthewesternsideoftheapronto5.5m(18ft)ontheeasternside.ThesubgradelayerabovetherockstrataconsistsofresidualsoilwhichhasbeenclassifiedasSiltyClaywithlowtohighplasticity(USCSCLCH).ThecorrelatedCBRcalculatedfromfieldNvaluereadingsforthesubgradesoilvariedfrom1.6%to2.5%.Thewatertableintheareavariesseasonallybetween2m(6.5ft)to3m(10ft),asperthePeisometerreadingstakenovertheyear2008-2009.Fordesignpurposes,asubgradeCBRvalueof2%andakvalueof11kPa/mm(40pci)wereadopted.

SUBBASEPREPARATIONOPTIONS

ThenewinternationalapronistobeconstructedfromrigidPortlandCementConcrete(PCC)pavement,withtheexceptionoftheheadofstandroad,groundserviceequipmentstorageareasandtaxiwayshoulders,allofwhichwillbeconstructedfromasphalticconcretesurfacedflexiblepavement.Rigidpavementsarepreferredfortheaircraftparkingstandsandtaxilanesduetotheveryhighstressesthatheavilyweightedslowmovingandstaticaircraftplaceonthepavement,andduetofuelandoilspillsthatcanoccurfrommaintenanceandrefuelingoperationsontheapronstands.


Thefootprintofthenewapronliesoverexistingflexible&rigidpavements,formerbuildingssitesandgrassareas.Thelevelsoftheproposedpavementsvarysignificantlyfromtheexistinglevels,withthemajorityoftheareasneedingtoberaisedtomeetthedesignprofile.Assuch,itbecameevidentthatalargequantityoftheexistingpavementscouldbereusedassubbaseforthenewapronpavementinordertoprovideaneconomicalalternativetofulldepthreconstructionoftheentireapron.Fulldepthreconstructionwouldonlyberequiredinareascurrentlyoccupiedbybuildingsorgrassislands,orinareasofcutwhereinsufficientcoveroversubgradecouldnotbeachieved.

Anumberofoptionswereinvestigatedforeconomicalreuseoftheexistingpavements,includingreuseofexistingintactpavements,bonded&unboundedconcreteoverlays,cracking&seatingofexistingPCCpavements,rubblizationofexistingPCCpavements,reuseofexistingsubbaseandrecyclingofPCCandasphalticconcretematerials.Thefollowingparagraphsdiscussthetechnicalmeritsofeachofthesubbasepreparationoptionsconsideredinthedesign.ThepavementsectionsadoptedforpavementthicknessdesignareshowninTable1below.

ReuseofExistingIntactPavements.Intactexistingpavementscouldonlybereusedinareaswheretheproposedlevelsmatchedtheexistinglevels,andprovidedthattheconditionandstructuralcapacityoftheexistingpavementswouldprovideanadequatedesignlifewithoutsignificantmaintenanceorreplacement.Afterreviewingthesefactorsitwasdecidedthattheareasthatcouldbereusedwereinsufficienttowarrantimplementationofthisoption.

BondedConcreteOverlays.Bondedconcreteoverlayscouldbeusedwheretheexistingrigidpavementswereinverygoodcondition,wherethejointpatternoftheexistingslabsmatchedtheproposedjointlayoutofthenewpavement,andwheretheverticalgeometricprofileoftheproposedsurfacematchedtheexistingsurfaceprofile,toavoidvaryingthicknessesoftheoverlay.Afterreviewingthesefactors,itwasdecidedthatthisoptionwasnotfeasible.

UnbondedConcreteOverlays.Unbondedconcreteoverlayscouldbeusedwheretheexistingrigidpavementswereinverygoodconditionandtheverticalgeometricprofileoftheproposedsurfacewassimilartotheexistingsurfaceprofile,toavoidthickasphalticconcreteprofilecorrectioncoursesbeingconstructedbetweenthetworigidpavements.Afterreviewingtherelativelevelsoftheproposedandexistingsurfaces,itwasdecidedthattheprofilecorrectioncourseswouldbeuneconomicalandunfeasible.

Cracking&SeatingofExistingPCCPavements.CrackingandseatingofexistingPCCpavementsisgenerallyutilizediftheoverlaymaterialisintendedtobeasphalticconcrete.Inourcase,theoverlaymaterialwasintendedtobePCC.Inordertoavoidasandwichpavement,theprofilecorrectioncoursewouldneedtobeastabilizedmaterialsuchasP-401asphalticconcreteorP-304cementtreatedbase.Notonlywasthiscorrectioncoursedeterminedtobeuneconomical,itwouldresultinanextremelystiffsubbaseonwhichtoconstructthenewPCC,whichcouldleadtoearly-agedistresssuchastop-downcracking.Afterreviewingthesefactors,itwasdecidedthatthisoptionwasnotfeasible.

RubblizationofExistingPCCPavements.RubblizationofexistingPCCpavementsisgenerallyutilizediftheoverlaymaterialisintendedtobeasphalticconcrete,andtherewerenoknownexamplesofnewrigidpavementsbeingconstructedoverarubblizedconcretepavement.


AftercarefulconsiderationitwasdecidedthattherubblizationprocesswouldshattertheexistingPCCslabssufficientlytoeliminatetheslabactionoftheexistingPCCpavement,therebyreducingthelikelihoodofreflectioncrackingfromtheunderlyinglayers.Sincetherubblizedmaterialiseffectivelygranularinnature,theprofilecorrectioncoursecouldbeconstructedfromgranularmaterials(P-209andP-154)withoutthesectionactingasasandwichpavement,andthereforethisoptionwasconsideredtobefeasible.

ReuseofExistingSubbase.TheexistingsubbasecouldbereusedinsituafterremovalofasphalticconcreteorPCCwearingcoursesprovidedthatthesubbasewasofsufficientthicknesstoprovidetherequiredcoveroversubgradeandofsufficientquality.Afteranalyzingthestrengthoftheexistingsections,itwasdecidedtoretainaminimumof600mm(23.5)ofexistingsubbaseunderthenewPCCandstabilizedbasecourselayers.Thisoptionwasconsideredtobemoreeconomicalandenvironmentallyresponsiblethanimportingnewsubbasematerials.Accordingly,thisoptionwasconsideredtobefeasible.

FullDepthReconstruction.FulldepthreconstructionwouldberequiredinareaswhereneitherrubblizationofexistingPCCpavementsorretentionofexistingsubbaseoptionswerefeasible.Thiswouldoccurinareasofcut,orareascurrentlyoccupiedbybuildings,shouldersandgrassislands.

RecyclingofPCCandAsphalticConcreteMaterials.InareaswhereexistingasphalticconcreteorPCCwearingcoursesweretoberemoved,recyclingofthematerialsforreuseasasubbasecoursewasinvestigated.VendorswereidentifiedthatcouldprovidemobilecrushingplantsonsitethatcouldcrushPCCandasphalticconcreteintoamaterialwithequivalentpropertiestosubbase(P-154)qualitymaterial.Asanalternative,theexistingasphalticconcretecouldberemovedbycoldmillingandthemilledmaterialcouldalsobeusedinlieuofP-154material.Bothmethodswereconsideredtobemoreeconomicalandenvironmentallyresponsiblethanimportingnewsubbasematerials.Accordingly,thisoptionwasconsideredtobefeasible.

Table1.PavementSectionsAdoptedforPCCThicknessDesign.

Layer PCCoverRubblizedConcretePCCoverExistingSubbase

PCCFullDepthReconstruction

WearingCourse P-501PCC P-501PCC P-501PCC

StabilizedSubbase 150mm(6)P-304CTB150mm(6)P-304CTB

150mm(6)P-304CTB

CrushedAggregateCappingLayer

200mm(8)P-209crushedaggregatebasecourse



ProfileCorrectionCourse

P-154(orequivalent)aggregatesubbase



Subbase/SelectFillRubblizedPCC,E=1,400MPa(200,000psi)andunderlyingsubbase

RetainedexistingP-154equivalentaggregatesubbase

900mmofSelectFillCBR6%

Subgrade k=11kpa/mm(40pci)k=11kpa/mm(40pci)

k=11kpa/mm(40pci)


AIRCRAFTTRAFFICANALYSIS

Therigidpavementsweredesignedfora30yearlife,andtheannualtrafficwasconsideredforboththetaxilanesandaircraftparkingstandstoenableacomparisonoftheresults.Thetrafficwasestimatedbasedonadetailedanalysisoftheaircraftparkinglayoutandpredictedoperatingmodesoftheapron.ThenewT2terminalbuildingwilloperateMultipleAircraftRampSystem(MARS)standsandswinggates,sothatasinglestandcanaccommodateeitheronewidebodyaircraftortwonarrowbodyaircraft,ineitherdomesticorinternationalconfiguration.Accordingly,theparkingstandswerecategorizedintothreemaingroupsbasedonthelikelyoperatingscenariooftheapronandterminalbuilding;dedicatedinternationalusage,dedicateddomesticusage,andmixedinternational/domesticusage.Inaddition,thetaxilanetrafficwassplitinto8differentsegmentsandtrafficwascalculatedaccordingtotheestimatedusageofstandsbeingfedfromeachofthe8taxilanes.ThelayoutoftheapronisshowninFigure2below.

CSIAcurrentlyhandlesapproximately550dailyairtrafficmovements(arrivalsanddepartures),howeverthisusageisforecasttoincreaseto888dailymovementsby2015.The2015forecastusagerepresentstheconstrainedcapacityoftheairport,hencetrafficisexpectedtoremainconstantafterthistime.ThemostlikelyaircraftfleetmixfortheairportwasdeterminedfromtrafficforecastreportscommissionedbyMIAL,andisshowninTable2below.

Figure2.T2ApronLayoutwithTaxilanesandOperationalScenarioGroups.


Table2.CSIAAircraftFleetMixPercentages.Aircraft A320 A321 A300 A330 A340-300 A340-600 A380FleetMix 16.7% 2.3% 10.7% 10.7% 4.1% 4.1% 0.3%

Aircraft B737-800 B767-400 B747-400 B747-8 B777-300 B777-300ER MD11FleetMix 26.0% 5.6% 5.9% 0.3% 8.2% 3.4% 1.8%

Theabovefleetmixwasnotapportionedtoaircraftstands,asairlinestendtohavepreferredstandsandsomestandsmaybeutilizedmorethroughoutadaythanothers.Consequently,regardlessofwhetherastandisusedforinternationalordomesticaircraft,thatstandmaybeusedtoservicealargemixofaircrafttypes,oritmaybeusedpredominantlytoserviceonlyafewaircrafttypes.Certainstandsoneachapronareamaybeallocatedtothepredominantairlines(oraspecificramphandler),whichmayoperatealimitedfleetrange.Hence,itisreasonabletoexpectthatastandmaybesubjectedtoregularusageofcriticalwideandnarrowbodyaircrafttypesratherthanthefullairportfleetmix.Basedonthefleetmixandflightschedulesprovidedbythecapacitystudy,itwasclearthatthemajordomesticoperatorswerefavoringB737-800andA320/1aircraft,andthemajorinternationaloperatorswerefavoringB777-300,B777-300ERandA330-300aircraft.Aftercarefulconsiderationofthesefactors,wedeterminedthatthefollowingfleetmixeswouldrepresentthemostlikelyworstcasetrafficsituationsfortheapron.

DedicatedInternationalFleetMix30%B777-300ER,40%B777-300,30%A330-300.

DedicatedDomesticFleetMix12.5%A330-300,12.5%B777-300,37.5%A321,37.5%B737-800.

MixedInternational&DomesticFleetMix4.3%B777-300ER,5.6%B777-300,4.3%A330-300,42.9%A321,42.9%B737-800.

Theannualtaxilaneusagewascalculatedforeachofthe8taxilanesbasedonthedailyairporttraffic,aircraftfleetmixandtaxilaneusagefactors.Thetaxilaneusagefactorsareexpressedasthepercentageofnarrowbodyandwidebodystandsthatcanbeaccessedviaeachtaxilane.Thefollowingformularepresentsthecalculationoftheannualtaxilaneusageforanygiventaxilaneandforanygivenaircrafttype:

365= tuffmdaa PPTT

Where: Ta = Annualdeparturesofparticularaircrafttypeforspecifictaxilane Tda = Totaldailyairportdepartures Pfm = Percentageofaircraftfleetmixapplicabletoaircrafttype Ptuf = Percentagebasedtaxilaneusagefactorforspecifictaxilane

ThecalculatedannualdeparturesforeachtaxilaneareshownTable3below:


Table3.AnnualDeparturesforeachTaxilane. P1a P1b P1c Ha Hb Hc M1a M1bA320 7,624 17,790 17,790 0 1,271 3,812 13,978 7,624A321 1,054 2,460 2,460 0 176 527 1,933 1,054B737-800 11,599 27,064 27,064 0 1,933 5,799 21,265 11,599A300 896 4,181 5,674 2,389 2,389 1,493 4,181 896B767-400 473 2,207 2,995 1,261 1,261 788 2,207 473A330 896 4,181 5,674 2,389 2,389 1,493 4,181 896A340-300 348 1,626 2,207 929 929 581 1,626 348A340-600 348 1,626 2,207 929 929 581 1,626 348B747-400 373 1,742 2,364 995 995 622 1,742 373B777-300 662 3,089 4,193 1,765 1,765 1,103 3,089 662B777-300ER 284 1,324 1,797 757 757 473 1,324 284A380 0 0 0 0 365 73 0 0B747-8 0 0 0 0 365 73 0 0

Theannualparkingstandusagewascalculatedforeachofthe3operatingscenariogroups(dedicatedinternational,dedicateddomesticandmixedinternational/domestic),basedonthedailystandusage,standfleetmixandPasstoCoverageRatiocorrectionfactor.FAARFIELDassumesanormaldistributionofaircraftwanderaboutthepavementcenterline,howeverthedegreeofwanderexperiencedonaircraftparkingstandsistypicallyverysmallduetotheuseofVisualDockingGuidanceSystemsandnose-wheelguidancecameras.Toaccountforthis,adjustmentsweremadetothetrafficfigurestoartificiallyaccountfortheinbuiltPCRfactorsusedbyFAARFIELD.

Internationalpassengeraircrafttypicallytakelongertoservicethandomesticaircraft.Asaworstcasescenarioaninternationalstandcouldservice8aircraftperday,adomesticstandcouldservice16aircraftperday,andamixedstandcouldservice14aircraftperday.Thefollowingformularepresentsthecalculationoftheannualparkingstandusageforanygivenoperatingscenariogroupandforanygivenaircrafttype:

365= PCRPTT fmsa

Where: Ta = Annualdeparturesofparticularaircrafttypeforspecificstand Ts = Totaldailystanddepartures Pfm = Percentageofstandfleetmixapplicabletoaircrafttype PCR = PasstoCoverageRatiocorrectionfactor

ThecalculatedannualdeparturesforeachoperatingscenariogroupareshownTable4below:


Table4.AnnualDeparturesforeachParkingStandOperatingScenarioGroup.

PasstoCoverageCorrectionFactor

DedicatedInternational

DedicatedDomestic

MixedInt.&Domestic

B777-300 4.13 4,824 3,015 1,206B777-300ER 3.86 3,381 0 845A330 1.88 1,647 1,372 412A321 3.46 0 7,577 7,577B737-800 3.53 0 7,731 7,731

PAVEMENTDESIGNUSINGFAARFIELD

DesignswereconductedusingFAARFIELDbasedontaxilaneandparkingstandtraffic,andtheresultsarepresentedinTable5andTable6below.

Table5.CalculatedPCCThicknessesbasedonTaxilaneTraffic.

RubblizationofExistingPCC

RetentionofExistingSubbase

FullDepthReconstructionTaxilane

mm Inches mm Inches mm InchesP1a N/A N/A 450 17.75 440 17.25P1b N/A N/A 485 19 475 18.75P1c N/A N/A 490 19.25 485 19Ha 335 13.25 470 18.5 460 18Hb 335 13.25 470 18.5 465 18.25Hc N/A N/A 460 18 455 17.75

M1a 380 15 480 19 475 18.75M1b 335 13.25 450 17.75 440 17.25


Table6.CalculatedPCCThicknessesbasedonParkingStandTraffic.



FullDepthReconstructionOperating

ScenarioGroupmm Inches mm Inches mm Inches

DedicatedInternational 375 14.75 485 19 475 18.75

DedicatedDomestic 325 12.75 445 17.5 435 17

MixedInternational&Domestic

N/A N/A 455 17.75 445 17.5

ThedesignPCCthicknessescomputedbasedontaxilanetrafficandaircraftstandtrafficwerefoundtobecomparable,andthereforeasperstandardpractice,thedesignthicknessesascomputedfortaxilanetrafficwereadoptedforboththetaxilanepavementsandadjacentparkingstands.

ConstructioncostscouldbeoptimizedbyadoptingvaryingPCCthicknessesforeachtaxilaneandadjacentparkingstands,howeverinviewofpracticalconsiderationsandsimplificationofformworkandconstructionmethodology,threestandardPCCthicknesseswereadoptedacrosstheapron.ThePCCthicknessesadoptedforconstructionwere400mm,450mmand485mmasperTable7below.AlthoughthethicknessescomputedforthenewPCCoverrubblizedexistingPCCsubbasewereintherange335mmto380mm(13.25to15),itwasconsideredprudenttoadoptaminimumPCCthicknessof400mm(15.75)inordertoallowforsomeconservatisminthedesignandtomitigateagainstpossibleadditionalwarpingandcurlingstressesassociatedwithathinnerpavementoveracomparativelystiffsubbase.

Table7.PCCThicknessesAdoptedforConstruction.



FullDepthReconstructionTaxilane

mm Inches mm Inches mm InchesP1a N/A N/A 450 17.75 450 17.75P1b N/A N/A 485 19 485 19P1c N/A N/A 485 19 485 19Ha 400 15.75 485 19 485 19Hb 400 15.75 485 19 485 19Hc N/A N/A 485 19 485 19

M1a 400 15.75 485 19 485 19M1b 400 15.75 450 17.75 450 17.75


PAVEMENTSECTIONSFORNEWRIGIDPAVEMENTS

Therelativecostsofeachfeasibleoptionwereconsideredindetail,includingthecostofplacingprofilecorrectioncoursesandthewearingcourseovertheinsitu/recycledsubbaseinordertoascertainthecostbenefitsofeachmethod.TheinitialbasiccostcomparisondeterminedthatinsiturubblizationofexistingPCCpavementswasthemosteconomicalsolution,followedbyretentionoftheexistingsubbasewithrecycledsubbasecorrectioncourses.Fulldepthreconstructionwastheleasteconomicalsolution.

Fromthepavementthicknessdesignanalysisitwasdeterminedthatthesubgradetreatmentoptionsweredictatedbytheexistingpavementstructureaswellastherelativeleveldifferencebetweentheexistingandproposedpavements.Thefollowingpointsweredeterminedfromtheanalysisforselectionofthemostappropriatepavementtypesforeachoftheapronareas:

RubblizationofexistingPCCpavementscouldoccurinareasofexistingrigidpavementswheretheleveldifferencebetweentheproposedandexistingsurfaceswasadequateforaccommodatingthenewPCCandstabilizedsubbase(P-304CTB)thicknesses.Followingareviewofthepavementthicknessrequiredouranalysisshowedthatthispavementsectioncouldoccurwheretheleveldifferencewasinexcessof550mm(21.75)infill.The550mmlowerlimitconsistsofnew400mm(15.75)PCCand150mm(6)P-304CTB,asdepictedinFigure3below.Forleveldifferencesgreaterthan550mm,aprofilecorrectioncoursewouldbeconstructedusingrecycledPCCorasphalticconcretesubbasematerials.Intheeventofashortfallinrecycledproducts,P-154materialwouldbeimportedfromoffsite.

Retentionofexistingsubbasecouldoccuriftheareahadsufficientthicknessofsubbasetoprovidecoveroverthesubgradeafterremovaloftheasphalticconcreteand/orPCCwearingcourses.Followingareviewofthepavementthicknessrequireditwascalculatedthatthispavementsectioncouldoccurwheretheleveldifferencewasbetween-165mm(6.5)incutand550mm(15.75)infillforexistingrigidpavements,orabove-165mm(6.5)incutforexistingflexiblepavements.The-165mmlowerlimitconsistsof485mmP-501PCC+150mmP-304CTB+600mmP-154existinggranularsubbase1,400mmexistingpavementthickness,asdepictedinFigure3below.Forleveldifferencesabove-165mmincut,aprofilecorrectioncoursewouldbeconstructedusingrecycledPCCorasphalticconcretesubbasematerials.Intheeventofashortfallinrecycledproducts,P-154granularsubbasewouldbeimportedfromoffsite.

Fulldepthreconstructioncouldoccurinareasbelow-165mm(6.5)incut,orwhereexistingbuildings,shouldersorgrassislandswerepresent.Inconsiderationoftheplasticandswellingnatureofthesubgradesoilidentifiedthroughgeotechnicalinvestigations,thepavementdesignincorporatedreplacementof900mm(3ft)ofexistingsubgradewithselectfillmaterialofCBR6%minimum,aspertheguidelinesprovidedinTable3-7ofFAAAdvisoryCircular150/5320-6E[5].


Figure3.TransitionsbetweenFullDepthReconstruction,KeepSubbaseandRubblization.

Afinalchallengeexistedinthattheexistingfuelhydrantmain(whichwastoremainoperationalthroughouttheconstruction)ranbeneaththesite.Astheoperatingfuelcompaniesprohibitedtheuseofvibratingrollersandrubblizationequipmentwithin3m(10ft)ofthepipeline,theseareasweredesignedspecificallytoprotectthepipeline.

Theproposedsurfacelevelsweremodeledinthe3-dimensionalgeometricdesignsoftwareprogram12D.Atthecompletionofthegeometricdesign,afull3-dimensionaltriangulationmodelwaspreparedofboththeexistingandproposedsurfaces,andtin-to-tindepthcontourswerepreparedtoshowtherelativedepthsbetweeneachsurface.Fromthisoutputthedesignerswereabletotracethe-165mm(6.5)cutand550mm(15.75)fillcontoursonalayoutplaninordertodeterminethepointatwhichthetypeofsubbasepreparationtransitionedfromfulldepthreconstructiontoretentionofexistingsubbasetorubblizationofexistingPCCpavements.

Thefinalstepinthedesignoptimizationprocesswastooptimizethenewterminalbuildingfloorlevelandaprongradientsinordertojudgetheeffectonpavementmaterialquantitiesandassociatedcostbenefits.Theaimofthisexercisewastoachieveabalancebetweenraisingthelevelssufficientlytomaximizetherubblizationarea,whilstlimitingthevolumeofprofilecorrectioncoursematerial.

The final areas of the various subbase treatment options achieved for the apronreconstructionarepresentedinTable8.

Table8.SubbaseTreatmentAreas.SubgradeTreatment Area(m2) Area(ft2)RubblizationofExistingPCC 535,000 5,759,000RetentionofExistingSubbase 155,000 1,668,000FullDepthReconstruction 220,000 2,368,000ConstructionoverExistingFuelLine 30,000 323,000

Total 940,000 10,118,000


CONCLUSION

ThepaperhashighlightedthecomplexityoftheapronpavementdesignandconstructionstagingatMumbaiInternationalAirport.Theoperationalconstraintsofthisprojecthaveresultedintherequirementtoconstructtheaproninaseriesofdiscreetstages,anditisimportanttorecognizetheneedtoimplementadvancedplanning,monitoringandcontroltechniquesinordertomaintaintheprojectscheduleinaverychallengingoperationalenvironment.

Withanaimtoeconomizethepavementdesignandconstructiontime,theexistingapronpavementlayershavebeenutilizedwhereverfeasible,inconsiderationoftheverticalgeometryoftheapronandstructuralrequirementforsupportingthedesignaircrafttraffic.ThedesignoptimizationapproachadoptedforthisprojectresultedinpavementsectionscomprisingofconstructionoverrubblisedPCC,constructiononexistingsubbase,andfulldepthconstruction.TheproposedconstructionofrigidpavementsoverrubblisedPCCisahighlightofthisprojectandtheperformancewillbemonitoredtoprovideforfutureguidelines.

Thedesignaircrafttrafficwasderivedonthebasisofadetailedtrafficanalysisandalsoonthebasisofthecriticalaircrafttrafficonstandscorrectedforpasstocoveragefactors.Thedesignthicknessesestablishedforboththetrafficscenarioswerefoundtobecomparable.Itisgenerallyacceptedpracticetodesignanapronbasedonthetaxilanetrafficandtoadoptthesamethicknessfortheparkingstands.Astherelativetrafficontaxilanesandstandsmayvarydependingonthenumberofstandsservicedbyaparticulartaxilane,itisrecommendedtocheckbothscenariosandtoadoptthehigherthickness.

Thisprojectisatruereflectionofhowsoundengineeringcan,intimesofeconomiccrisis,beanaidtoanairportbyprovidinginnovativesolutions,detailedanalysesandoptimizationofdesigns.Larsen&ToubrowouldliketoacknowledgethesupportoftheGVKGroup,MumbaiInternationalAirportLimited,andCH2MHILL(ProjectManagementConsultants)fortheproductionofthispaperandtheirsupportinadoptinginnovativeandnon-standarddesigns.

REFERENCES

1. InternationalCivilAviationOrganization,Annex14totheConventionofInternationalCivilAviation,FifthEdition,July2009

2. InternationalCivilAviationOrganization,AerodromeDesignManualPart1Runways,ThirdEdition,2006

3. InternationalCivilAviationOrganization,AerodromeDesignManualPart2Taxiways,ApronsandHoldingBays,FourthEdition,2005

4. InternationalCivilAviationOrganization,AerodromeDesignManualPart3Pavements,SecondEdition,Amendment21989

5. FederalAviationAdministration,AirportPavementDesignandEvaluation,AdvisoryCircularAC150/5320-6E,2009

upgrade of aircraft apron - pavement design

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