Geotechnics:thenext60years
B.SIMPSON*andF.TATSUOKA†
Theauthorsweresetthechallengeofthinkingaboutthe
´otechniquebutofgeotechni-next60years,notonlyofGe
calengineeringingeneral.Theyhaveattemptedtodothisbytalkingtocolleagues,bydreamingalittle,butmainlybytryingtoextrapolatethetrendstheyseeinsocietyandinpresent-daygeotechnicalactivity.Although
´otechniquetendstobere-theprincipalemphasisofGe
search,thisisdrivenbytherequirementsofdesignandconstruction.Hence,inlookingtothefuture,eventhefutureofresearch,likelytrendsingeotechnicalconstruc-tionactivitiesareconsideredfirst,particularlynotingtheemergingimportanceofenergyconservationandcarbondioxidereduction.Thisleadstodiscussionofthecharac-terisationofmaterialbehaviourandinvestigationoftheground,andthedevelopmentofdesignprocesses.Thefutureofdisseminationofgeotechnicalinformationisalsodiscussed.
KEYWORDS:constitutiverelations;environmentalengineering;groundimprovement;laboratorytests;numericalmodellingandanalysis;siteinvestigation;soilstabilisation
´fi,pourlesauteurs,c’e´taitdere´fle´chirsurles60Lede´esa`venir.NonseulementsurleplandeGe´otechni-anne
´otechniqueenge´ne´ral.Ceci,que,maissurceluidelage
´sdelefaireens’entretenantavecdesilssesontefforce
`gues,unpeudansunreˆve,etsurtoutenessayantcolle
d’extrapolerlestendancesqu’ilsperc¸oiventdanslasoci-´te´etdanslesactivite´sactuellesdansledomainedelae
´otechnique.Bienqu’enge´otechnique,onmettege´ne´r-ge
alementl’accentsurlarecherche,lamotivationest
´tudeetdelaconstruc-principalementlesexigencesdel’e
´quent,lorsqu’onsepenchesurl’avenir,tion.Parconse
ˆmel’avenirdelarecherche,onexamineenpremierme
´sdecon-lieulestendancesprobablesdanslesactivite
´structiongeotechnique,enrelevantnotammentl’impor-´nergieetlatancecroissantedelaconservationdel’e
´ductiondugazcarbonique.Ceciportea`desdiscussionsre
´risationducomportementdesmatie`resetsurlacaracte
´tudesdusol,etsurlede´veloppementdeme´thodesdese
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´otechnique.gationd’informationsdege
INTRODUCTION
Inthispaper,theauthorstrytolookintothefutureofgeotechnicalengineering,forthenext60years.Theterm‘geotechnicalengineering’istakentoincludeallformsofengineeringactivityintheground,andinwhichthebehav-iourofthegroundisrelevant;investigation,design,con-struction,maintenanceandrelatedresearchareallincluded.Besidessoilmechanics,othernecessaryskillsmightincludehydrogeology,geology,biology,chemistry,rockmechanics,structuralengineering,thermodynamics,andmanyothers.AspointedoutbyHenkel(1982),anoverlapofskillsisessentialtosuccessfulgeotechnicalengineering.
´otechniquetendstoAlthoughtheprincipalemphasisofGe
beresearch,thisisdrivenbytherequirementsofdesignandconstruction.Hence,inlookingtothefuture,eventhefutureofresearch,likelytrendsingeotechnicalconstructionactiv-itiesareconsideredfirst:theseleadtoconsiderationofthecharacterisationofmaterialbehaviourandinvestigationoftheground,andthenecessarydesignapproaches.
Inpreparationforthepaper,theauthorssentoutaques-tionnairetoalargenumberofcolleagues,askingquestionsabouttheirviewsofthefutureoftheindustryandofresearchdevelopments.Theauthorsareverygratefulfortheanswersreturned,whichhelpedthemtochoosetopicsforinclusion,andmadeusefulsuggestionsaboutlikelyprogress.However,theauthorsacceptresponsibilityfortheviewsexpressedinthepaper.Obviously,anyviewofthefutureisspeculativeanduncertain,butforbrevity,withnointendedpresumption,statementsaboutthefuturearemadeinasimplefuturetense,generallyomittingwordingsuchas‘theauthorsexpect(orguess)that...’.
Thepotentialscopeofthediscussionisvast,sothepaperisrestrictedtoasmallselectionoftopics.Referenceshavebeenprovidedtocurrentinformationsources,partlyinthehopethattheymaybeofhistoricinterestatsometimeinthefuture.Theauthors’overallexpectationisthatthefuturewillinvolveadvancesingeotechnology,manyofthembeyondpresent-dayimagination.Butitisacknowledgedthatitcouldalsoinvolvestagnationorevenretrogressioninbothtechnologyandsociety:allofthesehavebeenexperiencedinhumanhistory.ToquoteNielsBohr:‘Predictionisverydifficult,especiallyaboutthefuture.’
Discussiononthispapercloseson1December2008,forfurtherdetailsseep.ii.
*ArupGeotechnics,London,UK.†TokyoUniversityofScience,Japan.
GEOTECHNICALCONSTRUCTION
Theaspirationsandachievementsofsocietyhavealwaysbeencharacterisedbystronginteractionwithdevelopmentsincivilengineering.Hencedevelopednationswillcontinuetowantimprovedinfrastructure,commercialandresidentialbuildings,andhigherenvironmentalstandards.Advancescanbeexpectedinallformsofgeotechnicalconstruction,in-cludingtunnellingandfoundations.Groundimprovementandreinforcementarelikelytobeparticularlyimportant,togetherwithmoreadvancedtechniquesforutilisationofbrownfieldsites.Developmentsincomputation,measurementandcommunicationwillprovidenewopportunitiesandenhanceexistingprocesses.
NotingtherecentreportsoftheIntergovernmentalPanelonClimateChange(2007),itislikelythattheproductionanduseofenergy,limitingitseffectonproductionofharmfulgases,andmitigatingtheeffectsofclimatechangewillbedominantthemesincomingyears.Thesewillnecessitatedevelopmentofnewgeotechnicalskillsandwiderdisseminationofcurrentlyrareskills,andtheywillalsorequireaconsiderableincreaseinconventionalcivilengineeringactivity.Thistopicwillbeconsideredexten-sivelybelow.357
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GROUNDIMPROVEMENTANDSOILREINFORCEMENT
Groundimprovementtechnologyisstilldeveloping,anditsapplicationsinpracticeareexpanding,involvingsoilreinforcement,nailing,mechanicalandchemicalstabilisa-tion.Groundimprovementwillbecriticallyimportantinfuturegeotechnicalpractice,forthefollowingpurposesinparticular.
(a)Morecost-effectiveconstructionofinfrastructure,with
betterbalanceofcutandfill.Reinforcementenablesreductioninbothcuttingandfillingquantities,withconstructionmuchmoreefficientthantheuseofconventionalsteelorconcreteretainingwalls.
(b)Reductionofthetotalconstructionenergyusedand
CO(c)Cost-effective2emissions.
preventionandmitigationofnatural
disasters,includingthosebylandslides,soilerosion,flooding,heavyrainfall,orearthquakes.
(d)Cost-effectivesolutionsofenvironmentalissues,includ-ingtreatmentandrecyclingofindustrialandurbanwastes,wastedisposalinlandfill,andpreventionofgroundwaterpollution.Continuedresearchanddevelop-mentofgeosyntheticsisanticipated.
(e)Effectiveuseofindustrialby-productsanddemolition
materials,includingtheuseofcrushedconcreteandashfrompowerplantsasconstructionmaterials.Useoftheseasveryhigh-qualityfills,wellcompactedandpossiblywithsomecementadded,meritsfurtherresearch(e.g.Aqiletal.,2005).
(f)Remediationtechniquesofpollutedgroundandsoils.(g)Maintenanceandrehabilitationofconstructionsthatare
decayingorwhichwerenotconstructedtocurrentlyacceptedstandards.Comparedwithconcreteandsteelstructures,deteriorationduetoageingisgenerallylesssignificantforsoilstructuresconstructedbycompactingunboundbackfill.Soilreinforcementcanbeusedeffectivelytoprovideprotectionfornaturalslopesandtoaugmentembankments,andthismaybecomemoreimportantinfutureifclimatechangeleadstomoresevereweatherevents.Groundimprovementtechniquesareusuallyusedeithertoreducethestressesintheground,particularlytheshearstress,ortoenhancetheshearstrength.Stressesinthesoilcanbereducedbytheuseoflightweightembankments,micropilingandtensilereinforcement.Forcompactionofexistingunboundbackfill,apartfromtheconventionalcom-pactiontechnologiesdiscussedabove,newcost-effectivecompactionmethods,suchasheavytampingandunder-groundandunderwatercompaction,willbedeveloped.Chemicalmethodsofincreasingshearstrength
Itisanticipatedthatmorepermanentsoilstructures,suchasbridgeabutmentsandfilldams,willbeconstructedbyusingcement-mixedbackfill.Also,morepermanentsuper-structureswillbeconstructedonandinexistingsoilstrataimprovedbycement-mixingin-placeandembankmentscon-structedusingcement-mixedsoil.Theboundarybetweencement-mixingtechnologyingeotechnicalengineeringandconcreteengineeringwillbecomelessimportant.
Supportingthesedevelopmentsinconstructionpractice,researchwillprovidebetterunderstandingofthestress–strainpropertiesofchemicallyimprovedgeomaterialbyproperlytakingintoaccountrelevantinfluencefactorsthatarenotimportantforuntreatedgeomaterials,suchastheeffectsofageing,heatandchemicalreactions,andtheircombinedeffectsandinteractionswiththeelasto-viscoplasticproperties.Onlyoncethestrengthanddeformationcharac-
teristicsofchemicallyimprovedgeomaterialsareproperlyunderstoodandevaluatedwilltheirusetoconstructimpor-tantprimarysoilstructuresbecomestandardgeotechnicalpractice.
Tensilereinforcement
Tensilereinforcingtechnologiesinclude:(a)thoseusedtoreinforceexistinggroundandslopes(e.g.nailing);and(b)thoseusedtoreinforcebackfill,usuallybyplacingmetalstripsorgeosyntheticreinforcementlayersduringconstruc-tion.Givenconfirmedlong-termdurability,bothtypesoftensilereinforcingtechnologyarebecomingusedroutinelyinmanycountries.
Ongoingdevelopmentoftype(b)isanticipatedforuseinpermanentstructures,suchasbridgeabutments,inplaceofconventionalconcretestructuressupportedbypiles.Forexample,Tatsuokaetal.(2007)describeareinforcedcon-creteintegralbridgewithabackfilledabutmentreinforcedwithgeosynthetics.Thedesignofthistypeofstructurerequirestheintegrationofgeotechnicalengineeringandstructuralengineering,asinthefoundationdesign.
Combinedchemical–mechanicalmethods
Thetechnologiesdescribedaboveareoftenusedinisola-tionatpresent,buttheiruseincombinationcouldbeparticularlypowerful.Combinationsofmechanicallyandchemicallystabilisedgroundwillbefounduseful,suchasmechanicallystabilisedbackfillstructuresconstructedonchemicallyimprovedsoftground.Permanentsoilstructures,includingfoundations,madeofcement-mixedbackfillorexistingground,reinforcedwithsteelorfibre-reinforcedplasticrodsorgeosyntheticreinforcement,willbecomepopularinsomesituations.
DEVELOPMENTOFBROWNFIELDSITES
Overthenext60yearstherewillbeanongoingneedtodevelopexistingbrownfieldsites:thatis,previouslydevel-opedland,whichmayormaynotbecontaminated.Theincreasingamountsofelectrical,electronic,chemical,house-holdandevennuclearwastewillpresentmajorchallenges.Engineersandscientistshavebeenenablingthedevelop-mentofbrownfieldsitesforhundredsofyears,bythesimpleprocessesofdigginganddumpingelsewhere,orbybreakingthepathwayofpollution,andcoveringup.Legislationwillcontinuetogettighter,requiringinnovativeremediationsolutions,possiblyusingtransferableskillsandtechniquesfromothersciences,suchasmedicine,biochemistry,physicsandbiology.Inadditiontodevelopmentintheuseofgeosynthetics,asnotedabove,suchsolutionscouldinclude(a)moresophisticated,possibleeven‘intelligent’,per-meablereactivebarriers
(b)heattreatments,perhapsharnessingsolarpoweror
geothermalpower
(c)injectedchemicaltreatmentsthatwouldeither‘fix’
contaminantsorcreatebarriers
(d)theuseofplants,possiblybiomassfuelplants,tobe
grownoncontaminatedsitesto‘adsorb’contaminants(e)nanotechnology,suchasthenanozero-valentiron
technologies,inwhichhighlyreactivenanoironparticlescauselessreactivemetalstoprecipitateontothem(Ifpresentuncertaintiesaboutsafetycanbetackled,thistechniquemaybesuitablefortheremediationofverydeepplumesofcontaminatedgroundwater,injectingnano-sizedironparticlesdeepintothegroundthroughwells.)
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(f)betterriskassessmenttechniques,usingabetterunder-standingofthetoxicologyofisolatedandinteractingchemicals,possiblyeliminatingsomecurrentconcerns.Itispossiblethatlandfillingascurrentlypractisedwilleventuallydisappear,withimprovedtreatmenttechnologiesallowingthereuseandsharingofsurplussoils,perhapsthroughregionaltreatmentandstoragecentres.Alternatively,insteadofremediation,itmightbecomethenormtoleavecontaminationintheground,developoveritsafelybyisolatingtheenduserandtheenvironmentfromit,allowgroundwatertobecomepolluted,andremediateortreatitonlywhenitisextractedforuse.
Interpolatinglevelsofpollutionbetweenasmallnumberofscatteredsamplesmaybeverymisleading,sonewmeth-odsofinvestigation,detectionandmeasurementareneeded,combinedwithstatisticalanalysis.Weanticipatethedevelopmentofremotesensingtechniquesandofadvancedsoilprobesthatcancarryoutcontinuoussamplingandtestinginsitu.
Hopefully,societywilllearnthelessonsofthepastandavoidcreatingnewbrownfieldsites.Whateverhappens,engineerswilluseaconsiderablevarietyofsolutions,rememberingthatsometimesthesimpleonesarebest.UNDERGROUNDSPACEANDTUNNELLING
Greateruseofundergroundspaceisanticipated,bothasaccommodationandtoimprovetheefficiencyoftransporta-tion,requiringnovelandmorepowerfulconstructiontechni-ques.SomerecentdevelopmentsarediscussedbySimpson(2007a),notingthatconstructionbelowthesurfaceofthegroundoffersnotjustmorespacebuttheadvantagesofawholenewdimension.Admiraal(2006)hasrightlypointedout,however,that‘undergroundspaceisnotavirtuallylimitlessreservoirwaitingtobeexploited’.Arguingthathumanshaveanurgentneedtoexploitthespacebelowthegroundsurface,healsoadds‘butneithercanitbepreservedasanaturereserve’.
Majorexcavationsincitiesaredisruptiveandpotentiallydamaging,soitisimportanttomonitorstressesanddispla-cementsinstructuresandtheground.Wecanexpectmuchgreaterapplicationofrecentdevelopmentsintechnologies,suchasfibreoptics,wirelesscommunication,measurementfromsatellitesandtheuseofinternetdatabases,andfurtherdevelopmentswillmakethemmorecommoninthisandotheraspectsofgeotechnicalengineering.
Technicaldevelopmentsareanticipatedbothinsprayedconcretetunnellingandinshieldtunnellingtoreducegrounddeformationandprovidecost-effectiveconstruction,withautomationofexcavationandliningerection.Innovativemethodsofformingundergroundspacessuchasstationswillincludemultiple-tubetunnels,asdescribedfortheShanghaiRailTransitProjectbyChow(2006),orthemulti-microshieldtunnellingdescribedbyHirosue&Kagami(2006),atech-niquethatallowstheconstructionoflargerectangularunder-groundspacesbytunnelling,withouttheuseofcut-and-cover.ENERGYANDCARBONCONSIDERATIONS
HelpingenergyuserstoreducecarbondioxideemissionsIntheUnitedKingdom,heatingandcoolingoflivingspaceandwateraccountforabout34%ofhumanenergyusage(DepartmentofTradeandIndustry,2003).Thegeo-technicalprofession,alongwithmanyothers,isseekingwaysofmakingthisprocessmoreefficient,andthepossibi-litiesofusingthegroundasasource,oratleastasastore,ofheatandcoldshowsomepromise.Admiraal’sstatementsonthelimitationsofspacebelowground,notedabove,are
equallyapplicabletoitsuseforthermalpurposes,andabalanceofheatinputandoutputisusuallynecessary.
Forrelativelysmallbuildingssurroundedbyalargeamountofopenland,itispossibletopumpwaterinpipesthroughthegroundatshallowdepth,typicallyabout1.5mbelowthegroundsurface,inordertoexchangeheat.Con-cernsabouttheeffectofthisprocessonvegetation,includ-ing,intheextreme,freezingthegroundatshallowdepth,requirecarefulconsideration.Inprincipleitmaybepossibletousethistypeofsysteminan‘unbalanced’manner,thatis,forunequalamountsofheatingandcooling,relyingonheatinterchangewiththeatmospheretomakeupthedifference.Thisrequires,inparticular,greaterunderstandingofthethermalandhydraulicpropertiesofthelayersofsoilclosetothegroundsurface,whicharegenerallyunsaturated.Manyauthors(e.g.Brandl,2006;Law&Nicholson,2006;Hofinger&Adam,2007)havediscussedsystemsforinterchangeofheatwiththegroundatdepth,usingeitherwellsorconductionthroughconcreteelementssuchaspilesandretainingwalls.Theyhavegenerallyshownthat,inmostcasesinvolvinglargebuildings,thegroundcanbeusedonlyasatemporarystoreofheatorcooling,oneitheranannualoradailybasis.Onlyinrarecaseswherethereisasignifi-cantflowofwaterthroughtheground,andnoenvironmentalrestrictionspreventingwateratamodifiedtemperatureflow-ingfromthesite,canheatbetakenfromortransmittedintothegroundwithoutaneedforlong-termbalancing.
Transferofheatorcoldintothegroundisusuallybyflowoffluidfromtheaffectedstructure,eithertostructuralelementswithlargesurfaceareasincontactwiththeground,suchasfoundationslabs,pilesorretainingwalls,orbydirectflowofthefluid,inthiscasewater,intoandoutoftheground.Inthelattercase,flowmaybethroughthematrixofasoilorthroughthejointsofarock.Thereisaclearoverlapherebetweenthedisciplinesofsoilmechanics,rockmechanicsandhydrogeology,andcombinationsofexpertiseinallthreewillbeneeded.
Whereitisnotpossibleforonestructureorinstallationtousetheheatitproduceswithintheannualcycle,theheatcouldpotentiallybesharedwithotherusers.Forexample,intheUnitedKingdom,manylargebuildingscurrentlyproduceexcessheatoverthewholeyear,butmostdomestichomesdonothaveairconditioninganduseenergyonlyforheating.Onesolutioncouldbetore-planmuchoftheurbanareas,andbeyond,soastobringproducersandusersofheatnearereachother(e.g.Ward,2008).Reorganisationofthebuiltenvironmentonsuchascalewouldinevitablyleadtoamassiveamountofcivilengineeringconstruction,includingthenecessarygeotechnicalengineering.Whilemuchofthiswouldbeconventionalinnature,economyintheuseofenergyandincarbondioxideemissionswouldbeveryimportant,asdiscussedfurtherbelow.
Somesimpleopportunitiestotakeheatfromproducerstousersmayalreadyexist,andcouldbegeotechnicalinnature.Forexample,thepossibilityhasbeendiscussedofcoolingundergroundraillinesbyconductingtheheatintotheground,andlaterextractingitfordomesticheatinginhomesclosetotheundergroundlines.Itcouldbetakenouttohomesonthesurfaceabovebywatercirculatinginpilesorwells.Hofinger&Adams(2007)describetheheatingofaschoolinthisway,andmentionslabs,piles,tunnelliningsandalsogroundanchorsasdevicesthatcanbeusedtotransmitheatintotheground.
Thisbriefreviewofwaysinwhichgeotechnicalengineer-ingmighthelpsocietytoreducecarbondioxideemissionsshowsthatgeotechnicalengineerswillneedtodevelopabetterunderstandingofthethermalbehaviouroftheground,intermsofbothitscapacitytotransmitandretainheat,andtheeffectsoftemperaturechangeonotherpropertiessuch
360SIMPSONANDTATSUOKA
asstrength,stiffnessandsolubilityofsolidcomponentsingroundwater.Unsaturatedsoilmechanicsandbiologicalissuesmayalsoberelevant,andhydrogeologywillbeveryimportant.Itisunlikelythatsingleindividualswillbefullycompetentinallthesedisciplines,butengineersmightdevelopcompetenceinvariouscombinationsofthem,andeducationcoursescouldalsocombinetheminsomeway.Todate,mostofthepublisheddataonheatinterchangewiththegroundrelatetotrialsratherthantofull-scaleconstructions,andafullexplanationofthescienceisrarely
provided.ItisthereforeverytimelythatGe
´otechniquewillholdaSymposiuminPrintin2009onthesubject‘Applica-tionsaffectedbythethermalcharacteristicsoftheground’.Reducingenergyusageandcarbondioxideemissionsinconstruction
Theprocessofcivilengineeringconstructionisamajoruserofenergyinitsownright,soitwillbeimportanttoreducethiswhereverpossible.Itisanticipatedthatstudiesofthewhole-lifeenergyusageofprojectswillbecomemorecommon,requiringcomparativeassessmentoftheembodiedenergyinconstructionmaterials,energyusagetoformaconstruction,andenergyrequiredduringtheoperationallifeofastructure.
Forexample,Chauetal.(2006)haverecentlystudiedtheembodiedenergiesofvarioustypesofembeddedretainingwall.Theynotethatthemanufactureofbothsteelandcementconsumesalotofenergy,andtheyconcludethatsteelwalls,usingrecycledsteel,havemuchlessembodiedenergythanconcretewallsofsimilarstiffness.However,theuseofvirginsteel,nowcomparativelyrareinEuropeanconstruction,entailsmuchmoreembodiedenergy.
Reducingembodiedenergyinconstructionwillleadtogreaterreuseofmaterials,theuseofpoorer,butlocallyavailable,fillmaterials,andgreateruseofmanyformsofgroundimprovement.ReuseofpiledfoundationshasbeenstudiedatsomelengthintheRUFUSproject(Chapmanetal.,2004),andconsiderationsoftheuseoffillandstructuralmaterialsinconstructiononsoftgroundarediscussedbyO’Riordan(2007)onthebasisofitsimportancetothedesignoftheChannelTunnelRailLinkintheUK.
Theauthorsanticipatethatpractisinggeotechnicalengi-neerswillneedtobecomeproficientinassessingtheenergyrequirementsofconstruction,andthiswillalsobeanimportantaspectofresearchincomingyears.
Alternativesourcesofenergy
Formanyyears,geotechnicalengineersandgeologistshavebeencriticallyinvolvedintheextractionofcoal,oilandgasonlandandsea,andintherelatedinfrastructure.Itisanticipatedthatthiswillcontinue,perhapswithrenewedemphasisoncoalasoilandgaspotentiallybecomemorescarce.Interactionsbetweenminingengineering,geology,rockmechanicsandsoilmechanicswillbeessential.If,asseemslikely,itisnecessarytoextractoilandgasfromdepletedormarginalfields,betterunderstandingofthegeomechanicsofoilandgasreservoirswillbeimportant.Forexample,problemssuchas‘sanding’duetooverstressingofsandstonewillrequiremoreinvestigationtogiveabetterunderstandingoftherockandsoilmechanicsinvolvedinthecrushingofthematerial.Workonthisisalreadyunder-wayatvariousresearchcentres.
Ifoilandgasstarttobecomemorescarce,coalwillprobablygrowinimportanceasaprimarysourceofenergy.InChina,forexample,thereiscurrentlyarapidexpansionindeepcoalmining,withminestypicallyextendingtodepthsexceeding1km.Elsewhere,opencastworkingrequiresthe
formationofdeepquarries,withtheattendantproblemsofslopestabilityandwatercontrol.Althoughtheseformsofminingaregenerallyseenassomewhatspecialist,theyrequirethebasicdisciplinesofsoilmechanicsand,especially,rockmechanics,andtheparticularskillsofcombiningtheory,analysis,observationandprecedentthatcharacteriseallformsofgeotechnicalengineering.Again,therearemanypotentialopportunitiesforacademicinvolvement.
Associetytriestoreduceitsdependenceoncarbonfuels,andlooksforalternativesourcesofenergy,newgeotechnicalchallengesarise:wind,tideandnuclearenergyareconsid-eredhere.
Itislikelythatverylargenumbersofwindturbineswillbeconstructedinthecomingyears,bothonshoreandoffshore.Manyofthesemayrequirerelativelyconventionalpiledfoundations,butthesheernumberofthemarguesforcarefulreviewofthedesignprocesstooptimisethebalanceofrobustnessandeconomy.Largeroffshoreturbineswillprob-ablyusesuctionfoundations,whicharesubjecttocontinuingresearchanddevelopment(e.g.Houlsby&Byrne,2005).
Harnessingtidalpowerisachallengeoftenconsidered,butrealisedonasignificantscaleonlyintheschemeatLaRance,France,whichproducesabout100MWofpoweronaverage(EDF,2007).ThisistheonlytidalpowerschemeinEurope,andthelargestintheworld.TheSustainableDevelopmentCommission(2007)hasreportedthattheUKhasthepotentialtousetidalpowerasoneofitsmajorenergyresources,particularlyintheSevernEstuary,pro-videdtheenvironmental,socialandeconomicalimpactscanbemitigated.Anydevelopmentoftidalpowerrequirestheconstructionofverylargebarrages,probablyearthdams,whichhasbeenuncommoninmuchoftheworldinthelastfewdecades.Itseemsunlikelythatmanysuchschemeswillbebuilt,sotheirimpactonthegeotechnicalindustryasawholemaybefairlysmall.However,somerevitalisingofexpertisewillbeneeded,andsuchlargeprojectscouldwellspawnresearchopportunities.
Aresurgenceofconstructionfornuclearpowerseemslikely.Apartfromfoundationsforveryheavyloads,thisleadstotheneed,whichinfactalreadyexists,fordeepdisposalofnuclearwaste,anissuewithmanygeotechnicalaspectsandthefocusofconsiderablecurrentresearch.Suitablestrataofrelativelyimpermeablerockorclayhavetobelocatedandtested,requiringlargeinvestigations.Geologi-calstabilityisparticularlyimportant,giventhatthereposi-torymayhavetoremainsafeformuchlongerthantheageofourpresentcivilisation.Thebehaviourofthematerialandwaterinporesorfissuresastemperaturechangeshastobeunderstood,togetherwiththegroutsandclaysusedtosurroundandcontaintheradioactivewaste;someofthismaterialwillinitiallybeunsaturated.Assomeradionuclideswillinevitablyescapetheirimmediatecontainment,theiradsorptionontotheparticlesurfacesofsurroundingmaterialswillbeimportant,aswillafullunderstandingoftheirmove-mentthroughthematerialsingroundwater.Geotechnicalengineeringandnuclearengineeringwillclearlyoverlapin
thesestudies;theGe
´otechniqueSymposiuminPrintof2007containsseveralrelevantpapers(Bernieretal.,2007;Delageetal.,2007;Gensetal.,2007;Piriyakuletal.,2007).GeotechnicalengineeringwillalsocontributetothesaferconstructionofnuclearpowerplantsinhighlyseismiczonessuchasJapanbymorereliablepredictionoftheinputmotiontothestructuresandtheseismicstabilityofthesupportingground,andbythedesignoffoundationstructures.
Mitigatingeffectsofclimatechange
Potentialeffectsofclimatechangevaryaroundtheworld,includingrisingsealevel,moresevererainfallevents,and
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hotter,drierconditions.Needsforneworrenewedstructuresforseaandriverdefencecanbeexpected.Verymajorconstructionsmightbeneeded,possiblyfundedonaglobalbasis,iflargeareasoflow-lying,populatedlandarenottobelost.Suchstructures,forexampleonthescaleoftheOosterscheldeBarrier,completedintheNetherlandsin1996,naturallyleadtomajoradvancesinsoiltestingandresearch,andalsoinconstructiontechnology.
Thestabilityofbothexistingandnewslopes,cuttingsandembankmentscouldbechallengedbyheavierrainfall,re-quiringreassessmentandmodification.Similarly,foundationdesignscouldbeaffectedbyhigherormorevariablewatertables,orbymoreseverecyclesofdryingandwetting,especiallyinshrinkableclays.Currentresearchinunsatu-ratedsoils,andintotheeffectsofcyclesofsaturationanddesaturation,willbeimportant,andmorewillbeneeded,incombinationwithfieldstudies,tounderstandandcontrolthisdifficultareaofgroundbehaviour.
Gashydrates
Methanegashydratesaresolid,ice-likecompoundsformedfromhydrogen-bondedcagesofwatermoleculesenclosingmethanemolecules,whichcanleadtolargevolumesofmethanegasbeingstoredwithintheirstructure(Sloan,1998).Thesecompoundsarewidespreadinthetopfewhundredmetresofsedimentbeneathcontinentalmarginsinwaterdepthsgreaterthanafewhundredmetres(owingtothetemperatureandpressurerestrictionsunderwhichhy-dratesform).Thishasledtogashydratesbeingofinterna-tionalimportancewithregardtothefollowing.
(a)Thepotentialtobeafutureenergyresource:1m3of
hydrateisequivalentto164m3ofmethanegasatstandardtemperatureandpressure.Theestimatedglobalvolumeof3methanestoredinhydraterangesfrom2to431016matstandardtemperatureandpressure(Kvenvolden,1988,1998;McDonald,1990),whichistwicethetotalreservesofhydrocarbonenergyfromallotherfossilfuels.ExplorationwithaviewtothedevelopmentofhydratereservesiscurrentlyunderwayinIndia,China,Japan,MalaysiaandKorea.Geotech-nicalengineerswillplayanimportantroleinthisdevelopment.
(b)Theirroleinglobalwarming:methanegasthatis
containedingashydratesis20timesmorepotentasagreenhousegasthancarbondioxide.Ithasbeenpostulatedthathydratedissociationandthereleaseofmethanegasintotheatmospherewouldsignificantlyincreaseglobalwarming.Hydratedissociationmayhavebeenthecauseofsomeofthemassextinctionsinthegeologicalpast(Haq,1998).Geophysicists,supportedbygeotechnicalengineers,areplayingakeyroleindevelopingmoreeffectivewaysofdetectinghydrates.(c)Thepossibilityofbeingageotechnicalhazard:upon
dissociation,ice-likegashydrateconvertsbacktoitsindividualcomponentsofgasandwater.Thiscanleadtoareductioninstrengthofthesedimentalongwithachangeinstressconditionsduetotheover-pressurisa-tioncausedbythereleaseofmethanegas.Thishasbeenlinkedtolarge-scaleslopefailuresoncontinentalmarginsthathaveoccurredinthegeologicalpast(Kayen&Lee,1991;Popenoeetal.,1993;Meinertetal.,1998;Ashi,1999;Berndtetal.,2002).Onasmallerscale,offshoreoperatorsareincreasinglywork-ingonpotentiallyhydrate-bearingsedimentsoncon-tinentalslopes(e.g.theOrmenLangedevelopmentoffNorway).Itisfearedthatdrillingactivitiesmightbecapableofdissociatinggashydrates,givingrisetooil
platformblowouts,casingfailuresand,attheextreme,platformsubsidence(Bily&Dick,1974;Franklin,1980).Geotechnicalengineersareinvolvedintestingtoexaminetheeffectsofdissociationonthepropertiesofhydrate-bearingsediment,andinmodellingtheseeffects(e.g.bydevelopingcoupledthermo-chemo-mechanicalnumericalelementmodelling).
Thechallengesofdeterminingthethermo-chemo-mech-anicalproperties,throughinsituandlaboratorytestingofsedimentsfoundatwaterdepthsofthousandsofmetres,andthenmodellingtheimpactsofhydratemining,globalwarm-ing,andhydrocarbonexploitation,areenormous,andareincreasinglyinvolvinggeomechanicsresearchers(e.g.Claytonetal.,2005;Priestetal.,2005;Sogaetal.,2007).
SOILMODELLING
Thedevelopmentofstress–strainmodelsforsoils,mainlyforuseinfiniteelementanalysis,hasbeenamajorfeatureofresearchoverthelast60years.Inpractice,thecommonlyusedmodelsarerelativelysimple:elasticMohr–Coulombmodels,modifiedCam-clay(Roscoe&Burland,1968)andsmallextensionsofit,anddevelopmentsofthehyperbolicmodelsofDuncan&Chang(1970).AfewmorecomplexmodelsareinregularuseintheUK(e.g.Jardineetal.,1986;Simpson,1992),butmostmodelsdevelopedinre-searcharerarelyused,perhapsbecausetheyrequiremanyparametersthataredifficulttoevaluate.
The2007Ge
´otechniqueSymposiuminPrintservedtoillustratetheverygreatcomplexityofrealsoilbehaviour(e.g.Simpson,2008),andthoughitsrelevancetopracticalproblemswasapparent,therewasstillacleargulfbetweenwhatcouldbeunderstoodinprincipleandwhatcouldbeappliedinpractice.Notonlythedeformationpropertiesbutalsothestrengthofsoilsarepoorlymodelledinengineeringpractice(Hightetal.,2007).Tatsuokaetal.(1991,1997)andSiddiqueeetal.(1999)havepointedoutthatfailuretoconsidertheeffectsofdeposition,progressivefailureandothereffectsindensesoilscanleadtolargeoverestimatesofavailableshearstrength,whilefailuretorecognisetheeffectsofgrainsizeortousethebenefitsofgoodcompactionmayleadtounderestimates.
Furtherresearchisanticipated,mainlybyacademics,tocapturethestress–strainbehaviourofsoilmoreaccuratelyinordertodevelopmorerealisticmodels.Theaimsofthedevelopmentwillinclude
(a)moredetailedunderstandingofstress–strainand
hydraulicbehaviour
(b)moregeneralunifiedmodels
(c)modellingofsoilparticlesandinterparticlecontactsfor
numericalmethodsthatcandirectlysimulatetheparticulatenatureofsoil(e.g.thediscreteelementmethod,DEM).Forthepurposesofpracticaldesign,simplemodelswillcontinuetobeapplied,butthesewillbemostusefulandreliablewhentheuserisinformedbythebestpossibleunderstandingofrealbehaviour.Technologytransferfromresearchtopracticewillremainimportant,thoughoftendifficulttoachieve.
Moredetailedunderstandingofbehaviour
Thedeformationpropertiesofgeomaterialsaredifferentfromthoseofmostman-madematerialsinseveralimportantrespects.
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(a)Theirbehaviourisessentiallyfrictional,withorwithout
interparticlebonding.
(b)Theydisplayanextremelywiderangeofstrengthsand
stiffnesses.
(c)Theirpropertiesarenon-constant:theyreadilychange,
controlledbysuchfactorsasdensity,confiningpressure,stresshistory,rateeffects,andageingeffects.(d)Theirpropertiesarecomplex,with,forexample,
extremelyhighstrainandstressnon-linearity,largeeffectsofstresshistory,dilatancy,anisotropy,andstrain-softeningassociatedwithshearbanding.Becauseoftheinherentlydifficultnatureofgeomaterials,theircharacterisationandmodellinghavedevelopedfromsimplifiedpictures—essentiallyslipsurfaceorcontinuummodels—usedintheearlystagesofgeotechnicalengineer-ing.
Theclassicalgeomechanicstheoriesofearthpressure,bearingcapacityandslopestabilityprovideasimpleillustra-tionofthispoint.Althoughbasedondifferentmathematicalmethods(upper-orlower-boundtypesorlimit-equilibriumtypes)anddifferentfailuremechanisms,mostofthemassumeisotropic,perfectlyplasticsoilpropertieswithzero-thicknessshearbands(i.e.shearsurfaces).Thissimplifiedclassicalsoilmodelignoresnotonlypre-peaknon-linearstress–strainbehaviourbutalsoanisotropy,andstrain-soft-eningwithshearbandshavingathicknessproportionaltoparticlesize(e.g.Finnoetal.,1997;Okuyamaetal.,2003).Becauseofthis,realisticpredictionofgrounddeformationandstructuraldisplacementsbyclassicalsoilmodelsisnotpossible(e.g.Siddiqueeetal.,1999),andcontinuedresearchwillbeneededtoincludeawiderrangeoffeatures.Mathe-maticalconsistencyorcorrectnessalone,oftensoughtinacademicgeotechnicalstudies,arenotsufficient.
Moreaccurateandreliablepredictionofdisplacementsduringconstruction,inthelongterm,andduetoloadingsuchasearthquakeswillcontinuetobechallenging.Presenttrendsinthepredictionofdisplacementsaremoving(a)towardscomplexnon-linearanalysis(b)towardselasto-viscoplasticanalysis
(c)towardstheinclusionofcyclicloading,chemical
effects,ageingeffectsandthermaleffects
(d)towardsincreasedconsiderationofcouplingeffects
amongtheseeffects(probablyimportant,butlittleunderstoodatpresent)
(e)towardsmoredevelopmentsinunsaturatedsoilmech-anics.Capabilitiesforthepredictionoftime-dependentgrounddeformationandresidualstructuredisplacementsduringlong-termservicearestillverypoor.Forexample,topredictthesecondaryconsolidationofclay,bothviscousandageingeffects,interactingwithyieldingproperties,shouldbetakenintoaccount.Althoughtheeffectsofageingcanbeevalu-atedtosomeextent,ourunderstandingoftheactualprocessofageing(usuallybychemicalandthermaleffects)isverypoor.Thisrelatestobothengineeringandgeologicaltime-scales,andiscoupledwithyielding,viscousandthermaleffects.
Untilquiterecently,mostsoilmodellingwasforsaturatedsoilsordry,coarse-grainedmaterials.Thebehaviourofpartiallysaturatedsoilsisnowattractingmuchattention,stimulatedbyconstructionindrierregions,theimportanceoffillmaterialsinmostregions,andgrowinginterestinconditionsaroundproposeddeeprepositoriesfornuclearwaste(e.g.Gensetal.,2007).Althoughthisseemstobeonemorecomplexfeaturetoaddtosoilbehaviour,itislikelythatreasonableapproximationstothebehaviourcanbeachievedwithoutunduecomplexity.Climatechangeand
theneedfornuclearpowerarelikelytodrivethistopicforwardinthecomingdecades.
Futureactivitiesinthedeepseaandonotherplanetsmayneednewframeworksoftheorytoincludetheeffectsofveryhighporewaterpressure,ofstress–strainbehaviouratverylowpressureandatverylowandhightemperatures,andofporefluidsotherthanwater.Itwillbecomenecessarytodecidetheextenttowhichcurrentideascanbeextendedtothesenewconditions.
Moregeneralunifiedmodels
Toachieveoriginality,researcherstendtospecialiseinnarrowtopics.Forexample:
(a)Researchersspecialisingeitherinsaturatedsoftclayor
inunboundgranularmaterialsdevelopdifferentcon-stitutivetheoriesandmodels.
(b)Researchersspecialisinginsoilmechanicsandrock
mechanicsdealdifferentlywithdiscontinuitiesandheterogeneitiesinagivengeomaterialmass.
(c)Geotechnicalresearchersquantifythephysicalproper-tiesofagivenstratum,whereasgeologistsdescribequalitativelythewholestructureofagivenstratum.Ontheotherhand,ingeotechnicalengineeringpracticeengineershavetodealwithawidevarietyofgeomaterials,requiringnotonlythedetailedbehaviourofindividualspeci-mensbutalsoaqualitativedescriptionofthewholestructureofagivenstratum.Increasedeffortstodeveloptheoriescoveringdifferenttypesofgeomaterial(boundandunbound,fromsoftclays,sandsandgravelstorocks,saturatedandunsaturated)wouldbeverybeneficial,sincemanyrealgeomaterialsfallbetweenthevarioustypes.Nevertheless,itwouldbeamistaketoloseimportantaspectsofthemodel-lingofonematerialbytryingtomakeitfitamoregeneralframework.Inparallel,effortstomergesoilmechanicsandrockmechanicsaswellasgeotechnicalengineeringandappliedgeologymaybecomemorerelevantandthereforebepursued,firstinpractice,thenineducation,andtheninresearchandinlearnedsocieties.
Modellingsoilparticlesandinterparticlecontacts:theDEMAlthoughsoilisaparticulatematerial,thisnatureisusuallynotdirectlytakenintoaccountinsoilmodelling.Recently,thediscreteelementmethod(DEM)hasbecomepopularbecauseitcancapturethebehaviourofparticulatematerialsbetterthanthefiniteelementmethod(FEM).
ManyrespondentstothequestionnairesentoutbytheauthorssuggestedthattheDEMwouldbeaprominentfeatureofdevelopmentsinanalysis.Analysestodatehavebeenlimitedtoabout105particles,generallycircular(2D)orspherical(3D),butonerespondentsuggestedthatcomput-ingpowerandtheuseofparallelprocessingwillallowanalysesof106oreven109particles.Cundall(2001)hassuggestedthat1011particlescouldbeavailablewithin20years.Althoughthese3numbersseemimpressive,itisob-servedthatin1mthereare106cm3and109mm3,sorealsoilswouldhaveconsiderablylargernumbersofparticlespercubicmetre,eachparticlebeingcomplexinshape.Hencetheprospectofmodellingmostrealboundaryvalueproblemsonaparticle-by-particlebasisseemsremote.Itmightbepossibletomodelpracticalsituationsusingmuchlargerparticlesprovidedanappropriatescalinglawisadopted,assuggestedforaslopestabilityproblembyCundall(2001),butsituationsinvolvingstrainlocalisationintoshearbandsandporewaterflowinnarrowbandswillbeparticularlydifficult.
TheDEMhasbeenusedasa‘computerlaboratory’to
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simulatedirectsheartestsortriaxialtests(e.g.Cuietal.,2007;Zhang&Thornton,2007)andtoinvestigatesoilliquefaction(ElShamy&Zeghal,2005),anditcouldhaveotherimportantapplicationsinmorefundamentalwork.Forexample,ithasbeenusedinstudiesoftherelationshipsofinterparticlefriction,rollinganddilationtotheangleofshearingresistanceö9(Thornton,2000),andinstudiesofthesignificanceofparticlecrushinginexplainingthefamil-iarlog-linearcompressionbehaviourofsoils(e.g.McDowell,2002;Chengetal.,2004).Otherfeaturesofsoilbehaviour,includinganisotropyofstrengthandstiffness,andcreep,mightalsobestudiedinthisway.
TheDEMneedssoilpropertycharacterisationsthataretotallydifferentfromthoserequiredforcurrentlyusedgeomaterialmodels.FormorerealisticsimulationsbyDEManalysesofthestress–strainbehaviourofgeomaterialfromsmallstrainstowardsresidualstate(andalsoflowbehaviour)inresearchandpractice,developmentofthefollowingaspectsisanticipated
(a)simulationsoftheeffectsofparticleshape,stiffness,
strength,crushability,etc.
(b)amorerealisticdescriptionofinterparticlecontacts
(elasto-viscoplastic,withandwithoutbonding)
(c)asignificantincreaseintheparticlenumbersthatcan
besimulated,sothatshearbandinginalargesoilmassasencounteredinfieldboundaryvalueproblemscanbecaptured,and3Dsimulationsbecomefeasible.Eventhen,forpracticalapplication,calibrationofthemodelbylaboratorystress–straintestsand/orfull-scalefieldmonitoringwillalwaysbenecessary.TheessenceoftheDEMistorecognisetheparticulatenatureofsoils,incontrasttothebasicassumptionsofcontinuummechanics.Evenifthisformofcomputationdoesnotprovetobeviable,itislikelythatcomputationsthatmodelthenon-continuousnatureofsoils,withdiscreteloadpaths,fracturesandsimilarfeatures,willbecomeimportantandmightprovideamajorstepforward.Aparadigmshiftinthinkingmaybeneededtoapplytheresultsinpracticalengineering.
Reducingthegapbetweenresearchandpractice
Thereareseveralreasonsforthecontinuinguseofclassicalsoilmechanicsinpractice,includingthefollowing.(a)Itisstillverydifficulttocapturethecomplete,accurate
pictureofagivensoilstratuminthefieldwithsufficientdatatorepresenttheimportantfeaturesdiscussedabove.Thisisbecauseofinherenthetero-geneityduetothecomplicatedhistoriesofdepositionandloadingofsoilstrata.
(b)Thebestavailablesoilmodelsareusuallyhighly
complex,withmanyparametersnoteasilydetermined.Theanalysesmaybeverycostly,thoughnotveryreliable,dependingcriticallyonsmallvariationsinsomeparameters.Atpresent,thegapbetweentheacademicsoilmodelsandthoseusedindesignisincreasing,except,perhaps,inthedesignofspeciallargeprojects.Itisoftenimpracticalforadesignertodevelopafullunderstandingofacomplexmodel,whichmightcontainmanyfeaturesnotrelevanttotheprobleminhand.Thedevelopmentofsimpler,morerobustmodelsthatreproducefeaturesrelevanttoalimited,butclearlydelineated,rangeofsituationswillthereforeremainimportant.
InJapan,becauseoftheveryhighdesignseismicloadsusedinthedesignofinfrastructurefollowingthe1995KobeEarthquake,ithasbecomenecessarytousethepeak
strengthaswellastheresidualstrength,ratherthanadesignshearstrengththatpreviouslyhadbeenessentiallythesameastheresidualshearstrength.Possibleeffectsofparticlesizearealsotakenintoaccountifnecessary.Initialexamplesofthisapproachinclude(a)modifiedMononobe–Okabedynamicearthpressure
theory(Kosekietal.,1998)
(b)modifiedNewmarkmethodtoevaluateseismicslip
displacements(Okuyamaetal.,2003)
(c)limitequilibriumanalysisusingresidualstrengthto
obtainthesafetyfactorforthecriticalfailureplanethatissoughtinadvancebylimitequilibriumanalysisusingpeakstrength(Tatsuokaetal.,1998:Leshchinsky,2000).NewJapaneserailwaydesigncodesincorporatepartoftheabove(RailwayTechnicalResearchInstitute,1999,2007;Kosekietal.,2008).
GEOTECHNICALINVESTIGATIONS
Informationcurrentlyavailablefordesignisofteninsuffi-cienttoproviderealconfidenceandeconomy,especiallyinthecaseofexistingstructuresfacingnewthreatssuchasnaturaldisasters.Moreover,standardsofdesign,constructionandmaintenancewillcontinuetodevelop,requiringnewdatasetsofgroundinformation.
Thedevelopmentofcost-effectivesiteinvestigationwillcontinue,withtheaimofcapturingtheoverall,detailedandaccuratepropertiesofagivensoilstratum.Thiswillentailintroducingnewtestmethods,andimprovementsinsoft-ware,hardwareanddatainterpretation.
Insitutesting
Geotechnicalfieldinvestigationwillalwaysbeimportant,anddevelopmentstobeexpectedincludethosenotedbelow.(a)Theuseofexistingsoundingtechnologies,including
theSPT,conepenetrometers,pressuremetersanddilatometers,willcontinue.Bettercorrelationsbetweentheiroutputsandgeomaterialbehaviourwillcontinuetobesought,basedonthelatestgeomechanicsknowledgeandinformation.Forexample,mostoftheexistingempiricalcorrelationsdonottakeintoaccountanisotropy,strainandpressurelevelnon-linearity,ortheeffectsofstressorstrainhistories.
(b)Morecost-effective,yetreliablyaccuratedirectevalua-tionsofsoilproperties(e.g.stiffnessvaluesatdifferentstrainlevelsandshearstrength).Inthisrespect,moredevelopmentanduseofnon-destructiveinsitutesting(e.g.geophysicalmethods)canbeexpected,includingremotesensingtechniquestocapturetheelasticpropertiesinanareamuchwiderorinalargergeotechnicalmassthantheselectedpointswheresoundingsareperformed.Soundingmethodsandnon-destructivemethodsevaluatedifferentpartsofthestress–strainrange,sothesetwogroupsarecomple-mentary.
(c)Muchfasterfieldloadingtests,suchasthefalling
weightdeflection(FWD)testandmethodsbasedoncompactionmachinedynamics,willbecomepopularforreal-timefaston-sitecompactioncontrolofbackfill.Thistypeofloadingtestisneededtoimprovethecurrentcompactioncontrolbasedontheapparentdegreeofcompactionmeasuredatarelativelysmallnumberofpoints.
(d)Reliableandcost-effectivefieldinvestigationsinvery
deepoffshoresituationswillberequiredrelatedto
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naturalresourceexploration.InvestigationsinsituationsofveryhighorlowpressuresmayevenextendtoplanetsotherthantheEarth,includingtheMoonandMars.
Fieldmonitoring
Morecost-effective,accurate,reliable,robust(long-term)monitoringandmeasuringsystemswillregisternotonlyconventionalgeotechnicalparameters,butalsonewcompo-nents,suchaschemical,biologicalandnuclear.Opticalfibreswillbewidelyusedtomonitordisplacementandstrain,andsatellitephotographywillbecomemorereliableandpopulartomonitorgroundsurfacedisplacementsaccu-ratelyoverlargeareas.‘Smart’structuresmonitoredusingwirelesselectronicpick-upsduringconstructionandthroughthelifeoftheprojectwillbecomerealistic,monitoringbothgroundandstructures.Improvedmeasurementswillmakeobservationalmethodsmorereliableandpopular;itcouldbethateverypassivemember,suchasatie,nail,strutorgroundreinforcement,willreportitsstateofloadingandwarnofoverloads,allowingreductionsindesignfactorsofsafety.Thesedevelopmentsalsowillbeimportantinpre-ventinggeotechnicalfailuresrelatedtoearthquakes,land-slidesetc.
Sampling
Inthelast60yearstherehavebeenverysignificantadvancesinthequalityofsoilsamplingavailable.However,eventhebestsamplesarestilldisturbed,anditmaybeimpossibletoretainsubtlemicrostructure,accuratelyreflect-ingtheeffectsofageingorrecentstressorstrainhistory.Furtherimprovementsinsamplingwouldbeveryvaluable,buttheauthorsarenotawareofanylikelyfuturedevelop-mentsthatpromisemajorgains.
Laboratorytesting
Furtherdevelopmentsareexpectedinthefollowing(a)moreautomationinoperation,dataacquisitionand
controlofstressorstrain,orboth
(b)moreflexibilityincontrolofthestressandstrainpaths
(i.e.thethreeprincipalstressesandtheirdirection;porewaterandairpressures;andthethreeprincipalstrainratesandtheirdirections)aswellasloadinghistoriesintermsofstress,stain,strainrate(monotonic,sustained,cyclicandsoon)
(c)moreaccuratecontrolandmeasurementsofstressesand
strains(e.g.averagevaluesaswellaslocalvaluesinsideaspecimenaswellasinsideandoutsideshearbands)
(d)reducedcostintheproduction,maintenanceand
operationofthetestequipmentsothatthedevelop-mentsdescribedabovecanbeenjoyedinasmanylaboratoriesaspossible.Toachievetheabove,innovationsinbothhardwareandsoftware(relevanttestprogramme,testexecutionanddataanalysisandinterpretation)arenecessary.
Foracademics,itwillnecessarytoreviewthebasicassumptionsofconstitutivetheories,andthiswillbecomefeasibleaftermoreofthedevelopmentsdescribedabovearemade.Forengineeringpractice,onthepremisethatmean-ingfullyundisturbedsamplesbecomeavailableandsignifi-cantdevelopmentsaremadeinlaboratorytesting,betterdatawillbeavailablefromtestssimulatingtypicalfieldstressandstrainpathsandpre-loadinghistory(creepetc.).How-ever,tobepracticallyusefulandrepresentative,largeseries
oftestswillgenerallyberequired,andthetestingperiodwillprobablybetoolongfortypicaldesignprogrammes.Hencetheresultsofhigh-qualitytestseriescarriedoutbyuniversitiesforacademicpurposesorinrelationtoexcep-tional,largeprojectswillcontinuetobeimportanttoengineeringpractice.
Eventhoughnewfeaturesofmaterialbehaviourarestillbeingidentifiedinlaboratorytests,laboratorytestingofgeomaterialsisbecominglesspopularthannumericalanaly-sis.Thisrecenttrendisduetotheobviousapplicabilityoftheresultsofnumericalanalyses,whethertheyarerightorwrong,andtheirapparentcost-effectiveness.Torestoreabetterbalancebetweentestingandcomputing,itishopedthatthegeotechnicalcommunitywillstrivetoachieve(a)asignificantreductioninthecostoflaboratorytesting
ofgeomaterials
(b)thedevelopmentofdesignmethodsthatusemore
realisticsoilpropertiesthatcanbeobtainedreadilyfromlaboratorytests
(c)thepopularuseoftheseteststoreducethetotal
constructioncost(orthetotallifetimecost).
Physicalmodeltesting
Centrifugetestingisnowwellestablishedasameanstosimulateagivenprototypestressstate,anditsusewillcontinueasameansofstudyingmechanismsofbehaviour.Thetestingmethodhasdevelopedwithtimeintermsofdataaccuracy,modelscaleandapplicableloadinghistory(includ-ingstageconstruction,monotonicandcyclicloading).Furtherimprovementscanbeexpected,suchasbettermod-ellingofconstructionsequences,geotechnicalprocesses,andinclusionssuchasgeosyntheticsandpiles.However,itisnotcertainwhethercentrifugetestingwilleverbeabletotackleissuessuchasviscousbehaviourandageing,andissuesofparticlesizeremainproblematic.
Databases
Inmanylocations,especiallyurban,muchconstructioniscarriedoutinessentiallysimilargroundconditions.Sincegeotechnicalsiteinvestigationisconsideredexpensive,data-basesofexistinggroundinformation,publiclyaccessible,aredesirable.Generalacceptanceandtheinvolvementofpolicymakersareneeded,andtheprocessofdevelopingcompre-hensiveandreliabledatabaseswillprobablytakemanyyears.Furthermore,itwillneverend,becausecontinuousupdatingwillbeneededasnew,andhopefullybetter,databecomeavailable.
Thedataofbasiclaboratoryteststhatarehighlyrepeata-bleandreproducibleamongdifferentlaboratoriescouldreadilybeincludedinadatabase.Ontheotherhand,constructionofadatabaseofadvancedlaboratorytestswouldneedcarefulqualitycontrol,orverydiscerninguse.Theinformationcouldbestoredingeographicinformationsystems,whichcouldalsobeusedasastoreforreal-timemonitoringdata,probablywithrestrictedaccessinitially.Throughtheinternet,databasescouldeffectivelybelinked,makingverylargequantitiesofinformationavailabletoeveryengineer.Highlydevelopedcomputationalprocesseswillthenbeneededtofindrelevantdataforaparticularsituation,tocategorisetheirquality,andtointerpretthem.Fieldreconnaissance
Inadditiontotheiruseinderivinginsituparameters,geophysicalmethodssuchas3Dtomographyarealsorele-vant,andlikelytobeincreasinglyused,forsitereconnais-
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sancetoidentifystratification,bouldersandvoids.Theenormousvalueoffieldinspectionsiswellknowntogeolo-gistsandgeotechnicalengineers,butitisexpensive,espe-ciallyinglobalactivitieswheresitesmaybeveryremotefromtheexpert’sbase;atthelimit,thesitecouldevenbeonanotherplanet.Developmentsinelectronicsandcommu-nicationsarelikelytobeveryrapid,andfutureapplicationsofthesecouldbeimagined.Forexample,ageologicalrobotmightbedeveloped,deliveredtositeonalorry,submarineorspaceship.Itwouldbeabletoassembleandpropelitself,takesamplesandcarryoutfieldtestssuchasgeophysicalandpenetrationtests,providedetailedphotographsandmicrographs,analyserockjointinginexposures(perhapsbysendingaflyingprobeuptherockface),andsoon.Allthismightbecontrolledinteractivelyfromanofficeatgreatdistance,makingtop-qualityhumanexpertisereadilyavail-ableanywhereintheworldatacceptablecost.
DESIGNANDANALYSIS
Thegeotechnicaldesignprocessusuallyinvolvesassimila-tionofdata,areviewofcasehistoryexperience,codesofpracticeandempiricaldata,andsomecalculations,leadingincombinationtodesigndecisions.Thisbasicprocessisnotexpectedtochange,butfeaturesinwhichdevelopmentsmightbeexpectedarenotedbelow.
Numericalmodelling
Itislikelythatfiniteelementanalysiswillcontinuetobeused,bothforserviceabilitycomputationsandforstudiesoffailuremechanisms.Thismightlargelyreplacetheuseoflimitequilibriummethods,withadvantagesthatfeaturessuchasthreedimensions,timedependence,anisotropy,pro-gressiveandpost-peakbehaviourcouldbeincluded(e.g.Kovacevicetal.,2007).
Fordesignpurposes,numericalmodellingrequiresreliablesoilconstitutivemodels,reliabledataonstrataandsoilproperties,andadequatecomputationalpower.Atpresent,computationalpowerisoutstrippingsoilmodelling,withtheprospectofrelativelyeasyaccesstoverylarge3Danalyses.However,asdiscussedabove,thedevelopmentofsoilmod-elsismuchmoredifficult,andcontinuedresearchwillbevitaltopracticaluse.Intelligentapplicationofthelimitedcapabilitiesofavailablemodelswillbecriticallyimportant,andpossibilitiesofmisusemaybeanincreasingdangerassoftwarebecomesmoreaccessible.
ItisunlikelythatDEMwillbecomeapracticaltoolfortheanalysisofgeotechnicalconstruction,butitispossiblethatitcouldbeusedtoinvestigatesomesoilproblemsinvolvingsmalldetailsofbehaviour.Examplesmightincludetheper-formanceofaugersandotherformsofblade,orproblemsofsandinginoilwells,whereacombinationofreductioninporepressureandhighhydraulicgradientleadstocrushingofsandstoneandparticledisplacement(Lietal.,2006).Neuralnetworks
Greatercomputingpowerenablesengineerstocarryoutexistingmethodsofanalysismorequickly,andtoextendthem.Thepossibilityofcompletelynewmodesofanalysisandthought,whichcomputersmightmakeavailable,havebeenlittleexploredtodate,butcouldhaveabigimpactincomingdecades.Amongthesearetheuseofneuralnet-works,whichhavebeeninvestigatedasanewmeansofcapturingessentialfeaturesofsoilbehaviourtobeusedinanalysis.Toll(2001)reviewedtheuseofneuralnetworksingeotechnicalengineering,andreportedthatthemainusewasinclassificationandparameterassessmentandinfoundation
design.Recently,furtheruseofneuralnetworkshasbeenreportedinestimatingthedeflectionofdiaphragmwalls(Kungaetal.,2007)andtunnellingperformance(YooandKim,2007).Itisconceivablethattheseorsomesimilarcomputer-basedsystemsmightprovidesuperiorbrains,whichcanassimilatetheverycomplexdatacurrentlyavail-ableaboutsoilbehaviour,andusethemtoprovideusefulpredictions.Adisadvantagemightbethatthedegreeofunderstandingtransmittedtohumanengineersmightbereduced,which,regrettably,mightbeacommonfeatureoffuturepractice.
Statisticalmethodsandriskanalysis
Inrecentyears,thespecificidentificationofrisks,forexampleinformingriskregisters,hasbecomeaprominentpartofthedesignprocess.Havingacommonlanguageforrisk,withclearunderstandingbetweenclients,designersandconstructors,isvaluableanddeservesmoredevelopment.Itisalsodesirable,whererealisticallypossible,toquantifyrisk,inrelationbothtoeconomicissues,suchasdelaysincontracts,andtosafety,whichcouldrelatetothederivationoffactorsofsafetyincodesofpractice.Thenecessarybalanceingeotechnicsbetweentransparencyofprocess,clarityofdata,andthebestuseofexperienceandtraininghasbeendiscussedintextssuchasDegreesofBelief(Vick,2002)andinconferencessuchastheFirstInternationalSymposiumonGeotechnicalSafetyandRiskatTongjiUniversityin2007(e.g.Faber,2007).
Inthegeoenvironmentalfield,statisticalanalysisiscom-monpractice.However,forthedesignofconventionalgeotechnicalstructures,althoughstatisticalanalysescanprovidesomeusefulindications,mostresearchershavefoundthatthecomplexityofthegeotechnicaldesignprocessissuchthatitcannotbereducedtoacomputationalprocess,sohumanjudgementandexperience,thoughoftenlackingcompletetransparency,arevitalelements.Itisexpectedthatresearchinthisareawillcontinue,andwillinfluenceprac-tice.Withever-morepowerfulcomputers,databasesandlogicalalgorithms,itmaybethatriskswillbeanalysedwithgreaterrationalityandconfidencethanispossibleatpresent.Relatedtothis,andwithmajoradvancesinmonitoringsystems,moreuseoftheobservationalmethodcanbeexpected,usingreliabilityanalysistoensurethatsafetylevelsarenotdiminished.
Codesofpractice
Assessmentofgroundproperties,arguablythemostim-portantaspectofgeotechnicaldesign,isnoteasilyreducedtoacodeofpractice,sogeotechnicalcodestendtoactaschecklists,givingoverallguidanceaboutprocedurestogetherwithsomefactorsofsafety.Recentlysomeinternationalcodes,suchasEurocodes,haveattemptedtodefinetheprocessofderivingdesignvaluesofparametersinordertoprovideacceptablemarginsofsafetyandperformance.Atpresenttheproceduresrelyheavilyonhumanknowledgeandexpertise,butitcouldbethatthedevelopmentofinformationdatabases,togetherwithmajordevelopmentsinartificialintelligence,willallowmuchofthisprocesstobecarriedoutbycomputer.Whetherusedbyhumansor
computers,thepast60yearsofGe
´otechniqueandotherjournalsisavitalpartofthedatabase.
Thereremainsmuchtobedebatedabouttherelativeimportanceofserviceabilityandultimatelimitstatesingeotechnicaldesign,aboutwherepartialfactorsofsafetyshouldmostlogicallybeapplied(Paikowsky,2004;Schuppener,2007;Simpson,2007b),aboutthepartthatcanbeplayedbyprobabilityanalysis,andabouttheroleof
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performance-baseddesign(Honjo&Nagao,2007).Intheshorttermthereisadangerthat,amidstthisdebate,muchofthepracticalgoodsenseofexistingcodescouldbelost.Muchworkremainstobedonetoensurethataccumulatedknowledgeisusedsuccessfullywiththerelativelynewsafetyconceptsincurrentcodes.Inthelongerterm,itisreason-abletohopethatideasabouttheapplicationofsafetyfactorsandmarginswillcontinuetoconverge.Thiswillrequireasignificantcollaborationoftheresearchcommunityandpractice,andundergraduateteachingaboutthepurposesandmagnitudesofsafetymarginsindesignwillbeneededtoinformbothusersandfuturedevelopersofthecodes.
Asnotedearlier,civilengineeringuseslargeamountsofenergy,muchofitembodiedinthematerialsused.Economyindesignwillbeessential,affectedbythemagnitudesoffactorsofsafety,amongotherfactors.Societywillthereforeneedcodesofpracticetoadopttheminimumacceptablefactorsofsafety,whichcouldleadtoprogressiverefinementofthecodes.DISSEMINATION
Untilrecentyears,technologicalunderstandinghasbeentransmittedmainlyinthreeways:throughthewrittenwordonpaper,vialecturesinteachingandconferences,and‘on
thejob’asknowledgeispassedbetweencolleagues.Ge´o-techniquehasbeenaleadingorganofthefirstofthesemethods,andengineershavereliedheavilyonjournalsandtextbooks.Morerecently,computer-basedknowledgehasbecomeprominent,especiallyfromtheinternet.Papersfromjournalscanoftenbeobtainedfromtheinternet,althoughthisisnotyetgenerallytrueofconferenceproceedingsandtextbooks.YoungengineerssearchingforinformationarelikelytoappealfirsttoGoogleorWikipedia,andthentopapersonline,beforefinallyresortingtopaperpublicationsifnecessary.Commercialcompaniesseeasavinginthis,becausestoragespacefordocumentscanbereduced.Issuesofcopyrightondownloadeddocumentsaddanunfortunatecomplicationforbothpublishersandusers.On-lineforumsareactive,andmaybecomeincreasinglyinfluential;geotech-nicalengineershavetraditionallybeengenerousinsharingtheirknowledgeandinformation.
Peer-reviewedjournalssuchasGe
´otechniqueplayanimportantroleinprovidingreaderswithinformationthathasbeenthoroughlyvettedandsoislikelytobereliable.Thejournalsarealsoimportantinprovidingacontrolledoutletforacademicpublications,whichmeasuretheachievementsofresearchersandsoenablethemtoobtainfundingforfurtherwork.Itisimportantthatthesetworolescontinueinthefuture,althoughthisdoesnotnecessarilyrequirepublica-tiononpaper;similarpeerreviewcouldbeappliedtopaperspublishedmainly,oronly,ontheinternet,anditislikelythatdevelopmentwillproceedinthisdirection.Somemeansofguaranteeingthelongevityofthepublicationswillbeneeded.Internetjournalswillbesomewhatdifferent,con-tainingdirectlinkstootherdocumentsanddata,andperhapsinvitingdirectcommunicationwiththeauthors.
JournalswithaninternationalreadershiparepublishedmainlyinEnglish,butdifferencesoflanguageprobablysupportthesuccessofarangeofjournalsinvariouslanguagesdevotedtothesamesubject.Thiscanbefrustrat-ingforbothauthorsandreaders,impedingthespreadofideas.Itislikelythatonelanguagewillbecomeevenmoreubiquitousinthecomingdecades,anditisalsopossiblethatcomputerisedtranslationwillbecomesopowerfulthatread-erscanobtainajournalinanylanguagetheychoose.Thismightleadtoareductioninthenumberofjournals,butwouldenhancethetransferoftechnology.
Apartfrompublication,humaninteractionisimportanttodissemination.Inordertoidentifyreliablementors,students
andusersofinformationneedsomepersonalconnectiontothem,solecturesandconferencesarelikelytoremainimportant.However,itcouldbethattravel,especiallyinter-nationally,willbecomemoreexpensive,andvariousformsofvideoconferencingmaytakeprecedence.Atpresentthisisoftenunreliableandimpersonal,butitcanbeexpectedthatveryrapidinteraction,stimulatingpersonalinterchange,willbeavailableinthenearfuture,greatlyreducingtheneedfortravel.Nodoubtsuchadevelopmentwillbeconsideredbothconvenientanddisappointing.
CONCLUDINGREMARKS
Thefutureofgeotechnicalconstructionislikelytobeveryactive,involvingtheapplicationofcurrentlyacceptedprocessesandmanydevelopmentsaimedatreducingenergyconsumptionandcarbondioxideemissions.Thesecon-straintsapplybothtoconstructionprocesses,requiringtheminimisationofembodiedenergy,andtotheprovisionofconstructionsthatwillhelpsocietyuselessenergy,orgener-atemoreenergyfromnon-carbonsources.Geotechnicalengineerswillembraceexpertiserelatedtoheattransferintheground,withimportanthydrogeologicalconnections.Engineeringofdeeprepositoriesfornuclearwastewillinvolvegroundmaterialsathighstresseswithchangingtemperaturesanddegreesofsaturation,andconsiderationofthemovementofradionuclidesintheground.
Moreresourcefuluseoffillmaterialsisenvisaged,withgroundimprovementandgeosyntheticsplayingimportantroles.Thebehaviourofsoilisincreasinglyunderstoodtobeverycomplex,andcontinuedresearchintothiswillbenecessary.However,bringingtheresearchintopracticalapplicationremainsverychallenging,andislikelytobesoformanyyearshence.Experienceandempiricismwillcontinuetobeessentialtogeotechnicaldesign.
Furtherrapiddevelopmentofelectronicsandcommunica-tionsisexpectedtofacilitatemajoradvancesinlaboratoryandfieldequipment,monitoringandobservationalap-proaches,andthepossibilityofremotesitereconnaissancehasbeensuggested.
Designprocesseswillbecomemoreheavilyreliantoncomputersasdatasourcesandcalculators.Itisnotcleartowhatextentartificialintelligenceandcomputerisedprocessesofriskanalysismightreplacetheexpertiseofthehumanengineer.Thereisadangerthatengineerswillbecomedeskilled,withnoadequatereplacement.
ThefutureofjournalssuchasGe
´otechniqueisconsideredtobeveryimportantasacontrolonthequalityofpublishedinformation,whichalsohelpstoregulatethefundingofresearchandthecareersofresearchers.However,thenatureofjournalscouldchangeconsiderablyastheybecomemainly,ifnotentirely,electronicinnature.
TheauthorswouldliketowishGe
´otechnique,andthewholegeotechnicalcommunity,averysuccessfulnext60years.ACKNOWLEDGEMENTS
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