TELSTRAPERTHOCEANOUTFALLOIL/GAS|SEWER|STORMWATER|POWER|WATER|TELCO

LOCATION FloreatBeach,Perth

CLIENT Telstra

PIPE 149mmsteelconduit

GEOLOGY Sandandlimestone

LENGTH 800metres

TECHNIQUE HDD

PROJECTOVERVIEWTelstra,alongwithanumberofpartners,hascompletedaprojecttoinstallanewunderseatelecommunicationscablebetween Singapore and Perth named the Indigo West Cable. The cable system will provide a new route forcommunicationstrafficbetweenAustraliaandSoutheastAsia,significantlyimprovingconnectivityandstrengtheninglinksintofast-growingAsianmarkets.SCOPEOFWORKSTelstra engaged UEA to construct a new underground access chamber/manhole, and to bore a newtelecommunications conduit from Floreat Beach, 800metreswest/northwest to the seabed. The new conduit hasbeen used to connect to the underwater cable. Telstra obtained approval from the Western Australian PlanningCommission for this cable landing infrastructure development, with the work carried out in accordance with theapprovedEnvironmentalManagementPlandevelopedbyUEA.Inordertoundertakethiswork,UEAcompletedthefollowingactivities:

• Establishedasitecompoundanddrillsite• Installedsecurityfencingaroundthesitecompound• Horizontaldirectionallydrilled800metresofseawalltopredeterminedcoordinate• Installedcompletionpieceandbuoyontheseafloorusingadiveteam• Constructedanundergroundsteelreinforcedconcreteaccesschamber/manhole• RestoredthesiteinaccordancewithTownofCambridgestandards

DESIGNUsinganin-housedesignteam,UEAundertooktheinitialsurveyingfortheHDDdesignandbeachmanholedesign.Byusing a TrimbleGPS system,UEAwas able to accurately design the new submarine cable conduit in linewith thecapabilitiesoftheHDDrig.Usingthisdata,awirelinesystemwasemployedtotrackthedrillheadfromthebeachoutto the predetermined coordinates on the seafloor. Upon completion, additional data (coordinates and levels) wascollectedalongtheinstalledconduitforthefinalisationoftheworkasexecuteddrawingstobeprovidedaspartofthefinalqualityassurancereport.CONSTRUCTIONDuringtheoperation,thedrillingfluidwasconstantlymonitoredtoensurethatnolossoccurred,withbothxanthangumandfreshwaterusednearthedrillexitpointtoprotectmarinelife.Oncethedrillingwascomplete,UEAengageddivers to recover the drill head from the seabed. The divers pulled a rope through the drill rods and installed asubsurfacebuoy,andthedrillrodswereleftin-situtoactastheconduitfortheopticfibrecable.UEAconstructedaconcreteaccesschamberaroundthenewconduit,andwiththefinalrestorationofthesitetocompletetheproject.CHALLENGESANDCOMPLETIONThe sandy ground conditionsmade it difficult tomobilise and setup the equipment. In order tomanage the softground, a 100 tonne cranewasutilisedduringbothmobilisation anddemobilisation to assistwith the loading andunloadingoftheHDDequipment.Heavydutytrackmatswereutilisedtoprovideaccesstositeforvehicles,andsteelcasingwas installed from theentrypoint to the limestoneaspartof theHDD.Thiswasa totalof thirtymetresofcasingthroughthesandygroundtolimestoneinordertoeliminatetheriskofboreholesubsidence.Roughseasduringtheprojectmadeitdifficultforthediverstoworkontheseafloor.Theswellwashigh,andcoupledwithrelativelyshallowwaterdepth,makingitdifficultforthediverstoremainsteadywithvisibilitypoorattheHDDexitlocation.Evengiventhesechallenges,theprojectwascompletedsuccessfullywithanoveralldurationoffourweeks.