NORTHLISMOREPLATEAUSTAGE1WATERMAINHDDOIL/GAS|SEWER|STORMWATER|POWER|WATER|TELCO

LOCATION TulleraReservoirNSW

CLIENT LismoreCityCouncil

PIPE 355mmand280mmPN16polyethylene

GEOLOGY Claywithboulders

LENGTH 1,589mof280mm&1,423mof355mm

TECHNIQUE HDD,pilotboring

PROJECTOVERVIEWNorth Lismore Plateau (NLP) is approximately three kilometres northwest of Lismore’s CBD, an areaidentified for futuregrowth.Thedevelopment is expected to yield2,079dwellings including commercialand retail properties.UEA’s consolidated thewatermain requirements for the newdevelopment of theNLP,inordertoutilisetheexistingsparecapacitywithintheTulleraWaterReservoirtoserviceupto300newresidentialdwellingswithinthedistrict.SCOPEOFWORKSThe project included the installation of 1,589metres of 225mmand 1,423metres of 300mmPN16 PVCwater main by open trench. UEA proposed an alternate method of installation by utilising horizontaldirectional drilling (HDD),which council approved.Due to the installationmethod changing, theproductpipe also had to be converted to 280mm (225mm Internal) and 355mm (300mm Internal) PN16Polyethylene(PE)pipe. Inaddition,430metresof125mmsleevewith40mmproductpiperoadcrossingswereinstalledusingHDDtoreplacetheexistingserviceconnections.UEA utilised a DitchWitch AT3020 to perform the works. The benefits of using this drill were its smallfootprint,aswellasitsabilitytodealwiththeexpectedchanginggroundconditionsatthislocation-softclaysandrock.Thegroundconditionsproveddifficultbutacombinationofgooddrillingpractise,gooddrillfluidmanagementandexcellentreamerchoiceensuredthenewpipewasinstalledinlinewiththeclient’sprogramme.UEA’scivilcrewthenlinkedupallthenewpipe,installedhydrants,airvalvesandscourpits.Each house was then connected to the existing system with all testing, flushing and commissioningcompletedsatisfactorily.

COMPLETIONManydifficultieswereencounteredduringthedrillingprocess,someofwhichincluded:

• Large extremely hard floating boulders. These boulderswere difficult to drill through, especiallywhenthesurroundinggroundconditionsweresoft.Ratherthanchangingdrillheadsandpossiblydamagingcuttingteeth,UEAdugupandremovedeachrockbeforecontinuingtodrill.Duetotheshallowdepthofthemain,digupswerenotanissue.

• Reactive and soft ground conditions. At the start of the project, this combination of groundconditionsandtravellingatshallowdepthsmeantthatthesurfacelevelhumpingbecameanissuethatcouldcausemajordamage.Utilisingknowledgewithinthecompany,themethodsandtoolingwere altered and boring longer shots of large diameter was possible without any damage toexistingsurfacelevels.

• Temporary traffic lights toshutdownone lane.Traffic lightswerenotable tobe turnedonuntil9:00eachmorningduetolocaltrafficrestrictions,soadditionalstaffwererequiredeachmorningtooperateStop/Gountilthelightswereabletobeturnedon.

Between the extensive knowledge of UEA’s team, and a close working relationship with council, theseissueswereovercomewithnoeffecttotheprojectfortheclient.