8
back SYSTEMS OF TRENCHLESS TECHNOLOGY Trenchless Technology Systems for underground utility services fall into three broad categories: 1. Installation of a new pipeline or duct, including dealing with service connections; 2. On line replacement of an existing pipeline or duct; 3. Renovation of an existing pipeline or duct. A number of essential services required prior to the selection of the trenchless system, are associated with these systems like: Site investigation to determine soil and groundwater conditions; Inspection to determine the condition of the pipeline; Location survey to determine the position of existing pipelines, other services and potential obstacles. Trenchless Technology is concerned largely with services too small to permit man entry, generally up to about 900mm diameter. These constitute 99% of all underground pipes and ducts. This introduction does not deal with large tunnels and processes such as segmental lining or timber headings where men are required to work at the tunnel face. In most trenchless systems the skill and experience of the operator is important. Specialist manufacturers and contractors recognise the need for full operator training and a certification scheme is desirable. NEW INSTALLATIONS Methods for the installation of a new pipeline or duct, including dealing with service connections, are: Microtunnelling Short Drive Systems Horizontal Directional Drilling Guided Drilling Microtunnelling Controlled Excavation Steerable less than 1000mm diameter Medium LengthMicrotunnelling is used here as a general term to describe remotely controlled mechanical tunnelling systems where the spoil is removed from the cutting head within the new pipeline which is advanced by pipe jacking. Microtunnelling machines have now been developed to work from drive shafts in almost all types of ground conditions. However, it is essential to know what these conditions are likely to be as

System of Trenchless Technology

Embed Size (px)

DESCRIPTION

System of Trenchless Technology

Citation preview

  • 3/29/2015 Thecountryandthepeople

    http://awas.up.nic.in/WEBSite%20%20New%20technologies/trench%20less%20technology.htm 1/8

    back

    SYSTEMSOFTRENCHLESSTECHNOLOGY

    TrenchlessTechnologySystemsforundergroundutilityservicesfallintothreebroadcategories:

    1. Installationofanewpipelineorduct,includingdealingwithserviceconnections

    2. Onlinereplacementofanexistingpipelineorduct

    3. Renovationofanexistingpipelineorduct.

    A number of essential services required prior to the selection of the trenchless system, areassociatedwiththesesystemslike:

    Siteinvestigationtodeterminesoilandgroundwaterconditions

    Inspectiontodeterminetheconditionofthepipeline

    Location survey to determine the position of existing pipelines, other services andpotentialobstacles.

    TrenchlessTechnologyisconcernedlargelywithservicestoosmalltopermitmanentry,generallyup to about 900mm diameter. These constitute 99% of all underground pipes and ducts. Thisintroduction does not deal with large tunnels and processes such as segmental lining or timberheadingswheremenarerequiredtoworkatthetunnelface.

    In most trenchless systems the skill and experience of the operator is important. Specialistmanufacturers and contractors recognise the need for full operator training and a certificationschemeisdesirable.

    NEWINSTALLATIONS

    Methods for the installationofanewpipelineorduct, includingdealingwithserviceconnections,are:

    Microtunnelling

    ShortDriveSystems

    HorizontalDirectionalDrilling

    GuidedDrilling

    Microtunnelling

    ControlledExcavationSteerablelessthan1000mmdiameterMediumLengthMicrotunnellingisusedhereasageneraltermtodescriberemotelycontrolledmechanicaltunnellingsystemswherethe spoil is removed from the cutting head within the new pipeline which is advanced by pipejacking.

    Microtunnellingmachineshavenowbeendevelopedtowork fromdriveshafts inalmostall typesof ground conditions. However, it is essential to knowwhat these conditions are likely to be as

  • 3/29/2015 Thecountryandthepeople

    http://awas.up.nic.in/WEBSite%20%20New%20technologies/trench%20less%20technology.htm 2/8

    theywill determine the typeofmachine tobeused, the cuttinghead, the spoil removal system,andthejackingforceslikelytoberequired.

    Thecuttingheadhastobecarefullyselectedtodealwiththeexpectedgroundconditions,withtheappropriatecuttingtoolsandcrushingdevicesfortherangeofgravels,sands,silts,andclays.

    The only excavating required from the service is for drive and reception shafts. Spoil may beremoved from the facebyanauger running through thenewly installedpipeline toa skip in thebaseofthedriveshaft.

    Alternatively,water or bentonitemay be used to convert the soil into slurry at the cutting face.The slurry is then pumped to the surface where the solids are separated before disposal. Bothsystemsprovide face support bymechanical earth pressure balance.Slurry pressure at the facecanalsobeusedtocombatexternalgroundwater.

    Withsomesystems,controlisexercisedautomaticallybutmicrotunnellingmachinesaregenerallyoperated from a control console in the cabin at the surface. The location and orientation of themachine is continually monitored, usually by means of a laser guidance system. Accuracy indrivingusuallydependson the skill andexperienceof theoperator, especially in varyinggroundconditions.

    Microtunnelling is used extensively for sewerage work where surface disruption has to beminimised.Itprovidesthenecessarydegreeofaccuracy ingravity lines.Ifaschemeisdesignedwith a trenchless solution inmind the drive and reception shafts can be locatedwhere they canbecomemanholes in the finishedscheme.Theymayalsobesitedtominimisedisturbanceof thehighwayandtrafficdisruptionduringconstruction.

    Considerableadvanceshavebeenmadeinrecentyears.Machinesarenowavailabletodrive100mormore insoftground forsizesof100mmdiameterupwards, fromdriveshaftsof less than3mdiameter. Theuseof laser guidance control systemsand computermonitoring, allied to steeringcapability,hasenabledahighdegreeofaccuracytobeachieved, typicallywithin+/25mm.It isoftenthecasethatmicrotunnelledsewersare installedtoahigherdegreeofaccuracythanthoselaidinconventionaltrenchesandthepipesaremoreevenlystressed.

    With the development ofmicrotunnelling, both concrete and clay pipes have been designedwithjackinginmind.Pipesinallconventionalmaterialsareproducedwithinwalljointsandinshorterlengths to enable smaller drive shafts to be used, thus reducing excavation volumes and roadoccupancy.

    Microtunnelling systems have been developed in which temporary steel tubes are jacked in andremovedatthenextmanholeposition,thenewpipelinefollowingintheestablishedbore.

    Muchattentionhasbeengiventoreducingtheimpactofpipelineconstructionontheenvironment.Often, the only indication on the surface is the presence of a control container with a hoist forlowering pipes into the drive shaft. Noise levels and traffic disruption are minimised. Both theextentanddurationofanyroadoccupancy isoftenasmall fractionof thatrequired ifatrenchedmethodofconstructionhadbeenadopted.

    ShortDriveSystems

    EssentiallyUnsteeredSoilDisplacement

    In urban areas numerous house connections and other short drives are carried out bymeans ofrelativelyinexpensiveunguidedsystemswithlowmobilisationcosts.Eveninopencountrywhereatrenched pipelinemay provide a least cost solution, there is often a need for short crossings ofobstacles.

  • 3/29/2015 Thecountryandthepeople

    http://awas.up.nic.in/WEBSite%20%20New%20technologies/trench%20less%20technology.htm 3/8

    Auger Boring utilises a rotating head to excavate the soilwhich is transportedbyauger flightsoperating inacasing tothe drive pit. The head is recovered at an exit pit or in thetrenchcut for theadjacent lengthofpipeline.Augerboring isusedintherangeof1001000mmdiameter.

    Impactmoling,inwhichapercussivemoleislaunchedfromadrivepittodisplacethesoilandformabore, iswidelyused.The new conduit is normally drawn in behind the mole.Pneumatically drivenmoles, inwhich the soil is displacedby

    the action of a percussive piston, have been developed in the range 30 80mm diameter for asingleoperation,withrepetitivemultiplepassestoachieve200250mmdiameter.Theyareusedto install services for all utilities. Moles are commonly used by gas and water undertakings forinstallations of up to 40m under roads, drives and gardens inmaking 4565mm diameter houseconnections.

    RodPushingisatechniqueinwhichaboreofabout50mmdiameterisformedbydisplacement.Arod is advanced by a straight hydraulic push and the pilot hole may be backreamed to therequired size. The technique is used for the installation of pipes and conduits up to 150mmdiameteroverlengthsof3040m.

    Pipe Ramming and Thrust Boring are similar processes where a casing, usually steel, is driventhroughtheground fromthedrivepit to theexitpit. InPipeRamming, thecasing isdrivenbyapneumatichammerwhilstinThrustBoringitisadvancedbyastraighthydraulicpush.Forsmallerdiametersthecasingmaybeclosed,butinthelargersizesspoilisremovedfromtheopenendedcasingbycompressedairandwater.

    HorizontalDirectionalDrilling

    SteerableHeavy,powerfulriglargesizerangeLongdistances

    Horizontal Directional drilling systems were originallydeveloped by the oil industry for river crossings of smalldiameter where no high degree of accuracywas required.They are now widely used for installing pressure pipesunder major obstacles such as motorway intersections,largeriversandairportrunways.

    Asmallrotatingandsteerabledrillbitislaunchedfromthesurfaceatanangleof1015(andisusedtodrilla90mmdiametermudfilledpilothole.Duringthedrillingoperation

    a125mmdiameterwashoverpipeisdrilledoverthepilotstringandfollowingsome100mbehindthehead.Alternatedrillingthencontinuesonthepilotstringandthewashoverpipeuntil theexitpointonthefarsideoftheobstacle.

    Thepilotstring is removedand thebore isenlargedbya rotatingbarrel reamerattached toandpulled back by the washover pipe, drilling mud being used to flush away the cuttings and tosupport the reamedhole.Subsequent reaming continuesuntil the requireddiameter is achieved.Theproductpipeisthenattachedtothereamingheadandpulledthroughthebore.Drivesofmorethan1.5kmandofupto1200mmdiameterhavebeencarriedout.

    GuidedDrilling

    SteerableSmallRigShallowDrillingMediumLength

    Guideddrillingemploysanexcavationorsoildisplacementheadwithcompact lightweightrigforrapidmobilisation.Smalldiameter jets,mechanisedcutting toolsordisplacementheadsattached

  • 3/29/2015 Thecountryandthepeople

    http://awas.up.nic.in/WEBSite%20%20New%20technologies/trench%20less%20technology.htm 4/8

    toaflexibledrillstringarepositionedtoformaboreasthehead is thrust forward. The drilling head is launched fromthe surface at an inclined angle. Steering, in both verticaland horizontal planes, is effected by controlling theorientationofaslantfaceatthehead.

    For a straight bore the drill string is continually rotated.Whenadeviationisrequiredtherotationisstoppedandtheslant faceorientated toproduce the requireddeviation.Thedrill string is then pushed forward. With the drill string

    rotating oncemore, excavation or displacement is continued. Monitoring of the alignment takesplaceusingatransmitterintheheadandalocatingdeviceatgroundlevel.

    Havingestablishedthepilotbore,backreamingequipmentisdrawnthroughtheholetoenableittoaccepttheproductpipe,ductorcable,usinganimpactmoleorwinchwire.

    ONLINEREPLACEMENT

    Methodsofonlinereplacementare:

    Pipebursting

    PipeEating

    PipeBursting

    NewforOldwithoutTrenchingSizeforSizeandUpsizeCapability

    Inurbanareasthetop1mbelowthesurfaceisoftencongestedwithexisting services and chambers. This allows little scope forreplacementofadefectiveserviceonanewline.Theexistingholeinthegroundthusbecomesvaluableasaroute.

    PipeBursting,sometimescalledPipeSplitting,hasbeendevelopedto exploit this resource. Initially the aim was for sizeforsize

    replacementbysplittingthedefectivepipeanddisplacingthefragmentstoenableanewpipelineof the same diameter, usually of polyethylene (PE), to be drawn in. However, many defectivesewers were found also to be overloaded and replacement sewers of increased capacity wererequired.

    In thegas industry increasedcapacitywas tosomeextentprovidedbyconversion tonaturalgaswith its higher calorific value. However, in many places there was an urgent need to replaceageingcast iron(Cl)mainswithpoor jointsby lowandmediumpressuremainswithaminimumnumberofjoints.

    Extensive proving work by the gas and water industries has demonstrated the feasibility ofupsizinggasmains,watermainsandsewers.Anexpandingdevicewhichmaybeeitherpneumaticorhydraulic, is introduced into thedefectivepipeline,shatteringthepipeanddrawing in thenewline. Insertion of short lengthsmay bemade from pits but this involves jointing of the pipeline.This can be avoided by the use of silt trenches to insert pipe strings. Upsizing from 100mm to225mmdiameterisnowwellestablished,andpipesofupto600mmdiameterhavebeenreplaced.

    Any side connections must be disconnected in advance. In the case of sewers they are oftenreplacedbyshortridersewersconnectingtomanholes.

    PipeEating

  • 3/29/2015 Thecountryandthepeople

    http://awas.up.nic.in/WEBSite%20%20New%20technologies/trench%20less%20technology.htm 5/8

    NewforOldwithoutTrenchingEnlargementSteerable

    PipeEating isanonlinemicrotunnelled replacement technique.Theexistingdefectivepipeline iscrushed and removed through the new pipeline. Lateral connections must be disconnected inadvanceandmaybereplacedbyridersewersorreconnectedbyangleddrilling.

    RENOVATION

    Wheretheperformanceofthepipelineisunsatisfactory,butthefabrichasaresidualvalue,eitherstructurally in its own right or as a lining support, renovationmay be appropriate. An essentialpreliminary is to determine the condition of the existing pipeline. From hydraulic analysis andstructuralinspectionitmaybeconcludedthatapipelineis:

    Structurallyweakor

    Structurallysound,buthydraulicallydefective.

    Ineithercaseitisoftenmoreeconomictorenovatethedefectivepipethantoprovideanentirelynewone.

    Renovationmethodsare:

    Sliplining

    LiningFormedinPlace

    SprayOnLining

    LocalisedRepair

    ChemicalStabilisation

    Sliplining

    NewforOldwithoutTrenchingLongLengths

    Sliplining was one of the earliest forms of continuousstructural lining. A new pipeline of smaller diameter isinserted into thedefectivepipeandtheannulusgrouted.It has the merit of simplicity and is relativelyinexpensive. However, there can be significant loss ofhydrauliccapacity.

    Modified Sliplining, often called close fit lining, includingRolldown, Swagelining and Deformed Lining, utilise theproperties of PE or PVC to allow temporary reduction indiameter or change in shape prior to insertion in thedefectivepipe.The insertedpipe is subsequentlyexpanded to forma tight fit against thewallofthe original pipe, thus avoiding the need for annulus grouting as in conventional sliplining. ForRolldownandSwageliningtemporaryreductionindiameterisachievedeitherbymechanicalrolling(Rolldown) or drawing through a reduction die (Swagelining). For Deformed Linings the pipe isdeformed and folded immediately after extrusion and is coiled on a drum. After insertion in thedefectivepipetheliningisexpandedusingsteamandareroundingdevicetoformaclosefit.

    These systems are suitable where the existing line is of good shape. When improved hydraulicperformanceistakenintoaccount,itissometimesfoundthatthereislittleornolossofcapacity.

  • 3/29/2015 Thecountryandthepeople

    http://awas.up.nic.in/WEBSite%20%20New%20technologies/trench%20less%20technology.htm 6/8

    LiningFormedInPlace

    StructuralRenovation

    Awidelyusedstructural renovationsysteminvolvesaresin impregnatedsockbeing inserted intothepipeorconduit(notnecessarilycircular)andsubsequentlyforcedagainstthewallusingwaterorairpressuretoprovideacontinuousthinlining.

    Curingoftheresinmayoccurnaturallyormaybeacceleratedbyheatorultravioletlighttoformaresilienttightfittinglining.Anylateralconnectionsarereopenedoncompletionandthereislittleloss of capacity. The system can accommodate larger radius bends and is used from 80mmdiaupwards. Currently only some systems have approval for use in potable water mains in somecountries.

    Wheretheintegrityofanexistingpressurepipelinecanberelieduponanditisonlynecessarytopreventleakage,aloosefitreinforcedhosemaybeused.Thisispulledthroughtheexistinglineinacollapsedstateandpressurisedwheninposition.Thesystemhasapplicationforpipelinesintherangeof100mm355mmdiameter.

    Asystemusingspirallywoundplasticlininghasbeendevelopedfordefectivesewers.ThisusesacontinuousPVCprofilestripwhichmaybeintroducedbyahelicalwindingmachineatthebottomofamanholeintoagravitysewer.Ithastheadvantagesofnotrequiringspecialroadopeningsandofbeing able to accommodate variations in cross section and large radius bends. It is usuallynecessary to grout the annulus and there is often significant loss of capacity. A variation of thesystemallowsexpansion, by reversewindingof an insertedundersized lining to forma close fitwith the existing pipe, avoiding theneed for annulus grouting. The systemhas beenused in therangeof100m2500mmdiameter.

    SprayOnLining

    CorrosionProtection

    This is a well tried and tested technique for applying either ananticorrosionorstructural liningtopipes.Ahighspeedrotatingheadiswinchedthroughthepipeline,centrifugallydepositingtheliningmaterialover the full internalsurface.Formorethan fiftyyears,cementmortarhasbeenusedforliningwatermainsfrom75mm diameter upwards, to prevent encrustation, discolouredwaterandlossofcapacity.Morerecentlyanepoxyresinmaterialhas been approved for use in potablewatermains and is beingusedforsizesupto600mmdiameter.

    Structural sprayon lining is a new concept in sewer rehabilitation, stemming from advances inequipmentandpolymerformulation.Thedefectivesewerreceivesahighbuildsprayliningofquicksetting epoxy resin or polyurethanematerial. The operation is carried out from the surface andfromwithinexistingmanholes thusavoiding roadopenings. Ithasbeendeveloped foruse in therangeof150mm600mmdiameter.

    LocalisedRepair

    ResinInjectionandChemicalGroutingatTroubleSpots

    Local defects may be found in an otherwise sound pipeline, due to cracking or joint failure.Systems are available for remote control resin injection to seal localised defects in the range100mm600mmdiameter.

    Chemical Grouting with urethane and similar materials has been used for many years in sewer

  • 3/29/2015 Thecountryandthepeople

    http://awas.up.nic.in/WEBSite%20%20New%20technologies/trench%20less%20technology.htm 7/8

    rehabilitation, particularly in North America. Remote and manentry grouting of defective jointsand cracks may prevent infiltration and the formation of external voids in an otherwise soundpipeline.

    ChemicalStabilisation

    RestoringSupportforSewers

    Thestabilityofsewersindoubtfulgroundconditionsmayberestoredbytreatingmanholelengthswithatwopartchemicaldosing.ThesewerlengthissealedandfilledfirstwithsolutionAwhichisthenpumpedoutandrefilledwithsolutionBwhichisalsosubsequentlypumpedout.Thechemicalreactionbetweenthecomponentssealsjointsandcracksinthepipeandstabilisesthesurroundingsoil.

    SITEINVESTIGATION

    Inthepreparatoryworkforinstallinganewserviceitisimportantthatadequateanddetailedsiteinvestigation with relevant material testing be carried out and that the information and itsinterpretationbemadeavailabletothecontractor.Incomparisonwithtrenchingmethodsthedepthoftenhasmuch less influenceon costwhere trenchlessmethodsareadopted.Therefore there isfrequentlymore flexibility in the choice of depth of themain or service. Both the depth and theroutearebestnotdetermineduntiltheresultsofthesiteinvestigationareknown.

    Becauseoftheimportanceofhavingadequateknowledgeofthegroundandofthelocationofanyexisting services, there is often justification for the expenditure or more money on advancesurveysthanwouldbethecasewithopentrenchingmethods.

    CONDITIONSURVEY

    The structural condition and hydraulic capacity of an existing conduit determines the type ofrehabilitation required. Thus, when there is doubt concerning the condition of an undergroundnetwork,itisimportanttocarryoutaCCTVsurvey.Theinterpretationofthevisualrecordisalsoimportant.Trainingandexperiencearerequiredforcorrectinterpretation.

    UNDERGROUNDDETECTION

    In many trenchless methods the position of the driving tool is continuously monitored using atransmitter in the driving head and a locater on the surface. However, the location of otherservicesmaycallforothertechniques.

    Detection of ferrous metal services from the surface is possible using location devices readilyavailable.ForPRandothernonferrousservices,ifnotracerwirehasbeenprovided,atransmitterpulledthroughthepipelinemaybeasimplewaytolocatepositionanddepth.

    Thermography,orThermal Imagery,andGroundMappingRadarare techniqueswhichhavebeenusedtoalimitedextenteitherfromthesurfaceorfromwithinapipelinetolocateobstacles,voidsorotherservices.Interpretationofthevisualdataproducedrequiresskillandexperience.This isanareawherethereiscontinuingdevelopmentwithpromiseforthefuture.

    Moreinformationontrenchlesstechniquecanbeobtainedfromfollowingsociety:

    ISTT(Indiansocietyfortrenchlesstechnology)

    908,HemkuntChambers,89NehruPlace,NewDelhi110019

  • 3/29/2015 Thecountryandthepeople

    http://awas.up.nic.in/WEBSite%20%20New%20technologies/trench%20less%20technology.htm 8/8

    TelNo.91(11)51618094,Fax:91(11)51617863

    Email:[email protected]@indianodig.com

    back