THE RIGHT CHOICE FOR TRENCHLESS PROJECTS

uni-bell technical PUBLICATIONs u st a in a b le pipe infr a str u ct u re –it ‘ sourresponsi b ilit yPVCPIPETHE RIGHT CHOICEFOR TRENCHLESS PROJECTS

tingssignificantly increases real construction costs while greatlyThese “no-dig”impacting the indirect social costs that are associatedprocedures enable con-with interruptions to the flow of traffic and obstacles totractors to install pipe byboth businesses and the public. The construction of newtunneling or boring, thusunderground infrastructure, or the rehabilitation of oldgreatly minimizing thesocial costs associated withthe disruption to traffic,pedestrians, businessesand customers.infrastructure, presents the utility engineer and contractorwith the challenge of minimizing the impact of thesedisruptions on the surface, while making these neededimprovements underground.While open-cut installation proceduresconstruction typically involves smallcontinue to be the standard methodlocalized excavations from which theof construction for municipal pipinginstallation of pipe is completed byprojects, various trenchless technologyeither pulling or pushing of the pipelinedevelopments are making these optionsthrough pre-drilled bore holes or themore economically viable and appealing.existing pipe. Similarly, it is also possibleThese “no-dig” procedures enableto rehabilitate deteriorating municipalcontractors to install pipe by tunnelingpipelines without digging up the entireor boring, thus greatly minimizingline.the social costs associated with theprocesses can often restore bothdisruptionthe structural integrity and the flowtotraffic,pedestrians,businesses and customers. Trenchless Thetrenchlessrehabilitationcharacteristics of the pipe.

TRENCHLESS TECHNOLOGIESWELL SUITED FOR PVC PIPESSliplining, horizontal directional drilling (HDD), tight fit structural liner, andpipebursting are a few of the well-developed trenchless technology methodscurrently used for new construction and rehabilitation of pipelines.Theseconstruction techniques require piping products capable of withstanding largeaxial compressive and/or tensile forces. Through the development of severalinnovative joint designs, a number of PVC pipe producers offer pipe well suitedfor these trenchless pipe situations. The same properties that have made PVCthe market leader among pipe materials for water and sewer applications inNorth America make PVC a material of choice in the performance of trenchlessapplications. The wide acceptance of PVC pipe among municipalities for open-cutconstruction also makes PVC pipe a preferred and familiar choice for trenchlessinstallations in capital improvement projects as well as rehabilitation.TIGHT FITSTRUCTURAL LINERTight fit structural lining with PVC is accomplished by expanding a speciallyformulated C900/C905/ASTM D2241 PVC that has been butt fused together ina continuous length. It is inserted into the host pipe and then brought to tightfit dimensions through a combination of heat and pressure. The lining maintainsand/or increases flow capability by providing the C value of PVC that more thanoffsets the slight reduction in flow area.

PVC PIPE TRENCHLESSCONSTRUCTION OPTIONSThere are four trenchless technology methods for which PVC pipes offer thebest option. These are Horizontal Directional Drilling (HDD), Sliplining, Tight FitStructural Liner and Pipebursting. Table 1 summarizes the common trenchlessmethods, their applications, the reference specifications and the correspondingPVC pipe products that are available.Table 1: Construction/Rehabilitation Process and PVC SolutionsMethodApplicationStandarDASTM F 949SegmentalGravity Piping System RehabilitationASTM F 794Pressure Piping System RehabilitationAWWA C900/C905CSA B137.3ASTM D2241Horizontal DirectionalDrilling (HDD)New Pressure & GravityPiping System ConstructionAWWA C900/C905CSA B137.3ASTM D2241Pipe BurstingPressure & Gravity PipingSystem RehabilitationAWWA C900/C905CSA B137.3ASTM D2241Tight FitStructural LinerPressure & GravityPiping System RehabilitationAWWA C900/C905ASTM D2241ASTM F 1803SlipliningContinuousProducts utilize pipe that meet the referenced standard.

H O R I Z O N TA LDIRECTIONAL DRILLINGHorizontal directional drilling(HDD) is the most e.Traditionally these applicationswere reserved for only roadwayand river crossings. Today,Fig. 1a: Horizontal Directional Drilling (HDD) MethodHDD is employed for a myriadof other applications where the benefits of trenchless installation can be derived.In recent years, developments in the precision of HDD machinery, specificallythe ability to monitor and steer the pilot bore with high levels of accuracy thatmaintain line and grade, has also enabled the installation of gravity sewer pipes.HDD, Figure 1a, is performed with a drilling rig, Figure 1b, and involves threeFig. 1b: Horizontal DirectionalDrilling (HDD) Methodessential steps. First a pilot bore is created, covering the distance over which thepipe is to be installed. Highly sophisticated electronics enable the drilling rods tobe carefully guided and its direction of travel to be monitored. Reamers are thenpulled back to obtain a diameter large enough to accommodate the diameter ofthe pipe. Simultaneously, drilling mud is pumped into the bore to stabilize theboring and to prevent soil collapse. In the final step, the new pipe to be installedis pulled back through the bore, Figures c & d.Fig. 1d: Horizontal DirectionalDrilling (HDD) MethodFig. 1c: Horizontal Directional Drilling (HDD) Method

SLIPLININGSliplining is a processoutside diameter of the liner pipe isfor rehabilitating dete-less than the inside diameter of thehost pipe, which leaves an annularriorated large-diameterspace between the two. In many cases,gravity piping systemsthis annulus is filled with a grout afteror for the rehabilitatinginstallation, particularly if the hostof pressure distributionpipe is in a high state of deterioration.Grouting of the annular space providesand transmission lines.additional support for the liner pipe,helps protect the liner pipe if the hostSliplining involves thepipe is in structural distress, and stopsinsertion of a new pipewater infiltration through the hostinside the defectivehost pipe, either insegments or as a continuous section of pipe.Fig. 2b: Continuous Slipliningsectional area is often offset by thePVC slipliners are designed to provideboth structural support as well as animproved flow path to the deficienthost pipe, and have been in wide use innew PVC pipe.Continuoussliplining,Figure2b,with PVC pipe is more prevalent inSegmental sliplining, Figure 2a, is thedistribution and transmission pipelines.for gravity sewer lines. Profile-wall PVCpipe, conforming to ASTM gravity pipestandards, with smooth joints (bothinside and outside), are assembled insegments at entry points along thelength of the deteriorated host pipe,and inserted directly into the host pipeby either pulling or pushing. A sectionof the top half of the host pipe is oftencut off to provide lead-in access. The improved flow characteristics of theNorth America for over two decades.least disruptive type of rehabilitationFig. 2a: Segmented Slipliningpipe annulus space. The loss in cross-the rehabilitation of potable waterIn this process, the liner pipe, which ismanufactured to AWWA C900/C905and ASTM D2241 requirements, areassembled in their entirety prior tobeing pulled into the deterioratedhost pipe as a continuous pipeline.As with gravity systems, grouting ofthe annulus is often employed to helpstabilize the pipeline and increasethe life expectancy of the line. Whenrequired, taps are made after the pullin of the new pipe into the host pipe.

P I P E BU R S T I N GThe diameter of pipe being burstPipe bursting can betypically ranges from 2 to 30 inches,applied on a wide rangealthough pipes of larger diameters canof pipe sizes and typesbe burst. Pipe bursting is commonlyperformed size-for-size or one sizeand in a variety of soilupsize above the diameter of theand site conditions.existing pipe. Larger upsize (up tothree pipe sizes) has been successful,Fig. 3: Bursting Headbut the larger the pipe upsizing, the greater the force required to burst theexisting pipe and to pull the new pipe and the greater the potential for groundmovement (upheave).This is another rehabilitation method of replacing both pressure and gravitylines with new pipe and involves the breaking of an existing pipeline by brittlefracture, using mechanically applied force from within. While the deterioratedpipe fragments are forced into the surrounding ground, a new pipe of the same orlarger diameter is pulled in to replace the original pipe. Pipe bursting is performedby the insertion of a conically shaped bursting head, Figure 3, into a deterioratedpipe and causing it to shatter by pneumatic or hydraulic action, Figure 4.Fig. 4: Pipe Bursting

P V C P R E S S U R E P I P E S TA N D A R D SFOR TRENCHLESS CONSTRUCTIONPVC pressure pipes are routinely used for potable water distribution andtransmission, as well as in sanitary sewer force mains. The hydrostatic design basis(HDB) of PVC pressure pipe is the sustained hoop stress value from which theSpecific information onavailable wall thicknesslong-term pressure rating of the material is established. HDB is the starting pointfor determining the pressure capacity of a given wall thickness. AWWA and ASTMstandards for conventional PVC pressure pipe require an HDB of 4000 psi.and pressure classrating should be obtainedfrom manufacturers.Table 2: PVC Pressure Pipe Standards for Trenchless ConstructionStandardAvailable Diameters (in)Products utilizeAWWA C9004 - 12pipe that meet theAWWA C90514 - 48CSA B137.34 - 48ASTMD22412 - 24referenced standard.There are currently four PVC pressure pipe standards to which products fortrenchless technology are manufactured. Table 2 summarizes the size rangesavailable for each of these common standards. Pressure Ratings (and Classes) upto 315 psi are available for diameters up to 16 inches, 235 psi for diameters up to24 inches, and 165 psi for diameters up to 48 inches.

P V C G R AV I T Y P I P E S TA N D A R D SFOR TRENCHLESS CONSTRUCTIONProfile wall pipe generally fall into three categories – openNon-pressure PVC pipesprofile (OP), closed profile (CP), and dual wall corrugatedhave been in use in the U.S.since the early 1960s. Today,profile (DWCP). OP pipe have their rib-enforcementsPVC gravity pipe is used inexposed on the outside of the pipe and are manufactured tosanitary sewer, storm sewermeet the requirements of ASTM F794. CP pipe make use ofand highway drainage anda closed profile that provides a continuous outer wall whereculvert applications. Therethe wall sections are hollow and are often described as anare two main groups of PVCgravity pipe --- solid wallI-beam or honeycomb (refer to ASTM F1803). DWCP pipeand profile wall. For sliplin-have a smooth-wall waterway, braced circumferentially withing, only profile wall pipesan external corrugated wall (see ASTM F949 & F794).are utilized. There are threeprofile wall pipe standardsWhileallPVCpressurepipefor trenchless rehabilitation.is12454 and 12364 (minimum tensilemanufactured ONLY to cell classificationstrength of 6000 psi, minimum modulus12454 (tensile strength of 7000 psi,of elasticity of 440,000 psi). Pipe ASTM F794modulus of elasticity of 400,000 psi),manufactured to either formulationsome sewer pipe standards allowperforms ASTM F949manufacture of both cell classificationsapplications.verywellforsliplining ASTM F1803Table 3: ASTM Gravity PVC Pipe StandardsStandardSpecificationWall TypeASTM ementsCell ClassJoiningSystemsDWCPPipe Stiffness4” - 48”PS 4612454/12364GasketJointASTM F949DWCPPipe Stiffness4” - 36”PS 4612454GasketJointASTM F1803ClosedProfilePipe Stiffness18” - 60”PS 4612454/12364GasketJointD3034F679(D2241 andAWWA sizes)*Solid WallPipe Stiffness4” - 36”12454Gasket/ButtFusedJointsCross SectionPS46,115* Pressure Pipe