Technical Manual: Conduits through Embankment Dams (FEMA 484)

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Conduits through Embankment Dams• Service life• Initial inspection of the existing conduit• Selection of the diameter and thickness• Thermal expansion/contraction• Stress cracking• Joints• Flotation• Entrance and terminal structuresThese parameters are further discussed in the following paragraphs. On a case-bycasebasis, the designer may need to consider additional parameters depending onthe performance criteria and design requirements of the specific application.Seepage paths.—When an HDPE slipliner installation eliminates seepage into theconduit, the flow patterns within the surrounding embankment are changed andother undesirable seepage paths may develop. Any existing seepage paths mayexperience an increase in flow. For instance, if an existing deteriorated conduit hasacted as a drain and reduced the phreatic surface within the embankment dam, thephreatic surface may increase and force flow through the dam, (along the exterior ofthe existing conduit) after slipliner installation. This seepage and the potential forinternal erosion or backward erosion piping along the conduit must be addressed byinstalling a filter diaphragm or collar at the downstream end of the existing conduit.The filter diaphragm or collar should be designed to prevent migration of the fines inthe embankment dam and should be placed around the entire circumference of theexisting conduit. For guidance on the design and construction of the filters, seechapter 6.Service life.—The service life for HDPE pipe is a function of the stress history ofthe pipe. A typical design calls for a 50- to 100-year service life.Initial inspection of the existing conduit.—A thorough inspection of the existingconduit is required prior to selecting the diameter of the HDPE slipliner.Depending on the diameter of the existing conduit, man-entry or CCTV inspectionmethods should be used; see section 9.5.2 for guidance on inspection of conduits.The condition of the existing conduit, existence of any protrusions or obstructions,joint offsets, amount of deflection, and evidence of leakage or movement ofembankment materials should be determined. The existence of any deflections,294
Chapter 12—Renovation of Conduitsprotrusions, or irregularities in the existing conduit will control the selection of theslipliner diameter. The pulling or pushing of a template (figures 160 and 161),inflatable pipeline sphere, or soft (typically open cell polyurethane foam) pig(figure 162) through the existing conduit is recommended. This will also ensure thatsliplining can be done without difficulty.Selection of the diameter and thickness.—The selection of the diameter andthickness of the HDPE slipliner should consider the following factors:• Size and condition of the existing conduit.—The size of the existing conduit limits thediameter of the HDPE slipliner. Further, if the existing conduit has anyprotrusions or obstructions (i.e., deflection, joint offsets), the diameter of theHDPE slipliner may need to be made smaller to accommodate theserestrictions.• Discharge requirements.—At maximum full open operation, the HDPE sliplinershould not flow greater than 75 percent full (i.e., 75 percent of the insidediameter) at the downstream end, to minimize the risk of surging or pressureflow developing in the conduit. Pressurized HDPE slipliners are notrecommended for significant and high hazard embankment dams. However, analternative to single wall HDPE pipe is available. This involves the use of adual wall containment pipe; see the discussion later in this section for furtherinformation.HDPE pipe is very smooth. While the insertion of a new HDPE sliplinerresults in a smaller flow area, the reduced friction of the water passing throughthe slipliner results in only minimal losses of hydraulic capacity, if any.Typically, a new, smaller diameter HDPE slipliner has a hydraulic capacity equalto or greater than the original conduit. For example, the Manning’s “n” valuefor smooth walled HDPE pipe is 0.009, compared to 0.010 for steel, 0.013 forconcrete, and 0.022 for CMP.• Clearance requirements for grouting of the annulus between the existing conduit and theHDPE slipliner.—To maintain sufficient clearance during the sliplining process,the outside diameter of the slipliner should be at least 10 percent smaller thanthe inside diameter of the existing conduit (ASTM F 585). This clear dimensionbetween the interior surface of the existing conduit and outside surface of theslipliner allows for problem-free installation and grouting of the annular space.The designer needs to verify that the clear dimension will accommodate groutand vent pipes, when selecting the outside diameter of the HDPE slipliner.• Internal and external loadings.—Conservatively, the HDPE slipliner should bedesigned with the assumption that the existing pipe continues to deteriorateafter renovation is completed and will provide no support. For this reason, the295
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Technical Manual:Conduits throughEm
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PrefaceTens of thousands of conduit
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Prefacecondition. The hazard classi
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PrefaceLakeLine MagazineMaryland Da
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Conduits through Embankment Dams11.
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Contents23 Precast concrete pipe be
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Contents81 On first filling, a high
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Contents117 This conduit was severe
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Contents158 An example of a histori
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ContentsFigures in the AppendicesNo
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ContentsB-33 Aerial view of Como Da
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ContentsB-81 Cross section of Wiste
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ContentsMASW, multichannel analysis
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Symbolsc, cohesionE', modulus of so
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ContentsD 3350D 4221D 4253D 4254D 4
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IntroductionConduits convey water f
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IntroductionFigure 3.—A 15-inch d
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Introductionunstable. When seepage
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IntroductionAn embankment dam with
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A vortex may form at the location w
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IntroductionWater from the reservoi
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IntroductionFlowing water from the
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IntroductionThe process of dislodgi
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Introductionbe observable at the su
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IntroductionFigure 11.—Example of
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Introductionwhere conduits were ass
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Introduction• Conduits within lev
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IntroductionFigure 12.—An example
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Introductionmore recent practiced h
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IntroductionThe “best practices
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Chapter 1GeneralConduits have been
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Chapter 1—GeneralFigure 14.—Ant
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Chapter 1—GeneralFigure 17.—Fai
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Chapter 1—Generalmeans the condui
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Chapter 1—Generalfacilitate futur
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Chapter 2Conduit MaterialsVarious m
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Chapter 2—Conduit MaterialsFigure
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Chapter 2—Conduit Materials• Co
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Chapter 2—Conduit MaterialsSteel
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Chapter 2—Conduit Materials2.3.2
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Chapter 3Hydraulic Design of Condui
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Chapter 3—Hydraulic Design of Con
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Chapter 4Structural Design of Condu
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Chapter 4—Structural Design of Co
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Chapter 5Foundation and Embankment
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Chapter 5—Foundation and Embankme
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Chapter 6Filter ZonesZones of desig
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Chapter 6—Filter Zonesseepage or
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Chapter 6—Filter ZonesFigure 87.
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Chapter 6—Filter Zones3. Upstream
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Chapter 6—Filter Zonesbedrock sur
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Chapter 6—Filter Zoneszones, and
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Chapter 6—Filter Zonesfiltering t
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Chapter 6—Filter Zonessoil. This
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Chapter 6—Filter Zones6.8 Specifi
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Chapter 6—Filter ZonesVarious deg
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Chapter 6—Filter Zones• For pre
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Chapter 7Potential Failure Modes As
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Chapter 7—Potential Failure Modes
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Chapter 8Potential Defects Associat
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Chapter 8—Potential Defects Assoc
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Chapter 9Inspection and Assessment
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Chapter 9—Inspection and Assessme
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Chapter 14Repair and Abandonment of
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Chapter 14—Repair and Abandonment
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ReferencesThe following references
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ReferencesBureau of Reclamation, De
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ReferencesCooper, Chuck, E. Wesley
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ReferencesJacobsen, S., “Buckling
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ReferencesNatural Resources Conserv
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ReferencesU.S. Army Corps of Engine
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ReferencesWooten, R. Lee, Peter S.
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Additional ReadingThe following ref
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Additional ReadingCarter, Brent H.,
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Additional ReadingJohnson, Brian, J
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Additional ReadingNatural Resources
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Additional ReadingU.S. Army Corps o
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Additional ReadingVan Aller, Hal, R
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GlossaryThe terms defined in this g
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Glossary• Backward erosion piping
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GlossaryCathodic protection system
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GlossaryConsequences (FEMA, 2004):
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Glossarymalfunction or abnormality
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GlossaryDrawdown (FEMA, 2004): The
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GlossaryFailure mode (FEMA, 2004):
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GlossaryGate chamber: An outlet wor
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GlossaryImpervious: Not permeable;
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GlossaryLeakage (FEMA, 2004): Uncon
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GlossaryOpen cut: An excavation thr
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GlossaryPolyvinyl chloride (PVC): A
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GlossaryResistivity: A measure of t
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GlossarySettlement (FEMA, 2004): Th
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GlossaryStandard Proctor compaction
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GlossaryThermoset (ASTM F 412, 2001
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GlossaryReferencesAmerican Concrete
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IndexAAbandonment of conduits, 225,
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IndexCompaction of backfill, 6, 10,
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IndexDDamembankment, 113-130, 333-3
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IndexExisting conduit, 23, 31, 45-5
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IndexHydraulic fracture, 4-11, 17,
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IndexMechanical caliper, 246Metal c
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IndexPressure flow, see Conduit, pr
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IndexSliplining, 39, 45-47, 51, 164
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IndexUUltrasonic pulse-echo, 245, 2
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Appendix AHistory of Antiseep Colla
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Appendix A—History of Antiseep Co
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Appendix BCase HistoriesIndexDam Lo
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Appendix B—Case HistoriesDam Loca
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Appendix B—Case HistoriesProject
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Appendix B—Case HistoriesFigure B
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Appendix B—Case Historiesproject,
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Appendix B—Case Historieswatersto
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Appendix B—Case HistoriesLessons
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Appendix B—Case HistoriesThe cond
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Appendix B—Case Historiesroadway.
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Appendix B—Case Historiesentire c
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Appendix B—Case Historieshauled i
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Appendix B—Case Historiescoal tar
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Appendix B—Case Historieshistory
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Appendix B—Case Historiesarea, a
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Appendix B—Case Historiespipe. Du
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Appendix B—Case Historiesinvert o
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Appendix B—Case Historiesof sever
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Appendix B—Case HistoriesThe down
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Appendix B—Case Historieshose and
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Appendix B—Case HistoriesADownstr
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Technical Manual: Conduits through Embankment Dams (FEMA 484)

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