Technical Manual: Conduits through Embankment Dams (FEMA 484)

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Conduits through Embankment Dams• Loss of reservoir.—The reservoir is typically drained to provide upstream anddownstream access to the conduit.If the existing conduit has experienced significant deterioration or damage, furtherconsideration is required before proceeding with sliplining. Further considerationshould include:• Collapse.—If the existing conduit appears to be on the verge of collapse, thismay be an indication of considerable disturbance or movement of materialoutside of the conduit.• Seepage.—The greater the seepage flow, the more concern that the flow regimecould change considerably after sliplining, which could affect safety of theembankment dam. A change in the flow regime could force seepage to flowalong the exterior of the conduit. Any evidence that the seepage is underpressure from the reservoir head should be a consideration for replacement ofthe existing conduit in lieu of sliplining.• Location.—The location of any deterioration or damage within the existingconduit should be evaluated. Seepage upstream of a filter or impervious coremay not be as much of a concern as seepage downstream of these features.• Void.—If a void exists behind an opening in the existing conduit, the conduitshould probably be considered for removal and replacement. However, someconsideration should be given to where the void is located (near the intakestructure is less problematic than near the embankment dam centerline). If thevoid does not seem to be associated with much seepage flow, this could bemore of an indication that the void could be the result of erosive forces fromthe discharges through the existing conduit and that sliplining may be anoption. In some cases, it may be possible to fill the voids with grout. Slipliningof the existing conduit may not be economical, if extensive grouting of largevoids along the outside of the conduit will be required prior to inserting theHDPE slipliner. The costs involved should be compared to those required forremoval and replacement of the conduit.• Deterioration process.—If deterioration of the existing conduit is caused by acorrosive process, then the useful life expectancy of the existing conduit shouldbe evaluated based on the knowledge that deterioration will continue.Generally, the slipliner should be designed to accommodate all internal andexternal loadings without any support provided from the deteriorating conduit.If the existing conduit is expected to provide support for the new slipliner, andthe life expectancy of the existing conduit is less than the life of the project,then removal and replacement should be considered (figure 159).292
Chapter 12—Renovation of ConduitsFigure 159.—The holes in this CMP conduit were clearly visible afterremoval. The conduit was considered to be so severely corroded thatsliplining was not an option and it was removed and replaced. Photocourtesy of Maryland Dam Safety Division.12.1.1 ThermoplasticsThe guidance provided in section 12.1.1 mainly pertains to sliplining of inaccessibleconduits. The reader should understand that if the conduit is accessible by manentry,variance from this guidance will be required.The most commonly used thermoplastic for sliplining is smooth walled HDPE pipe.PVC pipe has been used in limited applications for sliplining, but has a number ofdisadvantages as discussed in section 2.2.1. For this reason, only HDPE pipe will bediscussed in this chapter. HDPE pipe used for sliplining should meet therequirements of ASTM D 2447, D 3035, and F 714.Additional design and construction guidance is available from other sources, such asCPChem’s The Performance Pipe Engineering Manual (2003), NRCS’s Structural Design ofFlexible Conduits (2005), Plastic Pipe Institute (PPI) Handbook of Polyethylene Pipe, andthe upcoming FEMA-sponsored “best practices” guidance document for plastic pipeused in dams (expected publication date, 2006).12.1.1.1 Design considerationsThe designer must evaluate a number of design parameters when considering HDPEpipe for use in sliplining. A few of the most significant design parameters include:• Seepage paths293
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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 13—Replacement of Conduit
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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 Historiespipe. Du
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Appendix B—Case HistoriesThe down
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Appendix B—Case HistoriesADownstr
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Technical Manual: Conduits through Embankment Dams (FEMA 484)

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