Technical Manual: Conduits through Embankment Dams (FEMA 484)

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Conduits through Embankment DamsAfter the HDPE slipliner is placed within the existing conduit, time should beprovided for its temperature to equalize prior to grouting. Typically, 24 to 48 hoursshould be adequate. However, the designer should use their own judgement andallow for additional equalizing time when installations occur during periods ofextreme temperatures. Circulating water in the slipliner can assist with thetemperature equalization process. Nighttime installation may be another option toconsider to reduce the effects of extreme temperature.The use of upstream and downstream end restraints on the HDPE slipliner will limitexpansion/contraction. Once the HDPE slipliner is grouted in place, it shouldundergo little expansion/contraction. This is largely due to the low modulus ofelasticity of the HDPE pipe. The HDPE slipliner may try to expand, but in arestrained condition it cannot mobilize forces of the magnitudes required to causeexpansion movement. Since HDPE pipe does not bond with the grout, the resistiveforces are largely from the friction along the HDPE pipe/grout interface. Therefore,thrust-accommodating end structures are generally not required for HDPE sliplinedconduits.Stress cracking.—HDPE pipe failures are often attributed to the effects ofenvironmental stress cracking (also called slow crack growth). This phenomenoncan occur during the handling or installation of HDPE pipe. The HDPE pipe couldbe gouged, scratched, or kinked, resulting in a weak spot on the pipe wall.Subsequent operations of grouting the HDPE pipe or pressurizing the conduit resultcracking of the weakened section. Specifying HDPE pipe made with ASTM D 3350cell classification 345464C grade resin provides the highest level of resistance to slowgrowth cracking and can negate the possibility of this type of failure. This ensures avirgin, high-grade, very stiff resin which has been found highly resistant toenvironmental stress cracking. Other grades of resin often contain some percentageof low-grade recycled resins.Joints.—The most common method used to join HDPE pipe is heat fusion (ASTMD 2657). This method is also known as butt fusion. The butt fusion technique is awidely used and industry-accepted heat fusion method for joining sections of smoothsolid walled HDPE pipe. This method produces a joint that is watertight and is asstrong or stronger than the HDPE pipe material itself, if performed correctly. Aspecial machine (figure 163) is used to trim the ends of the pipes (facing or squaringoff), align the ends of the pipe, heat both ends of the pipes to about 400 to 450 °F,and force the ends together under pressure. The melt bead size required for thethickness and diameter of the HDPE pipe determines how much pressure and timeis needed for fusion of the joint. About 1 hour should be allowed for the joint toadequately cool after completion of the fusion process (figure 164). Trial fusionsshould be considered at the beginning of the day, so the fusion procedure andequipment settings can be verified for the actual jobsite conditions. Manufacturer’srecommended procedures should always be observed for heat fusion.298
Chapter 12—Renovation of ConduitsFigure 163.—HDPE pipe joint being fusion welded.A small bead (figure 165) is formed where the meltedmaterial is extruded from the joint. Beads appear onboth the inside and the outside of the HDPE pipe.The need for bead removal is uncommon, but can beaccomplished using special tools after the joint hasthroughly cooled to ambient temperature. If removalis necessary, the personnel using the debeading toolshould be properly trained, so the HDPE pipe is notneedlessly gouged. The existence of the interior beadhas a negligible impact on the hydraulic performanceof the slipliner. A bead exists on the exterior surfaceof the joint. If proper annulus clearance is provided bythe designer, this should not affect slipliner insertion orthe grouting process. The beads should be throughlyinspected for uniformity and proper sizearound the entire joint. Visual inspection isusually adequate; however other methods, suchas radiographic or ultrasonic methods, can beused. The use of fusion machine operatorswho are skilled, knowledgeable, and certified bythe manufacturer will produce a good qualityjoint. Improperly heat fused joints cannot berepaired and must be cut out, and the endsFigure 164.—Finished fusionwelded joint.Figure 165.—Interior view offinished joint bead.299
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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 10Evaluation by Geophysical
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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 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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