Technical Manual: Conduits through Embankment Dams (FEMA 484)

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Conduits through Embankment DamsFigure 80.—Mastic being applied to exterior annular joint space ofprecast concrete pipe.• Water or air pressure testing the completed conduit to approximately 10 feet ofhydrostatic head is highly recommended before casting the cradle.An alternative to gasketed joints in PCCP (lined-cylinder, AWWA C301) is weldedjoints (also known as internal welded tied joints). Welded joints have been used inwater pipelines to form a watertight barrier for about 30 years. A continuous interiorside fillet weld is required to provide the watertight seal. Typically, the rubber gasketis not installed in the spigot groove, since the gasket would burn during the weldingoperations. Welded joints should only be used for conduit diameters of 36 inches orlarger to accommodate access by man entry. The designer will need to carefullyevaluate if this alternative provides adequate watertightness for the given conduitapplication.112
Chapter 5Foundation and Embankment DamPrevious chapters have discussed the importance of placing the conduit in the mostfavorable location within the embankment dam to reduce problems with foundationand embankment settlement. In this chapter, the reactions of soil and rockfoundation horizons and how they can affect the design of the conduit are discussed.If conduits are located on foundations that are not uniform, differential settlementcan lead to cracking and joint problems in the conduit. If foundations consist of lowstrength or highly compressible materials, unacceptable deformations and lateralmovements can damage the conduit.Other discussions in this chapter address how the settlement of embankments nearconduits can create hydraulic fracture mechanisms. Design approaches effective inpreventing this problem are included. The importance of careful design ofexcavations made to install conduits is extensively discussed. Special attention isrecommended for any excavations made transverse to the centerline of theembankment where the excavation backfill may be different in compressibility thanthe adjacent foundation materials. Recommendations for backfilling soils nearconduits are provided. Problematic soils, such as broadly graded soils and dispersiveclays are defined, and potential problems associated with them are also discussed.5.1 Excavation and foundation preparationIdeally, sound rock provides the best foundation conditions for conduits. However,ideal conditions are rare, and many embankment dam sites have marginal foundationconditions.If the underlying foundation is highly compressible, subject to collapse uponsaturation, or has other objectionable properties, the conduit could be damaged fromexcessive settlement. In some cases, unsuitable foundation soils must be removedand replaced to prevent damage to the conduit. Backfill used in excavations forconduits must be compacted uniformly under the conduit. Excavations should bewide enough to accommodate motorized compaction equipment. The side slopes ofthe excavation must be flat enough to avoid differential settlement of theembankment dam near the conduit.113
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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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Page 195 and 196: 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 10—Evaluation by Geophysi
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Chapter 11Appropriate Emergency Act
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Chapter 11—Appropriate Emergency
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Table 11.2.—Potential problems an
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Chapter 12Renovation of ConduitsThe
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Chapter 12—Renovation of Conduits
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Chapter 13Replacement of ConduitsGe
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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 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 Historiesarea, a
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Appendix B—Case Historiespipe. Du
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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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