Technical Manual: Conduits through Embankment Dams (FEMA 484)

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Conduits through Embankment Damserosion severely damaged the partially constructed siphon. Temporary repairs wereunder way a few days later, but not yet completed, when another storm caused theembankment dam to again be overtopped. Erosion of the embankment dam, at thelocation of the siphon, by the second storm event caused the embankment dam tobreach.A decision was made to abandon the siphon spillway and instead construct aconcrete riser and barrel structure. However, the siphon was later repaired and wassuccessfully used to drain the reservoir (although several large pumps were alsorequired).Lessons learned (after Leumas, 1998)• A siphon may be an attractive option for providing an existing embankmentdam with a permanent means to drain a reservoir in lieu of excavation of theembankment to install a traditional bottom drain. However, many designelements should be considered in deciding whether to install a siphon, a lowlevel outlet works, or sliplining the existing deteriorated conduit. Each methodhas its own advantages and disadvantages. The long term performance of thefinal selection and public safety considerations, rather than cost, should be thebasis for the selected design.• Diversion during construction is a vital element to be considered in the designprocess. An acceptable level of risk for diversion requirements, which balanceseconomics for the project and an owner’s liability, must not compromise thesafety of the downstream public.• Bad weather can occur during any project. Contingency planning should bemade during the design process, which addresses what to do in the event thatthe capacity of diversion measures is exceeded. Such planning should have areadily available notification list of State dam safety program staff, emergencymanagement officials, and other State and local representatives, who can assistin the event of an emergency.ReferenceLeumas, James, To Siphon or Not To Siphon: That is the Question (Among Others)—ARepair History of the Crossgate Dam, 1998 ASDSO Annual Conference, Las Vegas,1998.B-38
Appendix B—Case HistoriesProject name: Dalewood Shores DamLocation: MississippiSummary: Man-entry inspection of a deteriorated corrugated metal outlet worksconduitDalewood Shores Dam was constructed in 1960 near Lauderdale, Mississippiwithout benefit of a qualified professional engineer. The 34-foot high embankmentdam has a crest length of 3,800 feet and impounds a surface area of roughly 1,000acres at normal pool elevation. Normal outflow occurs by way of a concrete chutespillway. Due to downstream development, the embankment dam is now classifiedas a high hazard structure.During construction, a 60-inch CMP conduit with an upstream flap gate wasinstalled through the embankment dam as a means to lower the reservoir level. Theflap gate failed the first time it was operated, and the owner abandoned the outletworks by covering the intake and gatewith soil and rock to prevent loss of thereservoir.Figure B-36.—A man-entry inspection ofthis 60-inch CMP noted seepage andextensive loss of embankment soil at twolocations.Subsequent sloughing of the upstreamslope damaged the upstream end of theCMP. An man-entry inspection of thepipe in 1993 noted that the pipe hadruptured, and seepage into the conduitwas observed at two locations. At thattime, the seepage flow was clear, and nosoil loss was evident. However, by 1995the seepage flow had increased, and soildeposits in the pipe indicated that internalerosion or backward erosion piping ofembankment material was occurring, andfailure of the embankment dam was adistinct possibility. Figure B-36 showsthe man-entry inspection beingperformed. Due to the potential for lossof life if the embankment dam were tofail, the State dam safety agency directedthe owner to hire a professional engineerto develop remedial plans to immediatelyrepair the dam.B-39
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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 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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Page 487 and 488: Appendix BCase HistoriesIndexDam Lo
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Appendix B—Case HistoriesProject
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Appendix B—Case HistoriesThe caus
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Appendix B—Case HistoriesFigure B
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Appendix B—Case HistoriesLessons
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Appendix B—Case Historiesof sever
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Appendix B—Case HistoriesLessons
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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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