Technical Manual: Conduits through Embankment Dams (FEMA 484)

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Conduits through Embankment DamsEl. 485'2 21 12.75151Probable path of main leaks. Gradientis ≅ 10-15 feet/740 feet, or 1:60Figure B-81.—Cross section of Wister Dam showing probable path forinternal erosion through embankment. The length of the flow path wasabout 740 feet, and the head on the entrance tunnels was less than15 feet.extensive grouting, a steel sheet pile wall, and additional upstream and downstreamberms and drains. After completion of the remedial work, the embankment dam hasbeen in operation continuously with little trouble. A major renovation program wasfinished in 1990. The renovation included a slurry panel wall installed for the fullheight of the embankment.Sherard concluded that the cause of the leakage path in the embankment dam couldonly be attributed to hydraulic fracture in the embankment. The flow pathdeveloped immediately above the closure section on the embankment dam, also justabove the old stream channel. Aggravating this condition was the fact that the rightbank of the stream channel (viewed downstream) consisted of a bedrock shelf thatcontributed to differential settlement. A plan view of the area of the leak is shown infigure B-82. A longitudinal profile of the area where the leak developed is shown asfigure B-83. Note that this view is looking upstream.The embankment dam was compacted to a relatively high dry density correspondingto about 97 percent of the maximum Standard Proctor dry density, and it wascompacted at about optimum water content. The soils were silty, relatively low inplasticity, and highly dispersive. Compaction at these conditions probably resulted ina somewhat brittle fill likely to crack when subjected to differential settlement.Lessons learnedThe incident demonstrated that even well constructed embankment dams built bywhat was then state-of-the-art technology are susceptible to hydraulic fracture andinternal erosion if they are not protected by internal chimney filters. Modernembankment dam design concepts include protective filters for all significant andhigh hazard embankment dams, and even low hazard dams if constructed ofB-118
Appendix B—Case HistoriesADownstream toeUpstream toePoteau RiverDirection of major leaksAFigure B-82.—Plan View of Wister Dam showing flowpath for internal erosion tunnels in fill.Top of dam El. 527.5'Probable arching in closure sectionProbable location of major leaksRiver channelFoundation alluviumShale bedrockFigure B-83.—Cross section A-A from figure B-82. Profilealong centerline of embankment viewed upstream.problematic soils, such as dispersive clays. This case history also illustrates theincreased potential for arching and hydraulic fracture associated with closure sectionsin embankment dams.ReferencesCasagrande, Arthur, Notes on the Design of Earth Dams, Journal of the Boston Society of CivilEngineers, October, 1950, pp. 231-255.Rutledge, Philip, and James P. Gould, Embankment Dam Cracking, CasagrandeVolume, John Wiley and Sons, New York, 1973, pp. 272-353.B-119
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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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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 HistoriesLessons
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Appendix B—Case Historiespipe. Du
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Appendix B—Case Historiesinvert o
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Technical Manual: Conduits through Embankment Dams (FEMA 484)

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