Technical Manual: Conduits through Embankment Dams (FEMA 484)

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Conduits through Embankment DamsBackward erosion piping begins in fine sand foundation materials at the toe ofan embankment dam. The foundation is assumed to be a soil susceptible topiping such as fine, poorly graded sand. A filter zone is not provided at theseepage discharge face (or the filter has been improperly designed), allowingbackward erosion piping to begin.Intergranular seepage flow conditions exist within the foundation under theembankment dam, and soil particles are removed. The particles are deposited(sand boils) on the ground surface at the downstream toe, or washed away ifflow is higher.Figure 10.—The backward erosion piping process associated with intergranular seepage andthe subsequent backward erosion of soil particles.14
IntroductionThe process of dislodging soil particles continues at an escalating rate becauseof the hydraulic gradient increase. As the backward erosion piping gets closerto the reservoir, seepage quantity also increases.A tunnel develops due to the continued erosion of the soils in the foundation.This assumes the overlying embankment dam, foundation layer, or conduit isable to support the tunnel that is forming. The soil exposed to flow in thedeveloping tunnel is erodible, and the walls of the tunnel can grow larger atthe same time that the discharge face moves upstream.Figure 10 (cont’d).—The backward erosion piping process associated with intergranularseepage and the subsequent backward erosion of soil particles.15
Page 1: Technical Manual:Conduits throughEm
Page 5 and 6: PrefaceTens of thousands of conduit
Page 7 and 8: Prefacecondition. The hazard classi
Page 9: PrefaceLakeLine MagazineMaryland Da
Page 16: Conduits through Embankment Dams11.
Page 19 and 20: Contents23 Precast concrete pipe be
Page 21 and 22: Contents81 On first filling, a high
Page 23 and 24: Contents117 This conduit was severe
Page 25 and 26: Contents158 An example of a histori
Page 27 and 28: ContentsFigures in the AppendicesNo
Page 29 and 30: ContentsB-33 Aerial view of Como Da
Page 31 and 32: ContentsB-81 Cross section of Wiste
Page 33 and 34: ContentsMASW, multichannel analysis
Page 35 and 36: Symbolsc, cohesionE', modulus of so
Page 37 and 38: ContentsD 3350D 4221D 4253D 4254D 4
Page 39 and 40: IntroductionConduits convey water f
Page 41 and 42: IntroductionFigure 3.—A 15-inch d
Page 43 and 44: Introductionunstable. When seepage
Page 45 and 46: IntroductionAn embankment dam with
Page 47 and 48: A vortex may form at the location w
Page 49 and 50: IntroductionWater from the reservoi
Page 51: IntroductionFlowing water from the
Page 55 and 56: Introductionbe observable at the su
Page 57 and 58: IntroductionFigure 11.—Example of
Page 59 and 60: Introductionwhere conduits were ass
Page 61 and 62: Introduction• Conduits within lev
Page 63 and 64: IntroductionFigure 12.—An example
Page 65 and 66: Introductionmore recent practiced h
Page 67 and 68: IntroductionThe “best practices
Page 69 and 70: Chapter 1GeneralConduits have been
Page 71 and 72: Chapter 1—GeneralFigure 14.—Ant
Page 73 and 74: Chapter 1—GeneralFigure 17.—Fai
Page 75 and 76: Chapter 1—Generalmeans the condui
Page 77 and 78: Chapter 1—Generalfacilitate futur
Page 79 and 80: Chapter 2Conduit MaterialsVarious m
Page 81 and 82: Chapter 2—Conduit MaterialsFigure
Page 85 and 86: Chapter 2—Conduit Materials• Co
Page 89 and 90: Chapter 2—Conduit MaterialsSteel
Page 91 and 92: Chapter 2—Conduit Materials2.3.2
Page 95 and 96: 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 Historieshistory
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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 Historiesinvert o
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Appendix B—Case Historiesdownstre
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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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