Technical Manual: Conduits through Embankment Dams (FEMA 484)

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Conduits through Embankment DamsFigure 6.—Embankment dam failure caused by internal erosion of earthfillnear the conduit. The initial failure was tunnel shaped, but the collapse ofthe roof of the tunnel resulted in the observed shape of breach. Hydraulicfracture in highly dispersive clay embankment soils caused the failure. Theembankment dam design included antiseep collars, but no filter diaphragm.• Figure 7 illustrates the internal erosion process as a result of a hydraulic fracturethrough the embankment dam.• Figure 8 illustrates the internal erosion process as a result of low densityembankment materials under the haunches of a pipe due to poor compaction.• Figure 9 illustrates the internal erosion process associated with the creation of avoid caused by excessive compactive energy used to compact embankmentmaterials against the conduit.• Figure 10 shows the backward erosion piping process associated withintergranular seepage and the subsequent backward erosion of soil particles.All four of these mechanisms can lead to partial or full failures of the embankmentdam.Internal erosion and backward erosion piping can occur suddenly and with littlewarning. In these cases, little may be done to address the problem quickly enough toavert a failure. Recognizing conditions likely to result in these failure mechanisms isessential to design of conduits and embankment dams that are resistant to failures.In other cases, the failure mechanisms may develop slowly and go unrecognized untilthe subterranean erosion develops cavities in the embankment dam large enough to6
IntroductionAn embankment dam with a low reservoir water level.The reservoir water level rises, inducing a hydraulic fracture within theembankment dam due to poor construction or defective soils.The hydraulic fracture extends through the embankment dam as a result ofarching of the overlying embankment, resulting in low stress concentrations inthe soil and a reservoir level high enough to cause the fracture. Conduits oftencreate differential settlement and arching of the earthfill, because settlementof the embankment dam is less above the conduit than on either side of it.Figure 7.—The internal erosion process as a result of a hydraulic fracture.7
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
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Page 39 and 40: IntroductionConduits convey water f
Page 41 and 42: IntroductionFigure 3.—A 15-inch d
Page 43: Introductionunstable. When seepage
Page 47 and 48: A vortex may form at the location w
Page 49 and 50: IntroductionWater from the reservoi
Page 51 and 52: IntroductionFlowing water from the
Page 53 and 54: IntroductionThe process of dislodgi
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
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Page 91 and 92: 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 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 HistoriesThe caus
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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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