Technical Manual: Conduits through Embankment Dams (FEMA 484)

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Conduits through Embankment Damsmaterial characteristics indicate adequate protection against internalerosion and backward erosion piping.6. Whatever conduit installation method is to be used, the specificationsshould include a detailed step-by-step procedure for installing the conduitand for achieving full contact with the bedding and backfill. The type ofequipment to be used to achieve the specified backfill densities should bespecified. Quality control during construction should be the responsibilityof a registered professional engineer who is familiar with the projectspecifications and the potential problems. The specifications shouldindicate how it will be determined that full contact between the conduitand the backfill has been achieved and the required backfillmoisture/density specifications have been met. The engineer should berequired to inspect and accept the conduit bedding and backfill before thebackfill is placed over the conduit.Even though these dams differ significantly from embankment type dams, theycan experience failure. Regulatory agencies, dam owners, and designers mayfind application of the guidance provided in this document can improve theoverall integrity of their structure. They should fully consider the basis forthese best practices and decide on the applicable guidance to use. Where thedesign and construction of a conduit through these types of dams deviates fromthese best practices, the designer should ensure that potential problems areotherwise accounted for in the design.30
Chapter 1GeneralConduits have been placed through embankments for centuries. However, placing aconduit within an embankment dam increases the potential for seepage and internalerosion or backward erosion piping. Water may seep through the earthfillsurrounding the conduit, through cracks in the embankment caused by the conduit,or into or out of defects (e.g., cracks, deterioration, or separated joints) in theconduit. If the conduit is flowing under pressure, and defects exist in the conduit,the water escaping the conduit can erode surrounding soils.Replacement of a conduit through an embankment dam is difficult, time consuming,and expensive. Designers should adopt a conservative approach for the design ofconduits. The purpose of this chapter is to provide guidance for both constructingnew conduits and renovating or replacing existing conduits in embankment dams.When evaluating existing conduits, designers should attempt to determine howclosely the design of the existing conduit complies with criteria for new conduits. Ifthe existing conduit lacks state-of-the-practice defensive design measures, it may beconsidered inadequate by modern standards. These design measures should provideboth primary and secondary defensive measures to reduce the probability of failures.Inadequate conduit designs, poor construction, and improper maintenance canadversely affect the safety of embankment dams.1.1 Historical perspectiveMost designers of embankment dams have attempted to include defensive designmeasures to address potential seepage along conduits extending through earthfill orearth- and rockfill embankments. Even so, many observed failures and accidents ofembankment dams have occurred, involving conduits or the earthfill near theconduits. For large embankment dams, about one-half of all failures are due tointernal erosion or backward erosion piping. In about one-half of these failures,internal erosion or backward erosion piping was known to have initiated around ornear a conduit (Foster, Fell, and Spannagle, 2000, p. 1032). This means that about25 percent of all embankment dam failures are a result of internal erosion orbackward erosion piping associated with conduits.31
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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.
Page 19 and 20: Contents23 Precast concrete pipe be
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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
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Page 31 and 32: ContentsB-81 Cross section of Wiste
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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
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Page 49 and 50: IntroductionWater from the reservoi
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Page 53 and 54: IntroductionThe process of dislodgi
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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: IntroductionThe “best practices
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Page 73 and 74: Chapter 1—GeneralFigure 17.—Fai
Page 75 and 76: Chapter 1—Generalmeans the condui
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Page 79 and 80: Chapter 2Conduit MaterialsVarious m
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Page 95 and 96: Chapter 3Hydraulic Design of Condui
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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 Historiespipe. Du
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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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