Technical Manual: Conduits through Embankment Dams (FEMA 484)

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Conduits through Embankment Damsfor loss of structural strength over time. Water tests were performed to determine ifthe water in the reservoir and the conduit were acidic or contained anything thatwould be detrimental to the concrete. The water tests results were negative, and itwas concluded that the condition of the concrete could be a result of poorconsolidation and possibly other poor construction practices.The upstream conduit had never been inspected, since the reservoir would need tobe drawn down to the level of the intake structure. In lieu of reservoir drawdown,an underwater inspection was performed in September 2001 to assess the conditionof the concrete. The divers found the concrete in the intake structure to be in verygood condition with no signs of deterioration. The concrete in the upstream conduitdid not appear to be in as good of condition as the intake structure. The diversinspected and videotaped approximately 80 linear feet of the conduit. A knife wasused to probe cracks and deteriorated areas in the concrete. Figure B-73 shows thediver using a knife to probe a crack in the conduit. In general, the crown of theupstream conduit was in the best condition, with most of the concrete being smoothand free of voids. The floor of the conduit is mostly smooth to 1 /8-inch relief. Thesides of the conduit were in the poorest condition with concrete relief being 1 /8 to1/4 inch thick with localized areas to 3 /4 inch thick. Some areas of unconsolidatedconcrete were observed on the sides of the upstream conduit, but did not appear tobe as severe as what was observed on the downstream conduit. The divers alsoinspected the upstream sides of the two 3-foot by 4-foot 6-inch cast-iron slide gates.During the inspection, the divers took care not to stir up particles on the invert, toavoid reducing the water visibility to near zero.Due to the poor condition of the concrete within the downstream conduit and voidson the outside of the conduit, a decision was made to perform outlet worksmodifications to mitigate the existing dam safety deficiencies. In 2003, a 48-inchinside diameter steel liner was installed, and the annulus between the steel liner andexisting concrete conduit was backfill grouted. As part of the outlet worksmodifications, a filter collar was installed around the downstream end of the conduit.The upstream conduit was determined to be of adequate condition to continue inservice without repair, but underwater inspection should be made at regular 6-yearintervals.Lessons learned• Man-entry inspection should be used to evaluate the condition of the conduitfor both temporary repairs and permanent renovations.• Where feasible, divers should be used to perform underwater inspections ofconduits that cannot be dewatered.B-96
Appendix B—Case HistoriesFigure B-73.—The diver used a knife to probe cracks in the concrete.Divers prefer knives with blunt ends in underwater inspection, since it isless likely that a hole could accidently be poked into their dry suits.ReferenceBureau of Reclamation, Report of Findings—Spillway and Outlet Works ConduitModifications—Corrective Action Alternatives, February 7, 2002.Bureau of Reclamation, Design Summary—Salmon Lake Dam Modifications, OkanoganProject, Washington, October 2003.B-97
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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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Technical Manual: Conduits through Embankment Dams (FEMA 484)

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