Technical Manual: Conduits through Embankment Dams (FEMA 484)

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Conduits through Embankment Dams1982. Operational history and performance of the feature, since its previousinspection.3. Relative costs for providing access for inspection of the feature, includingcosts associated with lost water and power revenues.4. Age of the feature.5. Design and construction considerations, such as:a. Changes in standards or guidelines.—Design criteria, constructiontechniques, and/or quality of material at the time of construction failto meet current standards or guidelines.b. Foundation conditions.—The conduit was constructed on foundation ofvarying compressibility, where there is a potential for differentialsettlement. This may result in cracking of the conduit or excessiveopening of joints. Differential settlement is also possible betweenthe conduit and gate chamber due to different pressures beingexerted on them.c. Foundation faults.—The conduit crosses a foundation fault where thereis the potential for movement or disruption of the conduit.d. Unfavorable stresses.—The conduit is located where conditions areconducive to arching, resulting in unfavorable stresses in theembankment dam and/or conduit. These stresses could beconducive to hydraulic fracture of the embankment dam or stressconcentrations on the conduit.e. Conduit within the core of the embankment dam.—A significant portion ofthe conduit upstream from the gate chamber lies within the core ofthe embankment dam, so that any cracks in the conduit create thepotential for water to be injected under pressure into the core. Iferodible material is used to construct the impervious core, thepotential for adverse consequences is increased.f. Inadequate conduit joints.—Inadequately sealed or encased conduitjoints, which could lead to the escape of water under pressure, whichcreates the potential for water to be injected under pressure into thesurrounding embankment.g. Filters.—Lack of adequate filters and drainage material around theconduit downstream from the im pervious zone of the embankment
Chapter 9—Inspection and Assessment of Conduit-Related Problemsdam to safely convey seepage or leakage along the conduit to an exitpoint.6. Critical function of the feature.7. Any existing site conditions that may compromise the safety of the feature.The appropriate frequency and extent to which the normally inundated featuresare examined will vary based on available information. The review personneland decisionmakers will need to determine the appropriate frequency andextent based on the above factors. As an example, Reclamation has identifiedabout 6 years as an appropriate frequency for a “hands-on or equivalentinspection frequency” for inaccessible features, such as conduit.• Operation.—Certain problems may not normally appear when the feature is drythat appear when the feature is being operated. Also, when a feature isoperating during a period of higher than normal releases, additional informationmay be gathered that may not have been available during normal operations.The opportunity to optimize both access and operation during a single inspectiontypically is not possible. Inspection objectives may have to alternate from oneinspection to the next. This may necessitate the need for scheduling “special”inspections during unusual conditions, in addition to regular inspections to provide acomprehensive understanding of the conduit safety. Special inspections may berequired after floods, seismic activity, or other unusual or extreme events.9.3 Periodic inspections by selected organizationsThe frequency of periodic inspections varies among organization and embankmentdam owners. Emergency situations may require much more frequent inspections,such as daily or hourly. Situations can arise suddenly that cause serious damage in ashort period of time. Examples of these problems are operations at full dischargecapacity, seismic activity, or other special conditions. The need for specialinspections should be evaluated after occurrence of any of these situations.A sampling of periodic inspections as required by selected organizations:• Reclamation.—Reclamation employs the following process (Reclamation, 1998c,pp. 2-11) to monitor its significant and high hazard dams and attempt to detectany potential dam safety deficiencies:1. Annually.—Annual inspections are performed by inspectors who aregeneralist (as opposed to specialist) engineers very familiar with the199
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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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Page 195 and 196: Chapter 7Potential Failure Modes As
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Page 215 and 216: Chapter 8Potential Defects Associat
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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 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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