Technical Manual: Conduits through Embankment Dams (FEMA 484)

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Conduits through Embankment DamsProject name: Como DamLocation: MontanaSummary: Sliplining of an existing outlet works conduit using a steel pipe sliplinerComo Dam was constructed by semihydraulic fill method from 1908 to 1910.Como Dam has a crest length of 2,550 feet and a crest width of 25 feet. Thestructural height is 70 feet, and the base width is 400 feet. The spillway wasconstructed in 1923 and is located on the left abutment. The outlet works conduitthrough the embankment dam was a 6-foot inside diameter, 526-foot longconcrete-encased redwood stave pipe. The wood staves in the pipe are 3 inchesthick. Approximately half of the downstream conduit was relined in 1936 with3/8-inch thick steel plate liner. Figure B-33 shows an aerial view of Como Dam.The reservoir was maintained at a reduced level, because increased seepage throughthe embankment dam during the summer of 1992 caused concern over the safety ofthe dam. An emergency situation was declared, which required modification to theembankment dam and appurtenances to be completed in the fall of 1992 and winterof 1993 to allow operation of the reservoir in the spring. An original plan includedreplacing 130 feet of the downstream conduit, since the embankment above the pipehad to be removed and replaced. However, this was not feasible because of timerestrictions. Potential seepage through the concrete in some areas of the pipe andthe deteriorated condition of the redwood liner plates led to the plan to line theB-34Figure B-33.—Aerial view of Como Dam, Montana.
Appendix B—Case Historiesentire conduit with a steel pipe slipliner. This steel pipe slipliner would provideadditional structural stability and a good flow surface, prevent seepage through theconcrete, and could be placed in an expeditious manner to allow reservoir operationin the spring of 1993.The existing redwood liner was removed from the inside of the concrete conduit,upstream and downstream of the gate chamber. A 66-inch diameter steel pipeslipliner (figure B-34) was placed inside the existing concrete conduit, upstream anddownstream of the gate chamber. The steel pipe slipliner was placed in 20-footsections. These sections were pulled into place, and the ends were butt strapped andwelded. The voids between the steel pipe slipliner and the concrete conduit werethen grouted through grout plugs in the steel pipe slipliner. This work (about300 feet of pipe) was completed in about 1 month. A new transition structure wasplaced between the conduit and the terminal structure. Also, the exit channel wasmodified by placing grouted riprap for about 150 feet downstream of the terminalstructure.Lessons learnedRapid installation of a steel pipe slipliner can be done to facilitate reservoiroperations.Figure B-34.—Installing the steel pipe slipliner within the existing outletworks conduit.B-35
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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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Page 479 and 480: Appendix AHistory of Antiseep Colla
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Page 487 and 488: Appendix BCase HistoriesIndexDam Lo
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Page 543 and 544: Appendix B—Case Historieshistory
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Page 559 and 560: Appendix B—Case Historiesinvert o
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Appendix B—Case HistoriesFigure B
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Appendix B—Case HistoriesProject
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Appendix B—Case HistoriesThe caus
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Appendix B—Case HistoriesLessons
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Appendix B—Case Historiesof sever
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Appendix B—Case HistoriesLessons
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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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