Technical Manual: Conduits through Embankment Dams (FEMA 484)

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Conduits through Embankment DamsKey changes to the design that would likely have prevented embankment failureinclude:• Elimination of the antiseep collars• Utilizing a concrete encasement around the outlet conduit that allowed forbetter compaction of the earthfill against the conduit and to provide insulationduring cold weather• Lime treatment to stabilize the dispersive soils around the conduit• Utilizing a filter diaphragm with drainage provisions to the downstream toe• Provisions to stop the flow of cold air through the conduit during the winter• Provisions for slow first filling of the reservoirReferenceBureau of Land Management, Anita Reservoir (Blaine County, Montana) Dam Failure,Report by Board of Inquiry, August 20, 1997.B-4
Appendix B—Case HistoriesProject name: Annapolis Mall DamLocation: MarylandSummary: Forensic investigation of a spillway conduit failureIn March 1993, a newly constructed embankment dam near Annapolis, Maryland,rapidly filled with water during a storm and failed, causing extensive environmentaldamage, but no loss of life or damage to downstream roadways. Figure B-5 showsthe upstream section of the 54-inch diameter CMP spillway conduit, havingcompletely collapsed when the water level reached the elevation of the weirs on theinlet structure.The 25-foot high embankment dam, built in 1992 to manage stormwater runofffrom expansion of a nearby shopping mall, collapsed less than 1 year after it wasconstructed. Based on the original design drawings, the spillway inlet structure (riser)was a reinforced cast-in-place concrete box about 15 feet high and 10 feet square.The spillway conduit was 54-inch diameter CMP. The overall length of the conduitwas about 75 feet, and was to be constructed on a relatively steep slope of about10 percent. The first conduit joint was to be made within 2 feet of the riser. Fourcorrugated metal antiseep collars were to be installed on the conduit at distances ofFigure B-5.—The upstream section of the 54-inch diameter CMP spillwayconduit completely collapsed when the water level reached the elevationof the weirs on the inlet structure. Site personnel reported a “vortex” inthe pool adjacent to the structure shortly before collapse.B-5
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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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Page 459 and 460: GlossaryReferencesAmerican Concrete
Page 461 and 462: IndexAAbandonment of conduits, 225,
Page 463 and 464: IndexCompaction of backfill, 6, 10,
Page 465 and 466: IndexDDamembankment, 113-130, 333-3
Page 467 and 468: IndexExisting conduit, 23, 31, 45-5
Page 469 and 470: IndexHydraulic fracture, 4-11, 17,
Page 471 and 472: IndexMechanical caliper, 246Metal c
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Page 475 and 476: IndexSliplining, 39, 45-47, 51, 164
Page 477 and 478: IndexUUltrasonic pulse-echo, 245, 2
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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Appendix B—Case HistoriesFigure B
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Appendix B—Case HistoriesProject
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Appendix B—Case HistoriesLessons
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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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