Technical Manual: Conduits through Embankment Dams (FEMA 484)

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Conduits through Embankment DamsProject name: Loveton Farms DamLocation: MarylandSummary: Failure of an embankment dam by internal erosion along the spillwayconduitLoveton Farms Dam is a 23-foot high earth embankment dam in Baltimore County,Maryland. The dam was constructed in 1985 as a stormwater management structureto attenuate increased runoff due to commercial and residential development of thewatershed. The embankment dam is a “dry structure” which does not normallyimpound any water. The spillway consists of large diameter (78-inch diameter) CMPconstructed through the embankment dam. A vertical section of CMP about 16 feethigh (riser) was constructed at the upstream end of the spillway pipe. Low flowspass through a small (1-foot) opening at the base of the riser. Flows in excess of the100-year storm bypass the embankment dam via an emergency spillway channelexcavated in the left abutment.The embankment dam is essentially a homogeneous embankment constructed oflocal residual soils. These soils are micaceous silty fine sands and sandy siltsweathered from the parent rock (Piedmont Geologic Province). They are classifiedas SM and ML under the Unified Soil Classification System. Typical liquid limits areabout 30 percent, with a plasticity index of about 7.The embankment dam failed less than a year after it was completed, when a relativelysmall storm filled the pool to the top of the riser. Failure was attributed to internalerosion of embankment fill along the outside of the pipe (figures B-50 and 51). Theoriginal spillway pipe was likely placed in a vertically sided trench excavated throughthe nearly completed embankment dam. This construction technique is notrecommended, as it makes compaction of the soil under the sides of pipe verydifficult.Poorly compacted fill in this area results in poor support of the pipe, which causesexcessive deformation of the pipe and may cause the joints to separate. In addition,the sides of the trench may tend to support the fill, allowing it to “bridge” across theexcavation, preventing the fill from consolidating under its own weight. This cancreate areas of low soil density under the pipe where seepage can occur. In addition,differential settlement and hydraulic fracture can result.The embankment dam was redesigned to include seepage controls. The structurewas rebuilt in 1990 using essentially the same embankment dam and spillwayB-60
Appendix B—Case HistoriesFigure B-50.—Loveton Farms Dam failure as viewed from upstream. Notethat the walls of the failure area are nearly vertical. The constructionrecords indicate that a large portion of the embankment dam was placedprior to installation of the CMP.Figure B-51.—Loveton Farms Dam after failure as viewed from thedownstream end of the 78-in diameter CMP spillway. Note that one of theantiseep collars, which were about 14 feet square, is visible in the breach.B-61
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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 HistoriesFigure B
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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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