Technical Manual: Conduits through Embankment Dams (FEMA 484)

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Conduits through Embankment Dams9.5.2.1 Exterior inspectionExterior inspection of the areas above and surrounding the conduit can providemany clues concerning the condition of the conduit. Items to look for include:206• Look for signs of infiltration of soil into the conduit. Depressions, sinkholes(figures 119 and 120), or cavities that exit onto the surface of the embankmentdam along the centerline conduit alignment are usually an indication thatinternal erosion or backward erosion piping is occurring. These features oftenappear as holes that line up with one another. Such features should be markedwith reference points and monitored to determine whether they are expandingwith time. Sinkholes should be probed to determine the extent of the void,which may be dome shaped and enlarge with depth. The seepage and flowconditions on the downstream slope and through the conduit, should beexamined for evidence of association with the sinkhole. Sinkholes are a causefor immediate concern and further investigation. Beware that some animalsmay take over these areas, and they may not be recognizable as sinkholes orcavities.• Look for signs of seepage or indications that seepage is sometimes present.The best time to look for seepage may be when the conduit is operating in apressurized condition or at full discharge capacity. Evaluate the following:1. If an area on the surface of the embankment dam is wet, the area shouldbe marked or staked, and photographed, to see if it is expanding overtime. If the seepage is flowing, measures should be taken, such as theinstallation of a weir, to collect and measure the quantity of flow. Aseepage rate that is increasing faster than expected, relative to the reservoirlevel, may be an indication of internal erosion or backward erosion piping.Seepage in these areas may be characterized by increased vegetativegrowth or the presence of plants that thrive in wet areas. Ifinstrumentation is available, measurements of seepage should becompared to previous measurements to reveal changes in flow rates.Piezometers should also be monitored.2. The quantity of seepage along the conduit or through the conduit’sbackfill may indicate that adequate compaction around the conduit wasnot achieved or internal erosion or backward erosion piping is occurring.The area where water outlets from a seepage diaphragm should be closelymonitored. Seepage areas may be indicated by changes in vegetation orcolor. The limits of a newly wet area should be marked to determinewhether the area is increasing in size. When possible, the seepage shouldbe channeled away from the embankment dam and directed through apipe, weir, or other device that will allow the quantity to be measured.
Chapter 9—Inspection and Assessment of Conduit-Related ProblemsFigure 119.—Sinkhole in the crest of an embankment dam.Figure 120.—Sinkhole around a spillway riser. Photo courtesy of SchnabelEngineering.Measurement of flow by a stopwatch and bucket is a simple way to collect flowinformation. Installation of a weir and staff gauge is preferred for more uniformdata collection under longer term conditions.207
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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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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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Page 231 and 232: Chapter 9Inspection and Assessment
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Chapter 10—Evaluation by Geophysi
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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 HistoriesADownstr
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Technical Manual: Conduits through Embankment Dams (FEMA 484)

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