Technical Manual: Conduits through Embankment Dams (FEMA 484)

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Conduits through Embankment Dams2083. The quality of any seepage, especially whether it is carrying soil particlesshould be analyzed. Water seeping into, out of, or along a conduit cancause problems by carrying particles with the flow. If the quality andquantity of the water flowing into the conduit is different from the waterflowing out of the conduit, then it is likely that open joints or cracks areallowing additional seepage flow to enter the conduit, or normal dischargeto leak out. The appearance of the flow at the area where water outletsfrom a seepage diaphragm is of particular concern. Any water flowing inthe vicinity of the conduit should be observed for evidence of fines beingtransported, such as cloudiness or discoloration. The internal erosion andbackward erosion piping processes can occur intermittently, with finesbeing transported sporadically. Evidence of fines being carried in seepageis cause for concern, further investigation, and prompt action.The monitoring of any condition involving seepage or discharge should alsoinclude the corresponding reservoir pool level. Any sudden change, or unusualtrend over time, which does not correspond to changes in the reservoir level,could indicate a seepage problem. For example, an increase in the seepage ratewhile the pool level is constant could be an indication of internal erosion. Poollevels may be measured by a staff gauge, by calibrations placed on a fixedstructure in the reservoir, or by water-level sensing devices.• Look for signs of internal erosion or backward erosion piping where theconduit exits the downstream slope of the embankment dam near the terminalstructure. Water flowing through cracks in the earthfill or along the conduitmay erode soils and cause a cloudy effluent with turbulent flow. Deposits ofsand may form at the exit point of seepage. Water escaping from intergranularseepage in granular soils may create sand boils, and the flow is less likely to beturbid. Other indicators of developing problems include deposits of sedimentnot associated with runoff, sinkholes, and signs of settlement, such asdepressions on the surface of the embankment dam or its foundation.• Any changes in the embankment dam or foundation in the vicinity of theconduit. Since the location of a conduit represents a unique condition in theembankment dam, and a potential seepage path through the dam, any changesin the vicinity of the conduit should be investigated. Such changes mightinclude slope movement, changes in vegetation, areas of new or unexpectedwetness or seepage, unusual piezometric readings, etc.• Check the exposed areas of the conduit for cracking, weathering, and/orchemical deterioration.• Look for any whirlpools in the reservoir in the vicinity of the conduit.
Chapter 9—Inspection and Assessment of Conduit-Related Problems• During operation of the conduit, additional items of concern include:1. Any unusual noises, such as popping, banging, or vibrations should beinvestigated. Vibrations may occur, if the conduit is not properlysupported. Vibrations could adversely affect the conduit and surroundingbackfill.2. Color changes or fines observed in the discharge water coming out of theconduit.3. Pulsating or unstable flow.4. Unexplained reductions in discharge capacity.9.5.2.2 Interior inspection.Typical problems within the interior of conduits include deterioration, obstructions,joint offsets and separations, defective joints, cracking, and mechanical equipmentmisoperation (figures 121 and 122).If the conduit is accessible, the inspector should use a measuring tape or pace off thelocations of all damaged or questionable areas within the conduit. Damage orquestionable areas should be documented using still, digital, or video cameraequipment. If the conduit is inaccessible, CCTV inspection equipment should beutilized.The interior inspection should look for:• Water ponding on the invert of the conduit, which could be an indication ofsettlement-related problems in certain reaches of the conduit, especially if theconduit as-built drawings show a constant invert slope.• The locations of cracks should be documented using a crack map or similarreporting method. Be aware of any previously reported cracks, and note anynew cracks. The length and width of the crack should be measured. To get anindication of the continuity of cracks through a concrete structure, use ageologist’s pick or similar hammer to tap the concrete and listen for changes ofpitch that give clues to the condition of the concrete. At some selected siteswhere accessible conduits are constructed on compressible or nonuniformfoundations, strain gauges, total stress cells, and crack meters have been used tomonitor changing conditions. For guidance on performing a crack survey, seeUSACE’s Evaluation and Repair of Concrete Structures (1995b, pp. 2-1 to 2-13). For209
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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
Page 195 and 196: Chapter 7Potential Failure Modes As
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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 Historiesdownstre
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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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