Technical Manual: Conduits through Embankment Dams (FEMA 484)

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Conduits through Embankment DamsFigure 115 shows an example of poor construction practice (improper consolidationof concrete). For an example of how poor design and construction practice can leadto the failure of a concrete conduit, see the Olufson Dam case history in appendix B.Poor design and construction practices particular to reinforced cast-in-place conduitswere discussed in the previous paragraphs. However, poor design and constructionpractices affect all types of conduits. The following paragraphs briefly discuss effectsof poor design and construction practices affecting other types of conduits, such asprecast concrete, or CMP. The appearance of these defects can lead to preferentialseepage paths and the development of potential failure modes for conduits. Some ofthese include:• Deformation.—Deformation occurs when load or force changes the shape of theconduit. Deformation is typically caused by the application of excessiveexternal load (e.g., improper selection of design loadings), loads from heavyconstruction equipment, or seismic activity. Figure 116 shows an example ofwhere heavy construction equipment likely caused deformation of a CMPconduit. CMP is flexible and is designed to deform some as it transfers loadinto the surrounding backfill. The surrounding backfill provides stiffness andload carrying capacity. Improperly designed backfill or inadequately compactedbackfill under the CMP haunches does not provide the needed lateral stiffnessto the CMP. This can result in excessive deformations and structural failure orcollapse of the CMP (Kula, Zamensky, and King, 2000, p. 3).• Differential settlement.—Differential settlement occurs when the embankmentmaterials next to the conduit are improperly or inadequately compacted orwhen the conduit is placed on a foundation of varying density. The conduitlocation and the resultant embankment loading can result in differential190Figure 115.—A rock pocket at the bottomof a conduit side wall.
Chapter 8—Potential Defects Associated with ConduitsFigure 116.—Deformed CMP conduit. Deformation likely occurred duringoriginal construction, possibly from construction equipment traveling overthe conduit with inadequate earthfill cover.settlement problems. Differential settlement affects the structural integrity ofthe conduit by causing distress to the conduit in the form of misalignment(vertical or horizontal), shape distortion, joint offsets/separations, cracks, orspalls. Differential settlement occurs when one section of conduit settles morethan the rest. This typically occurs at joints in the conduit (figure 117). Thesettling process can open these joints and provide a path for water either into orout of the conduit. Examples of differential settlement and the resultingdamage are:1. Spreading of the embankment dam, causing separations in the conduitjoints. As compressible soils under the embankment dam consolidate,some spreading is inevitable. As soils spread laterally, sections of theconduit may separate, leaving joint openings through which water canthen move.2. Differential settlement due to foundation discontinuity, causing offsettingof joints.3. Differential settlement of the embankment dam, causing loads greaterthan the conduit can accommodate, resulting in cracking and excessivedeformation of the conduit.• Misalignment.—Misalignment occurs when poor construction practice allows foralignment deviation or from improper or inadequate compaction of191
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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 ZonesFigure 89.
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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 9—Inspection and Assessme
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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 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 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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