Technical Manual: Conduits through Embankment Dams (FEMA 484)

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Conduits through Embankment Dams4.1.3 Conduit shape EFigure 57.—Concrete saddles are used to supportsteel pipe located within a larger access conduit.Conduit shape E (figure 50) is formed by separating two semicircular sections byshort side sections. Figure 58 shows an example of the interior of conduit shape E.Conduit shape E generally achieves maximum economy of materials by mobilizingmore of the relieving fill pressure. The sides of the conduit should be sloped to1H:10V or more through the im pervious zone to allow equipment to compact theearthfill directly against the conduit. Contractors may use straight cords to avoidusing curved forming techniques for the exterior of this shape. If straight cords areused, the designer must ensure that stress concentrations do not change andadequate concrete thickness is provided.4.1.4 Conduit shape FAn externally shaped circular conduit is more adaptable to changes in loading andstresses that may be caused by unequal fill or foundation settlement (i.e., betterdistribution of loads). As a flow surface, a circular internal cross section is usedprimarily for pressure flow conditions, since it is a very hydraulically efficient shape.The interior of a circular conduit would be similar to figure 54. The use of anexternally shaped circular conduit through an embankment dam should be carefullyevaluated due to concerns with the difficulty or inability to uniformly compact theearthfill around the conduit. Precast concrete pipe is the most often used externallyshaped circular conduit. The earthfill beneath the haunches of the conduit cannot beadequately compacted with pneumatic tired equipment and requires compaction withhand held tampers. Efforts to obtain proper compaction using hand tampers couldcause movement or displacement of smaller conduits. Improper compaction of theearthfill around the conduit and movement of the conduit can result in differential80
Chapter 4—Structural Design of ConduitsFigure 58.—An example of the interior of conduit shape E.settlement and hydraulic fracture. The use of externally shaped circular conduitsdiffers between the major dam building agencies. Reclamation does not useexternally shaped circular conduits in their designs due to concerns about theinadequate compaction of earthfill against the conduit. NRCS allows use ofexternally shaped circular conduits, if they are constructed on cradles or bedding.The use of externally shaped circular conduits (e.g., precast concrete pipe) requiresthorough inspection and strict adherence to proper construction techniques toachieve quality assurance of earthfill compaction. Figure 51 shows an externallyshaped circular conduit on a cradle. The sides of the cradle should be sloped to1H:10V or more through the im pervious zone of the embankment dam to allowequipment to compact the earthfill directly against the conduit. For guidance on theuse of cradles and bedding, see section 4.1.6.4.1.5 Conduit shape GA box (or rectangular) shape has historically been used by some agencies, such as theNRCS. Other agencies, such as Reclamation, no longer use this shape due to theobjectionable consequences. Box shapes using both reinforced cast-in-place andprecast concrete have been used in the past with varying degrees of success. Theshape shown in figure 52 illustrates a box shape with the preferred 1H:10V or moreside slopes for improved compaction of earthfill against the conduit. Historically,the box shape has used vertical sides. The designer must fully consider the81
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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
Page 67 and 68: IntroductionThe “best practices
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Page 75 and 76: Chapter 1—Generalmeans the condui
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Page 79 and 80: Chapter 2Conduit MaterialsVarious m
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Page 151 and 152: Chapter 5Foundation and Embankment
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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 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 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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