Technical Manual: Conduits through Embankment Dams (FEMA 484)

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Conduits through Embankment DamsFigure 105.—Abrasion/erosion damage to concretefrom flowing water containing sand and silt.This flow causes a scouring or grinding effect on the exposed surface. Mostconduits do not carry significant amounts of abrasive materials in the flow.However, conduits used for diversion during construction or for reservoir sedimentrelease are especially vulnerable. Increases in the velocity of the flow can increasethe abrasive power.In concrete conduits, abrasive damage has been experienced in concrete with lowstrength and poor quality aggregates. Abrasive flow usually erodes the cementmortar mix matrix, leaving an exposed, polished, and coarse aggregate surface. Asthe abrasion process continues, the concrete may be eroded down to thereinforcement. The extent of damage depends on the flow duration and velocity,concrete quality, and compressive strength. In concrete conduits, abrasion isgenerally not a factor when velocities are less than 15 ft/s. In metal conduits,abrasive flow can erode protective linings and coatings and expose the surface tocorrosion.Once damage from abrasion has begun, it will accelerate with each operation of theconduit, unless the source of the abrasive materials is removed. Cavitation may alsobe triggered by the abrasion damage (by creating a flow surface irregularity) andgreatly increase the rate of destruction.Polyethylene plastic pipe has been found to be very abrasion resistant. However,high velocity flow containing abrasive materials can still be problematic for any typeof pipe.8.1.2 AgingThe aging process can also cause deterioration in conduits. In concrete, propertieschange over time and eventually affect the integrity of the structure (Pinto, 1994, p.1111). Both the quality of concrete (e.g., porosity), and physical and chemical factorsinfluence the rate of concrete deterioration. Processes that can weaken concreteinclude:178
Chapter 8—Potential Defects Associated with Conduits• Freezing and thawing.—Repeated cycles of freezing and thawing can affect thedurability of concrete. Concrete readily absorbs water and is vulnerable todamage, if the water within its system of pores can freeze and generatedisruptive pressures. If the pores existing in the concrete are inadequate in sizeand number to accommodate the greater volume occupied by the ice, theconcrete will fracture. The rate of progression of the freezing and thawingdeterioration will depend upon the number of cycles, the degree of saturationduring freezing, the porosity of the concrete, and the exposure conditions.Concrete experiencing damage by freezing and thawing is characterized by adisintegrated appearance. Deterioration due to freezing and thawing isespecially severe in the northern and mountain zones of the United States.Deterioration from freezing and thawing progresses from the exterior surfaceto the concrete inward. As the concrete on the surface fails and is removed byspalling, the depth of freezing progresses inward (Reclamation, 2003, p. 7).Freezing and thawing typically is not a significant concern for conduits, sincemost of the conduit is submerged or has limited exposure. However, freezingand thawing can become a problem for entrance and terminal structures.Figure 106 shows a concrete intake structure that has been exposed to repeatedcycles of freezing and thawing. In new construction, the entrainment of smallbubbles of air into fresh concrete has been found to provide relief for pressuresdeveloped by free water as it freezes and expands. Repairs to existing structuresrequire replacement concrete or epoxy-bonded concrete (Reclamation, 1997,p. 26).Figure 106.—Concrete deterioration from freezing and thawing.179
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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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Page 231 and 232: 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 Historiespipe. Du
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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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