Technical Manual: Conduits through Embankment Dams (FEMA 484)

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Conduits through Embankment DamsOne- or two-dimensional, or tomographic software can be used to process the data,which can be displayed as color plots of resistivity versus depth. Currently, availablefield equipment is capable of obtaining and automatically processing large numbersof resistivity measurements, regardless of data quality. Automatic processing canlead to misinterpretation of the data, if the operator does not recognize the problem,or is not familiar with nonuniqueness effects in conducting resistivity surveys.10.4 Ground-penetrating radarGround-penetrating radar (GPR) uses high frequency electromagnetic energy topenetrate below the ground surface (figure 142). An antenna is used to transmit ashort duration pulse, which travels through the air and the subsurface until it isreflected back by a change in the dielectrical properties of the material being imaged.The resulting reflections are displayed in sounding or section format, with sectionsbeing the far more common display mode. If the GPR profiles are conducted on aclose spacing, the resulting data can be treated in a data volume manner, allowingarbitrary slices through a three-dimensional data mass. This three-dimensionaltechnique can be labor intensive to acquire and process.GPR can be used to locate possible void, stope, or incipient sinkhole areas.However, the depth of penetration of radar waves in soils and concrete dependsstrongly upon the electrical resistivity of the material in question. Saline pore waterand clay-rich soils can severely limit this depth of penetration. Metals are opaque toradar energy, so complete radar wave reflection occurs at metal surfaces, such assteel conduit and rebar. Soils or concrete behind such metallic objects will haveshadow zones or other absence of data.252Figure 142.—Conducting a ground-penetrating radar survey across damcrest to locate voids beneath roadway and spillway. Photo courtesySchnabel Engineering.
Chapter 10—Evaluation by Geophysical and Nondestructive TestingKnown void areas are extremely useful in “calibrating” a GPR survey at a particularsite. Lacking known void areas, core drilling or other direct inspection methods arehighly desirable to aid in the GPR data interpretation. GPR data profiles can bedifficult to interpret properly, if no site “ground truth” is available. Figure 143shows a core hole being drilled to reveal voids behind the concrete, and figure 144shows an example of GPR profiles along a conduit invert.Because the radar waves travel equally well in all directions, GPR may be used toimage from the inside of a (nonmetallic) conduit outwards, along crown, springlines,and invert. Modern GPR equipment is commonly mounted on a cart or pole toallow imaging in the required direction. Note that steel well casings, communicationcables, metal buildings, overhead wires, and other cultural features can causeanomalous-looking radar profiles. The GPR interpreter must be aware of thelocations of such features at the site.10.5 SonarFor inundated conduits with a heavy suspended sediment load and very poorvisibility, three-dimensional real-time imaging sonar is advantageous. A rotatingsonar transducer mounted on a sled, crawler vehicle, or ROV can be used to scanand record the condition of a conduit (Sonex Corporation, 2002). Since the timesFigure 143.—A core hole is being drilled to reveal voids behind theconcrete in this conduit.253
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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
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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 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 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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