Technical Manual: Conduits through Embankment Dams (FEMA 484)

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Conduits through Embankment Damsdiameter conduits, and repeatedly perform the same tasks without sacrifice in quality.Also, the costs involved for ROV inspection are considerably less than for diveinspection. Inspection by ROV may be preferable in certain situations prior toperforming a dive inspection. This is especially important in regards to safety. AnROV that is damaged or destroyed can be replaced. However, this is notcomparable to the loss encountered by a diver who is injured or killed.Extreme caution is advised when performing an ROV inspection. The ROVoperator should be qualified, experienced, and knowledgeable about the hazardsinvolved. The potential exists for the ROV to become stuck in small diameterconduits due to offsets, sharp bends, or debris. The ROV can also becomeentangled in its umbilical cable (or the umbilical cable can become entangled withdebris, such as tree branches). ROVs can be expensive depending upon the level ofsophistication and costs involved with the retrieval of a stuck ROV can be veryexpensive and time consuming.The ROV is typically inserted into the conduit from the upstream end. Dependingon the entrance structure’s configuration, assistance may be required from a diver toassist the ROV getting past trashracks. This approach can be used where the depth,length, and/or access limits a dive inspection’s viability, but it is difficult to get theROV into the conduit. The trashracks typically have a hatch cover that can beremoved, or the ROV can also be lowered through a gate slot to access the conduit.If trashracks cannot be removed, a few of the bars may need to be cut and removedto allow insertion of the ROV. At some sites where the downstream conduit islocated within a larger conduit, an ROV can be inserted from the downstream end ofthe conduit. For downstream end insertion, the ROV is placed within the unwateredsection of conduit between the downstream guard and regulating gates/valves. TheROV cables are threaded through a special manhole in the pipe. Once the conduitsection is rewatered and the guard gate opened, the ROV can proceed upstream andinspect the conduit. This method may be difficult, especially if umbilical cable needsto be continually fed through the opening, and should only be attempted by qualifiedand experience personnel.Some of the limitations using an ROV for conduit inspection include (USACE,1995b, p. 2-15):220• Two-dimensional.—The ROV inspection provides only a two-dimensional viewand does not project the full extent of any defect. If the conduit diameter islarge, the ROV inspection is much more likely to be limited to one small pathalong the conduit, whereas a diver can cover a much larger path or wider swathas the diver moves down the conduit.• Visibility.—Murky water limits the effectiveness of an ROV inspection. Withan ROV in a limited visibility situation, the only area inspected is the small area
Chapter 9—Inspection and Assessment of Conduit-Related Problemsdirectly in front of the camera. A diver can use their sense of feel, in a limitedvisibility situation and focus in on any problem areas.• Orientation.—In some situations, it may be difficult to determine the exactorientation or position of the ROV. This can impede accurate identification ofthe area being observed. Also, since ROVs often rely upon a compass, the steelin the conduit lining and/or concrete reinforcement can affect the navigation.If a CCTV camera-crawler is used in lieu of an ROV, the length of cable tethercan be measured to determine the location within the conduit.• Maneuverability.—In some “tight” areas the ROV may have more difficulty withmaneuverability than divers would have in the same situation. Water currentscan also affect maneuverability by causing the tether to become entangled.The technology associated with ROVs is continually evolving. Continuedadvancements will allow the operator to overcome some of the existing ROVlimitations by utilizing more sophisticated attachments and instruments to improvediagnostic capabilities.9.5.4.4 Closed circuit televisionThe use of CCTV as an inspection method has undergone significant technologicaladvancements. The introduction of robotic and automated systems, such as smartpigs, camera-crawlers, and other remotely controlled vehicles has allowed previouslyinaccessible conduits to be inspected. CCTV and man-entry are the most widelyused methods of conduit inspection.CCTV is a very useful method for examining small or inaccessible conduits(figures 126, 127, and 128). CCTV inspection provides significant improvementsover other methods of inspection, such as man-entry inspection where an inspectorcrawls through the conduit (36 inches or larger) and documents the conditions,manual inspection where a sled with a camera is pushed through the conduit usinglong push rods, and mechanical inspection where a camera tethered to a wire rope ispulled through the conduit. CCTV inspection has the advantages of being able toexamine conduits regardless of size limitations, has complete mobility, and providesreal time video images.CCTV inspection also can be used in conduits where confined space entry issuesmay require permitting prior to man-entry. OSHA regulations define a confinedspace as having limited access and egress, and not being designed for continuoushuman habitation. This would include not only small conduits, but also largerdiameter conduits, where risks, costs, or system complexity may make remoteinspection more advantageous.221
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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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Page 283 and 284: Chapter 10Evaluation by Geophysical
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Chapter 11—Appropriate Emergency
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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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