Technical Manual: Conduits through Embankment Dams (FEMA 484)

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Conduits through Embankment Dams216• Length.—As with depth, the conduit length becomes a factor relating to theamount of time the diver has available at depth. If the conduit is extremelylong, it can take much more time to inspect than the diver has available. Theavailable dive time for a long conduit can be increased, but this can be costly.Safety also must be considered. Because the diver does not have a direct pathto the surface, the farther the diver must penetrate into the confined space, thefarther the diver is from a direct path to the surface.• Access.—Often the entrances to conduits are equipped with trashracks on theinlet side. The ability to remove enough of the trashrack bars to allow easyentry and egress is important. Since divers in such an overhead environmentwill be utilizing some type of surface-supplied breathing gas, it is important thatthe access point be such that the hoses will be able to be fed into the conduitwithout hanging up. A second diver is required to be stationed underwater atthe confined space entry point to tend the primary diver’s umbilical.• Leakage and currents.—The leakage of downstream gates or valves in a conduit isa safety factor that can affect whether a dive inspection can be safelyperformed. Currents can be unpredictable. Any inspection of this type shouldbe performed, such that the diver enters the conduit against any current andthen returns and exits with the current. In the case of an inverted siphon, thiscan be accomplished by entering from the downstream end, but in the case ofan outlet works, a submerged conduit will more than likely need to be enteredfrom the upstream end. Therefore, the condition of the gates or valves andhow much leakage is exhibited is a big factor with respect to the viability of adive inspection.• Conduit size.—A conduit should really be large enough that the diver can turnaround inside and exit head first. The size for this will obviously depend on thesize of the individual diver and also the exact type of equipment required.• Visibility.—The distance a diver can see is important to whether a diveinspection of a conduit is advisable. In poor visibility situations, the diver canuse their sense of touch for inspection. Sometimes a diver can use a hand toprobe areas that cannot be seen. In the event of zero visibility, there wouldlikely be little reason to pursue a dive inspection, as the shear magnitude of theentire surface of a conduit would be extremely difficult to inspect by touchalone. Also, in a circular conduit, a diver does not have a real edge or otherreference point to keep track of any findings. If a dive inspection (figure 123) isplanned for a conduit, consideration should be given to making a large releaseprior to the inspection as a means of flushing sediments from the conduit andthen allowing some amount of time for the water to settle out prior to diverentry. This time will depend on the type of sediments in the water, but couldvary from a day to a week. If visibility is good, the diver may want to use a high
Chapter 9—Inspection and Assessment of Conduit-Related Problemsresolution hand-held video camera to documentconditions existing within the conduit. The videocamera can be either self-contained or configured fortopside viewing. A self-contained video camera isenclosed in a special waterproof case that allows foreasy operation by the diver. For topside viewing, acable is required from the camera to the monitorlocated on the top. Audio can be provided during therecording by the diver or topside personnel. Videocameras can also be mounted on the diver’s helmet. However, no matter how good the video camera’sresolution is, if visibility is poor, the camera will onlybe able to document a few square inches of surface atone time.Sometimes in pressurized conduits, it may be difficult for adiver to determine, if a defect is allowing water to leakthrough it. In these situations the diver may want torelease colored dyes (e.g., food coloring) and observe if itgets sucked into the defect. Another option would be theuse of a wand with a string or frayed rope attached to it. IfFigure 123.—Diverperforming an underwaterinspection.water is leaking out of the conduit the string or frayed rope would be sucked into thedefect (Stoessel, Dunkle, and Faulk, 2004, p. 2). Temporary repairs by the divers arepossible by plugging these defects with Oakum or similar materials. However, amore permanent repair will need to be considered.In certain situations, the combined use of divers and ROV or CCTV equipment maybe required to complete the conduit inspection. The divers are used to gain accessto the conduit and place the ROV or CCTV equipment in the proper location tobegin the inspection.For an example of an underwater conduit inspection, see the Salmon Lake Dam casehistory in appendix B.9.5.4.2 Climb inspectionAlthough not often required for conduits, a climbing team may be utilized toperform inspection of the inaccessible portions of intake towers and the walls ofterminal structures (figure 124).9.5.4.3 Remotely operated vehicleThe ROV was first developed for industrial purposes to inspect oil and gas pipelinesand offshore platforms. ROVs are now being utilized for underwater inspections of217
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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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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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