Technical Manual: Conduits through Embankment Dams (FEMA 484)

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Conduits through Embankment Damsdifficult to obtain good compaction of the fill soils under and alongthe CMP and around the antiseep collars .........................B-10B-11 Seepage along the sides of the CMP resulted in loss of soil support, causing conduit and joint deformation ...........................B-10B-12 Arial view of Arkabutla Dam, Mississippi.........................B-12B-13 Cross section of the outlet works conduit.........................B-14B-14 Metal plate bolted across the joint...............................B-15B-15 Damaged metal plate .........................................B-16B-16 Cracking at the embankment dam crest above the sinkhole on the upstream slope of the embankment dam. Note the simple staking ofthe area to monitor movement of the crack .......................B-19B-17 Portable pump used to initiate draining of the reservoir ............. B-20B-18 Initialization of the breach in the embankment dam near the left abutment ................................................... B-21B-19 Discharge of water through partially breached section and down thedownstream slope of the embankment dam ....................... B-21B-20 Large spall at the construction joint located at station 12+13 ......... B-23B-21 Exposed aggregate located at station 11+28.......................B-23B-22 Popout located at station 10+79 . . . . . . . . . . . . . . . .................B-24B-23 Spall at the construction joint located at station 4+93 ............... B-24B-24 Because of soft foundation soils, numerous 60-foot long pipe piles were installed in winter 2001 to support a new reinforced cast-in-placeconcrete spillway structure . . . . . . . . . . . . . . . . . . . . ................. B-27B-25 This the downstream end of the spillway at the end of construction in 2002....................................................... B-27B-26 Less than 2 years later, an engineer inspecting the bridge over the spillway reported that seepage flow was visible from under thedownstream end of the spillway. The seepage flow was clear, and nomigration of soils was evident. A few months later, the roadway onthe dam crest collapsed, and large quantities of sediment wereobserved in the pool below the dam . . . . . . . . . . . . .................B-28B-27 The road was closed immediately, and lake level was lowered. However, the sinkhole rapidly enlarged ..........................B-28B-28 Seepage flow at the downstream end of the spillway appeared to be boiling. Attempts to create a sandbag weir around the boil to reduceleakage under the spillway were unsuccessful . . . . . .................B-29B-29 A sinkhole, which appeared in a heavily traveled roadway above a 20-year old CMP spillway, was filled with asphalt. Part of the roadwaywas closed when the asphalt patch subsided a few hours later ........ B-30B-30 Ground penetrating radar investigations were performed from theembankment dam crest .......................................B-32B-31 Ground penetrating radar identified the location of voids along the CMP ......................................................B-32B-32 The failed CMP and voids were filled with a stiff compaction grout . . . B-33xxvi
ContentsB-33 Aerial view of Como Dam, Montana ............................B-34B-34 Installing the steel pipe slipliner within the existing outlet worksconduit ....................................................B-35B-35 A well designed siphon was to be installed through the dam crest ..... B-37B-36 A man-entry inspection of this 60-inch CMP noted seepage and extensive loss of embankment soil at two locations ................. B-39B-37 Erosion scarp on downstream slope of the embankment dam at the location of the overtopping of the dam crest . . . . . .................B-42B-38 Excavation of the controlled breach in the embankment dam ........ B-43B-39 Completion of the initialization of the breach in the embankment dam .......................................................B-43B-40 Deepening of the initial breach channel ..........................B-44B-41 Idealized cross section of Hernandez Dam .......................B-46B-42 Settlement of the outlet conduit at Hernandez Dam ................ B-48B-43 Lake Darling Dam outlet works discharge, circa 1990 .............. B-50B-44 A cross section with a profile of the outlet works and design cross section of Lake Darling Dam................................... B-51B-45 Grouting operations within the conduit ..........................B-53B-46 Aerial view of the breached Lawn Lake Dam and downstream floodplain ..................................................B-55B-47 Right side of the breached Lawn Lake Dam.......................B-55B-48 Left side of the breached Lawn Lake Dam........................B-55B-49 The pipe joints separated when foundation movement occurred duringconstruction of the embankment dam. ..........................B-58B-50 Loveton Farms Dam failure as viewed from upstream. Note that the walls of the failure area are nearly vertical. The construction recordsindicate that a large portion of the embankment dam was placed priorto installation of the CMP .....................................B-61B-51 Loveton Farms Dam after failure as viewed from the downstream end of the 78-in diameter CMP spillway. Note that one of the antiseepcollars, which were about 14 feet square, is visible in the breach ...... B-61B-52 The failed embankment dam was repaired with a new 78-in diameter CMP spillway. However, soon after reconstruction, this failed joint wasdiscovered at the upstream end of the pipe near the riser. A large voidwas also observed in the adjacent embankment fill. Note the o-ringgasket has been displaced from the joint.......................... B-62B-53 Existing 6-foot diameter elliptical conduit . . . . . . . .................B-64B-54 The embankment dam was constructed with antiseep collars ......... B-67B-55 When the pool level of this embankment dam was only about 2 to 3 feetdeep, flow along the outside of the CMP resulted in loss of the adjacentsoils .......................................................B-68B-56 Sinkhole in the dam crest the night of December 11, 1996 . .......... B-70B-57 View of upstream dam crest nearing completion of breach ........... B-71B-58 Pablo Dam nearing completion.................................B-75xxvii
Page 1: Technical Manual:Conduits throughEm
Page 5 and 6: PrefaceTens of thousands of conduit
Page 7 and 8: Prefacecondition. The hazard classi
Page 9: PrefaceLakeLine MagazineMaryland Da
Page 16: Conduits through Embankment Dams11.
Page 19 and 20: Contents23 Precast concrete pipe be
Page 21 and 22: Contents81 On first filling, a high
Page 23 and 24: Contents117 This conduit was severe
Page 25 and 26: Contents158 An example of a histori
Page 27: ContentsFigures in the AppendicesNo
Page 31 and 32: ContentsB-81 Cross section of Wiste
Page 33 and 34: ContentsMASW, multichannel analysis
Page 35 and 36: Symbolsc, cohesionE', modulus of so
Page 37 and 38: ContentsD 3350D 4221D 4253D 4254D 4
Page 39 and 40: IntroductionConduits convey water f
Page 41 and 42: IntroductionFigure 3.—A 15-inch d
Page 43 and 44: Introductionunstable. When seepage
Page 45 and 46: IntroductionAn embankment dam with
Page 47 and 48: A vortex may form at the location w
Page 49 and 50: IntroductionWater from the reservoi
Page 51 and 52: IntroductionFlowing water from the
Page 53 and 54: IntroductionThe process of dislodgi
Page 55 and 56: Introductionbe observable at the su
Page 57 and 58: IntroductionFigure 11.—Example of
Page 59 and 60: Introductionwhere conduits were ass
Page 61 and 62: Introduction• Conduits within lev
Page 63 and 64: IntroductionFigure 12.—An example
Page 65 and 66: Introductionmore recent practiced h
Page 67 and 68: IntroductionThe “best practices
Page 69 and 70: Chapter 1GeneralConduits have been
Page 71 and 72: Chapter 1—GeneralFigure 14.—Ant
Page 73 and 74: Chapter 1—GeneralFigure 17.—Fai
Page 75 and 76: Chapter 1—Generalmeans the condui
Page 77 and 78: 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 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 Historiesdownstre
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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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