Technical Manual: Conduits through Embankment Dams (FEMA 484)

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Conduits through Embankment Dams• Replacing the embankment dam slope protection.Figure 58 shows Pablo Dam as it was nearing completion.Lessons learnedSometimes repairs alone are not fully robust enough to address all the unknownerosional mechanisms existing within an embankment dam. Due to continued damsafety concerns, more extensive measures may be warranted.ReferenceBureau of Reclamation, Technical Construction Report-Pablo Dam Modification Contract No.CSKT/SOD 06, August 1996.B-76
Appendix B—Case HistoriesProject name: Pasture Canyon DamLocation: ArizonaSummary: Closed circuit television inspection of an outlet works conduitPasture Canyon Dam is located on the Hopi Indian Reservation in Arizona. PastureCanyon Dam is a homogenous embankment dam with a height of 17 feet. Theembankment dam crest is at elevation 4890.0 feet, 20 feet wide, and 632 feet inlength. The embankment dam was apparently founded on pervious, sandy alluvium.No information was available as to its construction. The embankment dam wascompleted in 1920s or 1930s and modified in 1975. The 1975 modification includeda 3-foot crest raise.Appurtenant structures at the site include an uncontrolled earthen spillway and anoutlet works. The outlet works is located within the embankment damapproximately 200 feet from the left abutment. The outlet works consists of aconcrete intake structure, approximately 55 feet of 12-inch by 12-inch masonryconduit connected to 35 feet of 14-inch diameter CMP connected to 20 feet of14-inch diameter concrete pipe. The intake structure contains a hand-operated slidegate. The discharge capacity of the outlet works has been estimated to be 9 ft 3 /s.The Bureau of Reclamation’s Technical Service Center performed a CCTVinspection of the outlet works conduit at Pasture Canyon Dam in April 2004. Theconduit was accessed for inspection, via an existing manhole located at thedownstream end of the outlet works. The camera-crawler was inserted into the14-inch diameter concrete pipe and was advanced upstream approximately 18 feet,where the concrete pipe ended and CMP began. Water clarity was somewhat poorand limited viewing throughout the conduit. The camera-crawler was advancedupstream within the CMP for approximately 35 feet, where the CMP ended and amasonry conduit began. The camera-crawler was advanced upstream within themasonry conduit for approximately 30 more feet, where numerous piles of sand wereobserved near the sidewalls of the masonry conduit. Figure B-59 shows a typical pileof sand near the sidewall of the conduit. In addition, just a few feet into the masonryconduit existed an open defect (crack) in the crown of the conduit. Figure B-60shows the defect at the crown of the conduit. This defect allowed sand materials toenter the conduit. Based on observations made during the CCTV inspection, it wasconcluded that Pasture Canyon Dam was in the process of failing by internal erosionor backward erosion piping, and immediate action was required. Visual monitoringof the embankment dam and monitoring of the area around the outlet works wasperformed every 4 hours. The Bureau of Indian Affairs (BIA) imposed reservoir andgate operating restrictions at Pasture Canyon Dam.B-77
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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 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 Historiesproject,
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Appendix B—Case Historieswatersto
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Appendix B—Case HistoriesLessons
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Technical Manual: Conduits through Embankment Dams (FEMA 484)

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