Technical Manual: Conduits through Embankment Dams (FEMA 484)

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Conduits through Embankment DamsFigure 94.—Filter collar surrounding a conduit renovation.New downstream embankment materialGravelenvelopeFilter collar (sand)ExistingconduitPerforated collector pipeNew concrete conduitencasement (reinforcementnot shown)Section A-AFigure 95.—Cross section showing a filter collar surrounding aconduit renovation. The drain pipes located on both sides of theconduit collect and convey any seepage within the filter collar to adownstream exit location.146
Chapter 6—Filter Zonesfiltering the sand and providing a controlled outlet for the collected seepage. Thegravel should meet filter criteria for the sand filter.At the very downstream toe of the embankment dam, a short section of perforateddrain pipe (similar to a toe drain) is often provided to collect and convey any seepagewater out of the filter collar. This collector pipe will help keep the toe area frombecoming boggy. The pipe will also provide opportunity to measure seepage flowand monitor for sediment transport. Provisions should be made in the design of thecollector pipe to allow for inspection by CCTV equipment. See section 9.5.4.4 for adiscussion of CCTV inspection.Burying the collector pipe too far into the embankment should be avoided. Thegravel envelope drain should be capable of providing the needed drainage. Thedesigner should provide access provisions for the collector pipe to enable inspectionand cleaning. Also, should the collector pipe become damaged, it should be locatedsuch that it can be removed and replaced.6.6 Filter and drain gradation designDesigning the gradation of the sands used in the filter is important if they are tofunction properly. Standard filter design methods, such as the NRCS designprocedure shown in Gradation Design of Sand and Gravel Filters, National EngineeringHandbook, Part 633, Chapter 26 (1994), the USACE’s General Design and ConstructionConsiderations for Earth and Rock-Fll Dams (2004a), and Reclamation’s EmbankmentDams—Protective Filters (1999) are typical. Materials suitable for filters will rarely beavailable onsite and are usually purchased from concrete aggregate suppliers orprocessed from materials near the site. For many designs, ASTM C 33 fine concreteaggregate is found to meet criteria. However, designers should always determine arange of compatible filter gradations that will protect the soils used in thesurrounding embankment to increase construction flexibility. Sands used toconstruct filter diaphragms, filter collars, or chimney filters should be filtercompatible with the embankment zones being protected, and they must also be ableto deform and fill any cracks that may be propagated to the filter. If the filter doesnot have a property referred to as “self-healing,” the crack could propagate throughthe filter, and the filter would not satisfy its intended function. Vaughan and Soares(1982, p. 29) and the USACE (1993, p. 8-6) have described a simple test forevaluating the self-healing ability of a filter. Factors that influence the ability of afilter to be self-healing are the percentage of fines (percent finer than the No. 200sieve) and the plasticity of the fines. Filter designs usually require a low percentageof nonplastic fines (usually less than 5 percent as measured after placement in theembankment dam and compaction of the filter) to ensure that filters have adequatepermeability and self-healing characteristics. Fine, poorly graded filters have less147
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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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Page 151 and 152: Chapter 5Foundation and Embankment
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Page 169 and 170: Chapter 6Filter ZonesZones of desig
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Page 195 and 196: Chapter 7Potential Failure Modes As
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Page 215 and 216: Chapter 8Potential Defects Associat
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Page 231 and 232: 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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