Technical Manual: Conduits through Embankment Dams (FEMA 484)

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Conduits through Embankment Damslengths (frequencies) propagate at different velocities through nonhomogeneousmaterials. This variation in velocity is related to the shear wave velocity and thusshear modulus (Shaw, 2003).Different equipment is used depending on whether the SASW/MASW technique isto be used for geotechnical analysis of soil (to depths of 3 feet to 300 feet), or forstructural evaluation of concrete. The equipment generally consists of two or moregeophones, a hammer or other impact device for generating vibrations, and aseismograph or other data collection unit.Higher wave frequencies and close geophone spacing are used for shallowinvestigations, and lower frequencies with wider spacing are used for deeperinvestigations. The field data are later processed with specialized software, such asWinSASW, developed by the Geotechnical Engineering Center of the University ofTexas at Austin, or SurfSeis, developed by the Kansas Geological Survey.10.2 Self potentialSelf potential (sometimes referred to as streaming potential or SP) (figure 141),measures the electrical potentials (or voltages) that exist in the ground or within anembankment dam. Flowing water naturally generates these potentials as aconsequence of the separation of ions in the seepage water itself. SP is considered tobe the only geophysical method capable of direct detection of seepage (Corwin,2002). Other geophysical methods, such as resistivity, infer the existence of seepagebased on other measured parameters.Theoretically, it is possible to measure these potentials and predict seepageanomalies, such as along a conduit within the embankment dam, up to severalhundred feet deep. However, the technique is not widely applied, and few people orcontractors can expertly interpret the data. In addition, the measured potential(usually on the order of tens of millivolts) in any area can vary with other in-situparameters, and with man-induced voltages.Existing procedures were developed for the USACE’s Waterways ExperimentStation and published in 1989 (USACE, 1989), and also for the Canadian ElectricityAssociation Dam Safety Interest Group (Corwin, 2002). SP interpretation andmodeling computer programs are beginning to be developed along the lines ofexisting programs available in other geophysical disciplines, such as resistivity andseismic methods.Canadian Electricity Association Technology, Inc. has published a series of DOSprogram codes (Corwin, 2002) and the University of British Columbia has availablea modeling procedure that runs under Visual ModFlow, and models the SP response250
Chapter 10—Evaluation by Geophysical and Nondestructive TestingFigure 141.—Collecting self potential (SP) data on the crest of anembankment dam in Virginia to trace the source of observed seepage. The75-ft high embankment dam had a sinkhole, a sand boil, and severalseepage points on the downstream face. This information was used incomplement with electrical resistivity imaging data. Photo courtesySchnabel Engineering.for a user input distribution of permeability and electrical resistivity parameters(Sheffer, 2002).Self potential measurements are affected by soil moisture, resistivity, temperature,and other in situ parameters. Therefore, the SP technique should be combined withother methods, such as resistivity or temperature measurement.10.3 Electrical resistivityElectrical resistivity technology is relatively well developed and can be a veryeffective tool for locating large buried metal targets, and other highly electricallyresistive or highly conductive targets (Ward, 1990) . The technique, involving anarray of electrodes that measure the distribution of voltage applied to the ground,has been used to investigate some embankment dams. However, small changes inmeasured data can result in very different interpretations. Resistivity interpretationsare nonunique, and should be constrained by independent data. Other fieldparameters (permeability, dissolved minerals, temperature) may need to be measuredat the same time. The method is sensitive to interference from nearby metal objects(such as pipes and wires within the embankment dam, or overhead wires and fences).251
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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 9—Inspection and Assessme
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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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