Technical Manual: Conduits through Embankment Dams (FEMA 484)

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Conduits through Embankment Damsstem is retrieved. The most common pipe material is HDPE, although PVC andsteel can be used.Legitimate concerns are associated with the fluid pressures used for excavationduring the horizontal directional drilling process, and the potential for hydraulicfracturing of the embankment dam. Reasonable limits must be placed on maximumfluid pressures in the annular space of the bore to prevent inadvertent drilling fluid“returns” to the ground surface. However, it is equally important that drillingpressures remain sufficiently high to maintain borehole stability, since the ease withwhich the pipe will be inserted into the borehole depends upon borehole stability.The drilling pressures should be measured in the borehole, not at the pump. Thein-situ pressures should be compared with theoretical criteria that would causehydraulic fracturing of the adjacent soils. In a test study by the U.S. Army Corps ofEngineers, it was found that the pressure in an HDD hole drilled through a leveeembankment was nearly independent of the drill rig pump pressure. Monitoring ofpiezometers in the embankment levee showed that while significant increases in porepressures in the embankment occurred as drilling operations progressed, thepressures quickly dissipated to their original levels. Studies on plastic behaviorshowed that fluid pressure may cause hydrofracture (figure 190) when the pressureexceeds twice the value of undrained cohesion of the soil, that is, the unconfinedcompressive strength of the soil. Therefore, a pressure of 100 lb/in 2 would beexpected to cause hydrofracture in a clay with an unconfined compressive strengthless than 7.2 t/ft 2 , a very stiff clay. According to these assumptions, for a compactedsaturated clay with a soil unit weight of approximately 125 lb/ft 3 , 8.7 lb/ft 2 for each10 feet of depth would be required to cause hydrofracture. However, these studiesdid not address the propagation of hydrofracture through the soil but focused solelyon the pressures required to initiate hydrofracture. Studies on the elastic behaviorcompared the stresses on the boundary of the hole and compared these stresses withthe tensile strength of the soil. The coefficient of lateral earth pressure was varied todetermine its effect on hydrofracture potential. As the ratio of horizontal soil stressto vertical soil stress approached unity, the stresses required to producehydrofracture were comparable to those computed for the plastic deformationanalysis. The fact that hydraulic fracture has not been observed in many HDDprojects where the theoretical criteria have been exceeded makes it clear thatimportant factors have been ignored (USACE, 1998b, p. 6).A properly designed filter diaphragm or collar should be constructed near thedownstream end of the pipe to intercept and control potential seepage along theoutside of the conduit. For guidance on the design and construction of the filter, seechapter 6.342
Chapter 13—Replacement of ConduitsFigure 190.—Hydraulic fracture of embankment leveeduring HDD installation is visible in this photograph. Thedrilling mud, which was dyed pink, so that suchfractures could be observed, followed an interface alonga clay seam (USACE, 1998b, p. 29).343
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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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Page 383 and 384: Chapter 14Repair and Abandonment of
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Page 401 and 402: ReferencesThe following references
Page 403 and 404: ReferencesBureau of Reclamation, De
Page 405 and 406: ReferencesCooper, Chuck, E. Wesley
Page 407 and 408: ReferencesJacobsen, S., “Buckling
Page 409 and 410: ReferencesNatural Resources Conserv
Page 411 and 412: ReferencesU.S. Army Corps of Engine
Page 413 and 414: ReferencesWooten, R. Lee, Peter S.
Page 415 and 416: Additional ReadingThe following ref
Page 417 and 418: Additional ReadingCarter, Brent H.,
Page 419 and 420: Additional ReadingJohnson, Brian, J
Page 421 and 422: Additional ReadingNatural Resources
Page 423 and 424: Additional ReadingU.S. Army Corps o
Page 425 and 426: Additional ReadingVan Aller, Hal, R
Page 427 and 428: GlossaryThe terms defined in this g
Page 429 and 430: 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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