Technical Manual: Conduits through Embankment Dams (FEMA 484)

Chapter 4—Structural Design of Conduitsplacement. The most secure way to support waterstop during concreteplacement is with the use of properly built forms (commonly referred to as splitforms). Figure 78 shows an example of a waterstop inserted through a speciallycut slot in the form. Additional support is provided to the waterstop on thenonplacement side, to ensure no movement occurs. Proper waterstopinstallation requires that one-half of the waterstop be embedded on each side ofthe joint. Nailing, stapling, or insertion of wire through the waterstop shouldnot be allowed, since this may affect the integrity of the material and shortenthe seepage path around the waterstop. Often contractors use hog ringfasteners crimped along the edge of the waterstop and wired to reinforcing steelto secure the waterstop. If hog rings are used, extreme care should be exercisednot to pierce the waterstop when crimping, since this could result in shorteningof the seepage path around the waterstop. Also, reinforcing bars should not beallowed to penetrate the waterstop.• Poorly spliced waterstop.—Since the PVC waterstop is thermoplastic, it can bespliced at the construction site as needed. The ends of waterstop to be splicedshould be properly aligned, true, and straight. A miter-box guide and portablesaw is typically used to cut waterstop. The proper splicing of waterstoprequires the use of an electric thermostatically controlled waterstop splicingiron. Sometimes contractors will use a welding torch in an attempt to splice thewaterstop together (Zomok, 2004, p. 3). A torch will cause PVC to burn,resulting in a poorly spliced waterstop joint. The joints should not be lapped.Approved manufacturer recommendations should be followed for splicing.• Poorly consolidated concrete.—During concrete placement, the concrete surroundingthe waterstop should be adequately vibrated, such that the waterstop iscompletely embedded in concrete. Inspectors should pay close attention duringconstruction for proper waterstop installation. Any improperly installed orspliced waterstop should be removed and replaced. The contractor’s proposedmethod of waterstop installation should be carefully reviewed prior tobeginning any work. Approved manufacturers’ installation recommendationsshould be carefully followed.The use of waterstops across control joints is advised even for steel lined conduits.Guidance on the design of waterstops is available in the USACE’s Waterstops andOther Preformed Joint Materials for Civil Works Structures (1995e). The Arkabutla casehistory in appendix B illustrates the importance of using waterstops in theconstruction of conduits.4.3.2.2 Precast concreteFor all precast concrete pipe, a rubber gasket (figures 66-69) provides the primarybarrier against movement of water or soil into or out of the conduit. The spigot end109