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Technical Manual: Conduits through Embankment Dams (FEMA 484)

Technical Manual: Conduits through Embankment Dams (FEMA 484)

Technical Manual: Conduits through Embankment Dams (FEMA 484)

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Chapter 4—Structural Design of <strong>Conduits</strong>Figure 79.—A rubber gasket is installed atthe spigot end of the precast concrete pipe.Quality installation is critical to ensure precast pipe joints are assembled watertightand will remain watertight after the pipe settles and moves. Several careful steps arerequired (NRCS, 2001b):• Pipe section shall be set to specified line and grade and temporarily supportedon precast blocks or wedges until the sections are joined and the cradle is cast.For guidance on use of cradles, see section 4.1.6.• The connecting surface of the bell and spigot shall be thoroughly cleaned anddried.• The gasket and the bell surface shall be coated with a light coat of softvegetable soap compound.• The spigot shall be seated to within 0.5 inches of its final position and theposition of the gasket checked with a feeler gauge around the entirecircumference of the pipe. Detection of any improperly seated gasket willrequire disassembly.• A sealing compound (mastic) shall be applied to completely fill the exteriorannular space between the placed pipe sections. Figure 80 shows mastic beingapplied to the annular space of a precast pipe.• The sealing compound shall be covered with a metal or geotextile band wherestones larger than ¼ inch may occur in the backfill material.111

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