Technical Manual: Conduits through Embankment Dams (FEMA 484)

Conduits through Embankment DamsFigure 25.—PVC pipe has infrequently been used in conduit applicationswithin low hazard embankment dams. The bell and spigot joint connectionused for this type of pipe limits its use for most conduits.2.2.2 Thermoset plasticThermoset plastics are rigid after manufacturing or curing and cannot be reformed.The most commonly used thermoset plastic for lining nonpressurized conduits iscured-in-place pipe (CIPP). CIPP is also referred to as an “elastic sock.” CIPPconsists of a polyester needle-felt or glass fiber/felt reinforcement preimpregnatedwith polyester resin (USACE, 2001d, p. 11). The preimpregnation process is usuallydone at the factory for quality control purposes. On the inner surface of the CIPPliner is generally a coating or membrane of polyester, polyethylene, surlyn, orpolyurethane, depending on the type of application. The membrane provides a lowfriction and hydraulically efficient inner surface to the CIPP liner. Figure 26 showsCIPP being used to line an existing conduit. CIPP has been successfully used inrenovating deteriorated pipelines, drain pipes, and conduits through levees for over25 years. CIPP has been used for conduit renovation through embankment damssince about the mid-1990s.The advantages of using CIPP lining for conduits include:• Thermoset plastic pipe is corrosion resistant and is not affected by naturallyoccurring soil and water conditions. Thermoset plastic pipe may be preferablein certain conduit applications where aggressive water or soil chemistry wouldlimit the life of concrete or metal pipe.48