Technical Manual: Conduits through Embankment Dams (FEMA 484)

Chapter 2—Conduit MaterialsFigure 30.—Cast iron pipe is notconsidered acceptable for use inconduit applications.(galvanized), aluminum, or aluminized zinc alloy. Additional coatings, such asbituminous, have been applied for added protection against corrosion and abrasion.CMP was first used for conduits in the late 1890s. Generally, round pipe rangesfrom 6 inches to 26 feet in diameter. Other shapes and sizes of CMP are available,but have had limited applications in conduits through embankment dams. CMP istypically joined with coupling bands that extend over several corrugations on eachend of two adjoining pipes. The coupling bands are designed to be mechanicallytightened against the pipe corrugation via rods, lugs, angles, and bolts. A gasketmaterial is used between the band and the pipe (figure 31). CMP has a service life ofabout 25 to 50 years. However, depending on reaction to certain soils and waterconditions, there are cases where CMP has deteriorated in less than 7 years.Many embankment dam failures have been associated with the use of CMP conduits.CMP has had a history of joint separations due to differential settlement, jointseparations due to lateral spreading of the embankment dam, and deterioration.Major federal dam-building agencies, including NRCS, and USACE, limit their use ofCMP to low hazard embankment dams. Reclamation does not permit CMP to beused for conduits through their embankment dams. Although CMP has theadvantage of being lightweight and easily installable without the need of heavyconstruction equipment, there are many serious disadvantages.The disadvantages of using CMP for conduits include:• Deterioration has resulted in many embankment dam failures.• Joint separations from differential settlement and embankment dam spreadingcan result in nonwatertight joints.55