Technical Manual: Conduits through Embankment Dams (FEMA 484)

Conduits through Embankment Damsjustified based on extremely favorable soil conditions, good conduit constructionmaterials and methods, reliable construction practices, and favorable foundationconditions.4.2.3 MetalAs discussed in the previous section, NRCS’s Structural Design of Flexible Conduits,(2005) provides design guidance for flexible pipe materials, including metal andplastic. In general, the following guidance should be considered for conduits usingmetal pipe:• Steel pipe.—Steel pipe should be designed in accordance with industry acceptedmethods, such as found in AWWA M11 (2004), Amstutz (1970), and Jacobsen(1974). For guidance on the design of steel pipe used within conduits, seesection 12.1.2.• CMP.—CMP should only be used for nonpressurized applications in lowhazard embankment dams. CMP should be designed in accordance withindustry-accepted methods as found in the American Association of StateHighway and Transportation Officials’ (AASHTO), Standard Specifications forHighway Bridges (2002) or the American Iron and Steel Institute’s (AISI),Handbook of Steel Drainage and Highway Construction Products (1994). USACE’sCulverts, Conduits, and Pipes (1998a) provides guidance for CMP used in rurallevee systems and drainage culverts. Certain aspects in that reference may applyto CMP used in low hazard embankment dams.Metal pipe used within low hazard embankment dams is often not encased inreinforced cast-in-place concrete. However, as discussed previously with plasticpipe, the use of a filter diaphragm or collar is a valuable defensive design measure,even for low hazard classification embankment dams with favorable site conditions.4.3 WatertightnessThe major dam-building agencies require conduits within an embankment dams tohave watertight joints. The degree of water tightness depends on the anticipatedhydrostatic head either inside or outside of the conduit. For example, pressurizedreinforced cast-in-place concrete conduits are waterstopped and have longitudinalreinforcement extending across the joint. In some cases, a welded steel liner may beused for additional protection. The following sections discuss guidance pertaining tothe watertightness of concrete conduits. Plastic and metal pipe are frequently used inthe renovation of existing conduits; for guidance on watertightness using thesematerials, see chapter 12.98