Technical Manual: Conduits through Embankment Dams (FEMA 484)

Conduits through Embankment DamsFigure 16.—Good compaction around antiseep collars was difficult toachieve.embankment dam design. See chapter 6 for guidance on the design and constructionof filters. Since filters have become a standard design element in embankment damdesigns, very few failures have occurred that can be attributed to internal erosion orbackward erosion piping near conduits.1.2 Locating the conduitA number of factors influence the layout of a conduit, such as the type and crosssection of the embankment dam, topography, geology, and hydraulics. Conduitsthrough embankment dams are often referred to as “cut-and-cover” conduits.Conduits through embankment dams should be avoided, when safe andcost-effective alternatives are available. An alternative to a conduit through theembankment dam is a tunnel located in the abutment, wherever geology, topography,and economics are favorable. The advantages of a tunnel include:• Eliminates potential failure modes.—The tunnel is not physically associated with theembankment dam. Using a tunnel completely eliminates the potential failuremodes normally associated with a penetration through an embankment dam.• Facilitates construction.—A tunnel can often facilitate stream diversion around thedamsite during construction.• Simplifies embankment placement.—A tunnel can allow unobstructed embankmentplacement, since it no longer hinders construction of the earthfill.34