Technical Manual: Conduits through Embankment Dams (FEMA 484)

Chapter 4—Structural Design of Conduitsneeded with any shape of conduit selected. A filter provides adefense against internal erosion and backward erosion pipingresulting from differential settlement of the conduit, hydraulicfracture of the embankment, or deterioration of the conduit.See chapter 6 for guidance on the design and construction offilters.In some special situations, double or triple barrel conduits maybe required. Operational and/or flow capacity requirementsusually determine the number of barrels required. StructuralFigure 52.—Conduitshape Gdesign of multibarrel conduits should adhere to the guidance in this section. Figure53 shows an example of a double barrel conduit under construction.The following sections discuss conduit shapes that have been used by the majorembankment dam design organizations.4.1.1 Conduit shapes A, B, and CConduit shapes A, B, and C (figures 46-48) tend to be less adaptable to changes inloading and stresses than fully circular sections, but provide an exterior surface thatis superior for compacting earthfill materials against. Depending on the loading,stress concentrations may be large enough in or near the base that shear stirrups maybe required or concrete thicknesses must be increased.Figures 54, 55, and 56 show the interiors of conduit shapes A, B, and C, respectively.Conduit shape A is typically used for pressure flow. Conduit shapes B and C aretypically used for nonpressurized flow conditions. Conduit shapes B and C are alsoused as the larger downstream access conduit in arrangement 1, as discussed inFigure 53.—A multibarrel outlet works conduit under construction.77