Technical Manual: Conduits through Embankment Dams (FEMA 484)

Chapter 4Structural Design of ConduitsConduits through embankment dams differ from nonwater-retaining structures.Conduits have many unique structural design requirements, which the designer mustconsider in any design. These requirements include:• Cracking must be minimized to avoid the effects of internal erosion andbackward erosion piping. Minimizing cracking will also reduce the vulnerabilityof reinforcement corrosion. Also, conduits located on weak or compressiblefoundations must remain watertight during horizontal and vertical movementscaused by settlement and spreading of the embankment dam.• High velocity flow can result in cavitation or erosion.• Flow within conduits can fluctuate over the year, depending on projectrequirements.• Due to the release requirements of the downstream users, conduits may bedifficult to shut down for frequent maintenance or repair.• Tight tolerances are required to maintain properly functioning gates and valves.The following sections discuss some of the important aspects to consider in thestructural design of the conduit. For additional guidance on the structural design ofconduits, see Reclamation’s Design of Small Dams (1987a), and USACE’s StructuralDesign and Evaluation of Outlet Works (2003b) and Culverts, Conduits, and Pipes (1998a).4.1 Conduit shapeThe primary considerations in selecting the proper shape of the conduit are:• To promote good compaction of earthfill against the conduit75