Technical Manual: Conduits through Embankment Dams (FEMA 484)

Conduits through Embankment DamsThese materials are discussed in the following sections.2.1.1 Reinforced cast-in-place concreteReinforced cast-in-place concrete is placed and allowed to cure in the location whereit is required to be in the completed conduit. Reinforced cast-in-place concrete ismade by mixing cement, fine and coarse aggregates, sand, and water. Admixtures arefrequently added to the concrete immediately before or during its mixing to increasethe workability, strength, or density, or to lower its freezing point. A framework ofreinforcing steel is constructed, and forms to contain the wet concrete mix are builtaround the reinforcement. The wet concrete mix is placed inside the forms andaround the reinforcing steel. Typically, consolidation of the concrete mix is obtainedby vibration. The final solidified mass becomes reinforced cast-in-place concrete.Reinforced cast-in-place concrete conduits are built at the construction site.Figure 21 shows typical reinforcement used with cast-in-place concrete.Reinforced cast-in-place concrete conduits (figure 22) have a long history of use bythe major dam design agencies. Reinforced cast-in-place concrete conduits are veryadaptable in their application and can be designed to fit specific project requirementsand site conditions. A variety of design shapes are possible. For guidance onselecting the proper shape see section 4.1. Properly designed and constructedreinforced cast-in-place concrete should have a service life of 100 years or longer.The advantages of using reinforced cast-in-place concrete for conduits include:• The longitudinal reinforcement typically extends across the conduit joints. Thisprevents the joint from separating and developing a leak.• A variety of conduit shapes are available to provide better distribution ofloadings to the foundation.• Conduit shapes can be designed to provide for good compaction of earthfillagainst the conduit.• Allows for redundant seepage barrier protection, since waterstops andreinforcement typically extends across conduit joints. Welded steel liners areoften used to provide additional seepage barrier protection.The disadvantages of using reinforced cast-in-place concrete conduits include:• Construction costs are often higher than for other conduit materials,particularly for small diameters.42