Technical Manual: Conduits through Embankment Dams (FEMA 484)

Conduits through Embankment DamsFigure 72.—Special design considerations are required in locations wheredifferential settlement between two structures can occur.Chapter 2 discussed materials used for the construction of conduits, such asreinforced cast-in-place concrete, precast concrete, plastic, and metal. The followingsections provide guidance pertaining to joints used with these types of materials.4.3.1.1 Reinforced cast-in-place concreteReinforced cast-in-place concrete conduits undergo physical changes in length,width, height, shape, and volume when subjected to environmental and mechanicalconditions surrounding them (USACE, 1995e, p. 2-1). These changes may be theresult of drying shrinkage, creep, settlement, and other effects. As these changesoccur, internal stresses may form within the concrete, resulting in cracking. Mostreinforced cast-in-place concrete conduits require joints to control or limit crackingand are typically placed in conduits about 12 to 16 feet apart. The location of jointscan also be utilized to facilitate construction.Four types of joints are commonly used in construction of reinforced cast-in-placeconcrete (Reclamation, 1987a, p. 799):102• Contraction joints.—Contraction joints are used in concrete to provide for thevolumetric shrinkage of a monolithic unit or movement between monolithicunits. These joints provide for a complete separation of the monolithic unitinto smaller structural elements. No bond is expected between the concretesurfaces of the smaller structural elements. Sealing (curing) compound appliedto the joint surfaces can be used to prevent bonding. Except as otherwise