Technical Manual: Conduits through Embankment Dams (FEMA 484)

Conduits through Embankment Dams• Risk.—The development of small defects within the conduit can lead to seriousfailure modes threatening the entire embankment dam. Designs needs to berobust and conservative.• Movement.—Conduits within high embankments dams, built on compressiblefoundations, may experience significant displacement as the dam settles. Theconduit joints need to be capable of absorbing such movements whileremaining watertight. The conduit placement needs to anticipate subsequentsettlement in order to remain positively sloping for gravity drainage.Inexperienced designers may inadvertently apply inappropriate design standards ormisuse design standards to save on time and provide cost savings. Examples of themisapplication of design standards include:• Inappropriate design references.—State highway department standard plans forculverts and culvert structures are sometimes simply referred to in constructionspecifications and drawings to save the designer from actually designing theconduit. Culvert designs are not intended for use within embankment dams.• Inappropriate application of standards.—The NRCS has developed severalstandardized conduit and joint detail drawings for use in embankment dams.Such drawings have been used to successfully build thousands of smallembankment dams. Such drawings have also been misused. In one knowncase, the standard detail drawings were used to unsuccessfully install apressurized conduit on a high hazard embankment dam on a soft foundation.As with all standardized designs and drawings, the design and constructionassumptions made in preparing the drawings need to be satisfied for the specificapplication and site.• Inappropriate use of materials.—Reinforced concrete pressure pipe has been usedfor pressurized conduits within embankment dams. Reinforced concretepressure pipe utilizes gasketed joints, which could be subject to leakage, ifimproperly constructed. In a typical 100-foot high embankment dam therecould be over 80 gasketed joints, all with the potential for leakage.Conduits often penetrate other types of embankment structures or are used forutility purposes. These types of penetrations are not addressed in detail in thisdocument. Some of the guidance presented in this document may apply to thesetypes of penetrations and should be carefully evaluated by designers forimplementation. Users of this document will need to evaluate the applicability of theproper guidance to their project. Conduit penetrations not specifically addressedwithin this document include:22