Technical Manual: Conduits through Embankment Dams (FEMA 484)

Chapter 8Potential Defects Associated with ConduitsDefects associated with conduits can lead to the development of potential failuremodes. If corrective action is not taken to repair the damage resulting from thedefect, this can lead to a failure of the embankment dam. For a further discussion ofpotential failure modes associated with conduits, see chapter 7. For guidance on therenovation, removal and replacement, and repair of conduits, see chapters 12, 13,and 14.Various materials have been used in the construction of conduits, such as concrete,plastic, and metal. Each conduit material reacts differently in embankment damapplications. A search of the USACE’s Waterways and Experiment Station damageand repair data base indicated that the most common defect requiring repair inconcrete conduits was leakage through cracks and joints (USACE, 1988, p. 96).This chapter will discuss some of the most common types of defects associated withconduits. Periodic inspection of the conduit by man-entry or CCTV inspection isthe only reliable method to detect the extent of damage. For guidance on inspection,see chapter 9.8.1 DeteriorationOften, if deterioration is left unchecked, it will continue and progressively worsen. Ifrepairs are promptly made, the conduit may be able to continue to function in aserviceable fashion. However, if deterioration is allowed to progress, there maycome a time when a significant portion of the conduit must be entirely replaced.Action for timely repair may be more cost effective than postponing repairs andeventually having to replace major portions of the conduit.8.1.1 AbrasionAbrasion in conduits is an erosional process and is a function of velocity andturbulence in the flow, the hardness of the abrasive material, and the quality of thesurface experiencing abrasion. Abrasion is caused by water flowing through aconduit at high velocities and containing silts, sands, gravels, or stones (figure 105).177