Technical Manual: Conduits through Embankment Dams (FEMA 484)

Chapter 9—Inspection and Assessment of Conduit-Related ProblemsProblems common to terminal structures include deterioration, damage,obstructions, misalignment, backfill and foundation deficiencies.Descriptions of more specific problems related to basin, chute blocks, baffle blocks,or end sills are beyond the scope of this document. The TADS program, asdiscussed earlier in this chapter, should be referred to for more detailed informationconcerning the inspection of terminal structures.9.5.4 Specialized inspectionSpecialized inspection includes the use of a dive team, climbing team, remotelyoperated vehicle (ROV), or closed circuit television.9.5.4.1 Underwater inspectionsUnderwater inspection is typically accomplished by either scuba diving operations orsurface-supplied air diving operations. Scuba diving equipment typically includes abreathing gas supply tank, which is carried by the diver. A scuba diver has moreflexibility and maneuverability compared to surface-supplied diving operations.However, this method of inspection limits diver communication and should belimited to areas where the diver has an unobstructed path directly to the surface.Surface-supplied diving operations provide breathing gas to the diver via anumbilical and offer deeper dive capability, the potential for longer underwater stays,and communication between the diver and the surface, and should be utilizedwhenever the diver enters an overhead environment (diver does not have a directvertical path to the surface).Dive inspections are used for the examination of conduits, and entrance and terminalstructures. However, the focus of this section will pertain only to dive inspections ofconduits. The inspection of a conduit is often termed a “penetration dive.”Dive inspections are expensive, and the costs are greatly influenced by the depth ofthe dive, the elevation at which the dive is performed, and the temperature of thewater. All specialized inspections involve a number of variables. As a general a ruleof thumb, when comparing the costs involved with dive inspections to ROVinspections, dive inspections are about 3 to 5 times more expensive.A dive inspection has the advantage of using a variety of instruments for testing thestructural integrity of the conduit, such as a rebound hammer for providing data onconcrete surface hardness, a magnetic reinforcing steel locator to locate and measurethe amount of concrete cover or reinforcement, and an ultrasonic pulse velocitymeter to determine the general condition of concrete based on sound measurements.Dive inspections also offer the potential for hands-on, tactile inspection of featuresin limited visibility or those covered with shallow layers of organics or sediments.213