Technical Manual: Conduits through Embankment Dams (FEMA 484)

Conduits through Embankment Dams350be understood (figure 194). This evaluation will need to determine how quicklythe damage is occurring and what the likely progression will be. The simplestand most common evaluation technique is by the use of sounding (hammerblows applied to the concrete surface). Experienced personnel using soundingand visual observation can assess indications of the extent of damage. Insmaller conduits, CCTV inspection techniques may be required.Sounding can provide an indication of delaminated or disbonded concrete bylistening for drummy or hollow sounds. For deeper delaminations or fordelaminations with minute separation, placing a hand close to the location ofhammer blows or watching sand particles on the surface can provideinformation. If vibrations are felt or if the sand particles bounce on the surfacethis can be an indication of delamination.Sounding can indicate concrete strength by the sounds created as the hammerhits the surface or by the rebound of the hammer. High strength concrete has adistinct ring as the hammer hits the surface, and the hammer rebounds sharply.Low strength concrete has a dull thud as the hammer hits the surface, and thehammer rebounds only slightly.Concrete cores can be taken from damaged areas to assist with the detection ofsubsurface deterioration. Laboratory testing and pertrographic analysis areneeded to confirm the causes of deterioration.Non destructive testing methods can also be used to assist with the detection ofdamage. These include the Schmidt Rebound Hammer, ultrasonic pulsevelocity, and acoustic pulse echo devices.The extent of damage determined by the above methods should be mappedand the volume of repair concrete computed for preparation of the repairspecifications. In existing conduits that are too small for man entry, CCTVshould be utilized to evaluate the extent of damage.• Evaluate the need for repair.—The need for immediate repair should be closelyevaluated. If the safe operation of the conduit is affected, immediate repairmay be necessary. However, most concrete damage progresses at a slow rate,and early detection and action may be able to slow the rate of deterioration.Early detection may also mean the difference between a repair and completereplacement. Not all deterioration will require repair if it is non safety related.Small hairline cracking on the concrete surface caused by drying and shrinkageusually does not require repair.An important consideration in determining the need for repair is thescheduling. Except in emergencies, many conduits cannot be removed from