Technical Manual: Conduits through Embankment Dams (FEMA 484)

Conduits through Embankment DamsFigure 149.—Incipient sinkhole in an embankmentdam. Eventually, the continued removal of the soil atthe bottom of the cavern would have caused the roofto migrate to the surface of the embankment dam.If the backhoe investigation results in limited information, it may be necessary toperform a major excavation of the embankment dam to ascertain that the entiresinkhole has been found. This investigation may be combined with the actual repair,as long as the excavation plans are sufficiently flexible to allow for complete removalof the sinkhole wherever it is found.In-situ testing has been successful at some sites to look for soft areas or voids. Acone penetrometer testing program has been used. A closely spaced series of testsperformed on a grid pattern can help discern the limits of any soft areas. At othersites, ground penetrating radar has been somewhat successful to help locate someincipient sinkholes that were near the embankment dam crest, but had not yetbroken through to the surface.11.3.4 RepairIf complete replacement of the conduit is chosen as the repair method, then it ismuch easier to repair the embankment dam. If the conduit is repaired by some insitumethod, then the repair of the sinkhole is made more difficult. In both cases,the basic concept is to repair the embankment dam with a material that is as good orbetter than the original material. The material to be used should be selected toperform the same function as the surrounding material. If the repair area is withinthe impervious core portion of the embankment dam, then similar material shouldbe used. Similarly, shell material should also be used in areas outside of the core. If276