Technical Manual: Conduits through Embankment Dams (FEMA 484)

Chapter 9—Inspection and Assessment of Conduit-Related ProblemsFigure 133.—Pressure washing cleaning head.Again, it should be strongly emphasized that any cleaning should be givenconsiderable thought before proceeding, to avoid causing any damage, or worseningexisting defects within the conduit.In some situations, minor cracks or joints experiencing seepage may eventually sealthemselves by calcite deposition. This process occurs when calcite precipitates outof solution and forms a deposit. Deposition may occur as the seepage evaporates,leaving the calcite behind. Calcite deposits typically mineralize and harden over time.Figure 134 shows a conduit joint where calcite deposition has sealed a minor leak. Ifinspection shows locations within a conduit where this has occurred, cleaning withhigh pressure could remove enough of the calcite deposition to cause seepage tobegin again. This possibility needs to be carefully considered prior to performingany cleaning operations within the conduit.9.7 Forensic investigationTo better understand and to provide further knowledge concerning the failuremechanisms resulting from the internal erosion or backward erosion piping within anembankment dam, forensic investigation should be considered. Althoughtraditionally a forensic investigation is conducted to establish the failure mechanismfor legal cases, a detailed investigation can be very helpful in determining the causesof failures and to provide insight into design changes to reduce failures in the future.For projects where a failed conduit is being removed and replaced, closecoordination between designers, embankment dam owner, and the contractor will berequired to preserve the soil adjacent to the conduit. The investigation team should231