Technical Manual: Conduits through Embankment Dams (FEMA 484)

Conduits through Embankment DamsFigure 134.—Calcite deposition has sealed this leak at aconduit joint.consist of experienced geotechnical and civil engineers, geologists, surveyors, andconstruction personnel. All anticipated items of interest (e.g., voids) should beclearly communicated to all parties involved prior to the commencement ofembankment excavation. Test pits are usually excavated along the conduit,extending a specified depth below the bottom of the conduit. The contractor musttake care to prevent damage to in-situ conditions before the investigation team candocument them. Figure 135 shows an outlet works conduit excavation during aforensic investigation. Figure 136 shows how polyurethane grout flowed throughthe backfill surrounding an outlet works conduit during joint sealing operations.Close coordination between the forensic team and contractor were required in orderto preserve this information for study.Documentation of the conditions encountered is essential to be able to recreate theevents leading to the failure. A surveyor with a transit, theodolite or total station,and one or more assistants with survey rod or reflector target should be available toprecisely document the location (position and elevation) of items of interest.Numerous photographs should be taken, even of items that do not appear to havecontributed to the failure in case they are needed later, since the soil structuresurrounding the conduit will likely be destroyed by the investigation and theinformation will be forever lost, if not carefully documented.A JHA should be prepared for all onsite forensic investigations. See section 9.4 fordetails on preparing a JHA. For details of a forensic investigation, see the AnnapolisMall Dam case history in appendix B.232