Technical Manual: Conduits through Embankment Dams (FEMA 484)

Contents117 This conduit was severely damaged after the foundation settled morethan 2 feet .....................................................192118 Visual inspection for seepage on the downstream face of an embankment dam ..........................................................195119 Sinkhole in the crest of an embankment dam.........................207120 Sinkhole around a spillway riser . . . . . . . . . . . . . . . . . . ..................207121 Inspection of a CMP conduit looking for signs of deterioration .......... 210122 Inspection being performed in difficult conditions. The joints of this 48-inconcrete pipe separated when foundation movement occurred duringconstruction of the embankment dam. For details, see the case history forLittle Chippewa Creek Dam in app. B ..............................210123 Diver performing an under-water inspection .........................217124 Climber performing an inspection on a terminal structure wall ........... 218125 An observation-class ROV entering the water to begin an inspection ..... 219126 Seepage entering a CMP conduit through a defect.....................222127 Corrosion within a 24-inch-diameter CMP outlet works conduit ......... 222128 A CCTV inspection camera-crawler entering the downstream discharge portal of an outlet works conduit ..................................223129 Camera-crawler used for CCTV inspection of conduits ................. 223130 Most CCTV inspection equipment is portable and can be carried to conduit access locations ..........................................225131 A small color video camera used for CCTV inspection .................225132 A joint has separated in the steel pipe of this outlet works ..............228133 Pressure washing cleaning head ....................................231134 Calcite deposition has sealed this leak at a conduit joint ................ 232135 An outlet works conduit is being excavated during a forensic investigation. The top of an antiseep collar is exposed on the left side ofthe figure ......................................................233136 Close coordination between the forensic team and contractor allowed forcareful study of how polyurethane grout injected into the deterioratedjoints of a conduit flows through surrounding backfill. In this case, theforensic investigation showed the injection of grout was relativelysuccessful in sealing the joints of the conduit .........................233137 The perimeter of a wet area at the downstream toe of an embankment damlocated with wooden stakes .......................................240138 Seismic tomography being used on an embankment dam ............... 247139 Seismic tomography profile along failed CMP spillway conduit in anembankment dam ...............................................249140 Typical section from seismic tomography used to identify voids along theoutside of a CMP spillway conduit in an embankment dam . . . .......... 249141 Collecting self potential (SP) data on the crest of an embankment dam inVirginia to trace the source of observed seepage. The 75-ft highembankment dam had a sinkhole, a sand boil, and several seepage pointsxxi