Technical Manual: Conduits through Embankment Dams (FEMA 484)

Appendix B—Case HistoriesProject name: St. Louis Recreation Lake Dam (actual name withheld by request ofowner)Location: MissouriSummary: Conduit abandonment by grout injectionIn 2000, a 118-foot high embankment dam was constructed in the St. Louis area tocreate a 325-acre recreation lake. The lake is an integral part in an upscale landdevelopment. When the construction permit application was submitted to the Statefor approval, the designer included a 16-inch diameter PVC diversion pipe in thebase of the embankment dam to prevent impoundment of water while the dam wasbeing built. The construction permit was ultimately approved with the conditionthat the pipe would be filled with grout when the embankment dam was completed.During construction, some foundation problems were discovered that requiredgrouting of the foundation. The contractor was allowed to construct the lowerportion of the embankment dam, and the grouting contractor was allowed to drillthrough it to grout the foundation. During this process, the contractor apparentlyobserved a small amount of grout flowing from the outlet end of the temporary PVCdiversion pipe (However, this was not reported to the State until after a problemwith the pipe was later discovered).As the work on the embankment dam neared completion and it came time toabandon the temporary diversion pipe with grout, the owner (through his designer)requested permission to alter the plans. Instead of filling the pipe with concrete, theowner proposed to retain the pipe and place a valve on the downstream end of thepipe. Their argument was that this would allow them to use the PVC pipe to lowerthe lake level in the future. The state Dam Safety Program balked at this, and itquickly became a contentious issue between the State and the dam owner. In aneffort to assess the condition of the PVC pipe prior to making a final decision theState used a remotely operated video camera to examine the interior of the pipe.With the owner and his engineer present, a video camera was inserted into thedownstream end of the pipe. At approximately 450 feet upstream of the pipe outlet,a separated joint was observed (figure B-70). Just upstream of that joint, the pipehad collapsed, leaving a space only a few inches high at the bottom (figure B-71)The pipe was immediately abandoned by completely filling it with grout.The owner later admitted that if the State had not been able to demonstrate why itdid not want a valve on the downstream end of the pipe, he would have tried tocoerce the State to allow the pipe to remain by contacting his legislators or by goingB-91