1995-09-08_GENERAL DOCUMENTS - M1977493

Home Browse Search

Cutoff Collars The cutoff collars will be conventional concrete cutoff walls designed to increase the seepage path along the outlet conduit by at least 20 percent. The concrete cutoff wall design is based on the design recommendations included in TR-46 and the State's requirements. Each collar will extend two feet beyond the sides of the pipe and cradle, providing a total increase in the seepage path of 4.5 feet per collar. Installation of six collars will increase the seepage path within the impervious zone of the dam (Zone 1) by 22 percent. Each collar will be separated from the reinforced concrete pipe by %-inch preformed bituminous joint filler to prevent the transfer of external loads from the collars to the pipe. Outlet Headwall Drain Ten feet of slotted polyvinyl chloride (PVC) pipe will be placed on each side of the outlet conduit at the discharge end for purposes of draining water collected behind the headwall. The drain pipe discharges through the headwall and into the downstream channel. Also, 4-inch diameter PVC will tee into the drain pipe for purposes of conveying seepage flow around the headwall and discharge into the crotch of the dam outside the discharge channel. Because the drain pipe is located above the embankment seepage blanket, it is anticipated that very little water introduced as seepage through the dam will be collected within the drain pipe system. If seep water is discharged from the drain pipe during operation of the reservoir, the water will be monitored and tested to determine if the quality is acceptable for release downstream. If the seep water is found to be acceptable, the pipe routed around the headwall will be plugged to force the seep water to discharge into the downstream channel. Otherwise, additional pipe will be placed from the headwall to the existing seep collection pond at the toe of the embankment for purposes of isolating and capturing seep water. 10