Technical Manual: Conduits through Embankment Dams (FEMA 484)

Conduits through Embankment DamsFigure 176.—Completed HDPE slipliner in existing CMP spillway conduit.Photo courtesy of Maryland Dam Safety Division.If the HDPE slipliner experiences some type of damage over the long term, thedamage should be assessed by trained personnel using man-entry or CCTVinspection methods as discussed in section 9.5. Repair of HDPE pipe afterinstallation and grouting is completed is not practicable for the buried sections ofpipe. Very little can be done to effectively repair the existing HDPE slipliner inburied sections of pipe within the embankment dam. However, another HDPEslipliner of smaller diameter can usually be inserted and grouted in place. Sections ofHDPE pipe that are exposed and accessible may be repaired by cutting out thedamaged section and replacing the entire section of pipe. Further guidance onreplacement and methods available for joining pipe are provided in CPChem’s ThePerformance Pipe Engineering Manual (2003).For examples of projects that have utilized HDPE sliplining, see the case histories inappendix B for Round Rock and Twin (Turtle) Dams.Alternatives to sliplining existing conduits with solid walled HDPE pipe.—Anewer application of HDPE pipe for sliplining existing conduits involves the use ofdual containment HDPE pipe. This application is recommended, if the HDPEslipliner is to be pressurized. Dual containment HDPE pipe is manufactured as twoseparate HDPE pipes and assembled by placing one inside the other. The insidepipe (containment pipe) is centered within the outer pipe (carrier pipe) with endspacers (centralizers) located at each end of a section of pipe. The end spacers arefabricated for a tight fit and are extrusion welded to the dual wall containment pipe.312