Technical Manual: Conduits through Embankment Dams (FEMA 484)

Chapter 12—Renovation of ConduitsHDPE joint fusion machines require specialized contractors, and mobilizing them toa construction site can add to the cost of a sliplining project, especially for smallerembankment dams. For some nonpressurized projects in low hazard embankmentdams, an alternative product, such as “Snap-Tite®” may be used. This proprietaryproduct consists of gasketed joint grooves machined onto lengths of standardHDPE pipe. This alternative is not appropriate for use with pressurized conduits,due the possibility of leakage through the gasketed joints. This type of pipe islightweight, and sections of the pipe can be easily handled by three or four workersand a backhoe (figure 179). After the first section of the pipe is inserted into theexisting conduit, the next section is aligned with the first section and the joint islubricated and pulled together with “come-along hoists” and chains wrapped aroundthe liner. As in the usual method of installing HDPE slipliner, the first section of thepipe is tapered to allow the leading edge to ride over irregularities in the existingconduit. The joined sections of pipe can be pulled or pushed into the existingconduit. Pulling from the upstream end is preferred, because in some cases,excessive force used to push the liner from the downstream end has damaged somejoints. The blocking and grouting procedure would be the same as that for fusedHDPE pipe. For further design and installation details, see the manufacture’s data.The primary advantage of using Snap-Tite instead of standard heat-fused HDPEpipe is reduced installation costs, since a fusion machine is not needed.Disadvantages include the high cost of the proprietary pipe (due to the cost ofmachining of the joint grooves) and that the product has a relatively thin wall, so itmay not be suitable under high embankment dams. The product usually consists ofFigure 179.—Sections of proprietary Snap-Tite® pipe can be easily handledwith small equipment.315