Technical Manual: Conduits through Embankment Dams (FEMA 484)

Chapter 2—Conduit Materials• Compaction of earthfill is difficult under the haunches of the pipes unlessencased in concrete to provide good compaction of earthfill against the conduit.• Heat fusion of pipe joints requires special equipment and an experiencedoperator.• Requires a concrete encasement for significant and high hazard embankmentdams to provide a favorable shape for compaction of earthfill against theconduit.Solid wall, high density polyethylene (HDPE) is the most commonly usedthermoplastic material for sliplining of existing conduits. Figure 24 shows anexample of HDPE pipe. HDPE pipe is an inert material and as such is not subjectto corrosion or deterioration, has a long service life, and requires little maintenance.This is especially important in small conduits that are not easily renovated andcannot be easily inspected. HDPE has been used in sliplining of existing conduits,since the early 1980s. HDPE is typically available in sizes up to 63 inches indiameter. The manufacturer can fabricate HDPE pipe fittings, such as bends,flanges, reducers, and transitions. Specialized fittings can also be custom fabricated.HDPE pipe is typically black. However, HDPE pipe is also available with gray andwhite pigmentation to reduce glare and improve conduit inspection using closedcircuit television (CCTV) equipment. For guidance on the use of HDPE pipe inconduit sliplining applications, see section 12.1.1.PVC pipe (figure 25) is not as commonly used as HDPE pipe as a conduit orslipliner due to concerns with lack of watertightness and other inherentdisadvantages. The major disadvantage with PVC pipe is the bell and spigot jointconnections. This type of joint connection has the potential for leakage or canseparate as the embankment dam settles. The bell and spigot joint integrity must betested for leaks to ensure that the gasket has not rolled off during installation. Use ofPVC bell and spigot joints should only be considered for nonpressurized, low hazarddam applications. PVC is typically available in sizes up to 48 inches in diameter.Figure 24.—HDPE pipe to be used for sliplining of an existing conduit.47