Technical Manual: Conduits through Embankment Dams (FEMA 484)

Conduits through Embankment Dams(approximately 50 to 100 years) than concrete, but may be preferred in situationswhere aggressive water or soil chemistry could attack concrete.Plastic pipe consists of resins composed of polymerized molecules mixed withlubricants, stabilizers, fillers, and pigments. Plastic pipe used in the construction orrenovation of conduits has included thermoplastic and thermoset plastic. Thesematerials are discussed in the following sections.2.2.1 ThermoplasticThermoplastics are solid materials that change shape when heated. Thermoplasticscommonly include polyethylene (PE) and polyvinyl chloride (PVC). Thermoplasticpipe is produced by the extrusion process. The extrusion process continuouslyforces molten polymer material through an angular die by a turning screw. The dieshapes the molten material into a cylinder. After a number of additional processes,the final product is cut into the specified pipe lengths.The advantages of using thermoplastic pipe as a new conduit or for the sliplining ofan existing conduit include:• Lightweight material that facilitates installation.• Resists corrosion and is not affected by naturally occurring soil and waterconditions. May be preferable in certain conduit applications where aggressivewater or soil chemistry would limit the life of concrete or metal pipe.• The smooth interior surface reduces friction loss. Also, due to the very smoothsurface of thermoplastic pipe, adherence of minerals (e.g., calcium carbonate) isminimized.• The ability to heat fuse PE pipe joints provides a watertight joint.• Resists biological attack.The disadvantages of using thermoplastic pipe as a new conduit or for the slipliningof an existing conduit include:• High coefficient of thermal expansion relative to concrete can cause movementof the slipliner, requiring the use of end restraints.• Can easily be damaged or displaced by construction and compaction equipmentunless it is encased in concrete.46