Geotextiles in Embankment Dams - Association of State Dam Safety ...

Chapter 2—Overview of Geosynthetics for Use in Embankment Dams2.10.2 Polymer typesAccording to Koerner (2005a), geotextile fibers are manufactured from the followingbasic polymer groups:• Polypropylene (PP) 92% of geotextiles• Polyester (PET)• Polyethylene (PE)• Polyamide (Nylon)5% of geotextiles2% of geotextiles1% of geotextilesThe majority of nonwoven or woven geotextiles presently available for use in damconstruction are manufactured of polypropylene fibers. Detailed information on thephysical properties of individual polymers and the resulting fibers used in geotextileproduction can be found in Koerner (2005a), Van Zanten (1986), and Ingold andMiller (1988).Polypropylene (PP) fiber is a semi-crystalline thermoplastic olefin produced bypolymerizing propylene monomers in the presence of a catalyst. Two types ofpolypropylene are the homopolymers and the copolymers. The more rigidhomopolymers are predominantly used in fiber production. Polypropylenehomopolymers for geotextile production are specifically designed to meet both thestringent processing and final end-use strength and durability requirements.Polypropylene fiber is produced by melt spinning the molten polymer, followed bystretching to orient the fiber molecules. Special additives including antioxidantpackages and thermal stabilizers and UV packages are used to protect against ageing.A life expectancy of a minimum of 200 years can be expected from properlystabilized and protected polypropylene geotextile fibers in buried applications (VanZanten, 1986).Polyester, generally known as polyethylene terephthalate (PET), is a manufacturedfiber produced by polymerizing ethylene glycol with dimethyl terephthalate orterephthalic acid. Various additive packages are used to increase the speed ofpolymerization as well as antioxidants and thermal stabilizers to reduce degradationduring production and ageing. Properly stabilized polyester in a coveredenvironment will have a very long life expectancy. Polyester fibers have highstrength and are resistant to shrinking and stretching (creep). Polyester fiber must beprotected from aggressive alkaline environments.Polyethylene (PE) fiber is made of 97-98% pure polyethylene resin usually inmonofilament form. Ethylene is polymerized at high pressures and the resulting35