Report No. : GEO Report No. 37

Report Title : Creep, Stress Rupture and Hydrolysis of Polyester Geogrids (1995), 67 p.

Author : J.H. Greenwood

Abstract

This report reviews the state of knowledge of creep, stress rupture and hydrolysis of polyester geogrids at the time of writing. There is a considerable amount of creep strain data on polyester yarns, extending to 90000 h (10.5 years) duration, but data for specific geogrids are limited. There are no published creep-rupture data measured directly on geogrids, apart from some ongoing long-term creep tests. Test results obtained on yarns suggests that in accordance with the kinetic theory of fracture, a design life of 120 year corresponding to a strength of 50-55% of index breaking load.

The temperature dependence of both creep and creep-rupture for polyester is slight. The soil will reduce creep by transferring load to the reinforcing fibres through frictional forces on the sheath and by interlocking with the transverse bars. The hydrolysis of polyester fibres in water and the resulting reduction in molecular weight and strength have been shown to be due to chemical process whose rate of reaction can, given sufficient data, be extrapolated to a selected service temperature. An alkaline environment above pH 10 causes additional chemical attack. There is still much controversy concerning the hydrolysis of polyester.

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