Field and laboratory based studies on the hydrolysis of polyester fibres

Hydrolysis is often portrayed as a significant problem in polyester based geosynthetics. Liquids, such as water, provide the H⁺ or OH ^- ions necessary for hydrolysis. The rate of hydrolysis is accelerated by temperature. Analysis of the strength, stiffness and surface profile of exhumed samples of polyester from reinforced structures in the UK and Turkey showed no degradation of the fibres had occurred. A review of soil temperatures measured in reinforced soil applications indicate that a maximum temperature is recorded immediately behind the facing and that further back in the fill the temperature is significantly lower. The maximum temperature recorded behind the facing was never above ambient temperature and in most cases was at least 10 °C below ambient. A design temperature calculated in accordance with ISO TR 20432 (2007) showed good correlation with the maximum temperature measured in the soil backfill. The design temperature never exceeded about 35 °C. Measurements of moisture contents in reinforced structures (Hsuan et al., 2002) did not exceed 5 % in coarse grained, free draining fill and varied between only 20 % and 10 % in fine grained backfills. Natural soils have pH in the range 4.5-6.5. Where values outside of this range occur it is unlikely that they will be maintained for any extended period of time. Analysis of experimental data, conducted in saturated conditions, indicates that hydrolysis of polyester is not a problem for design temperatures in the range 20-40 °C and design lives of 100-120 years in normal soils.