Investigation of the isochrone concept for predicting relaxation of geogrids

Due to the perceived complexity of relaxation tests, the relaxation respons e of geosynthetics has, in the past, been predicted from isochronous curves generated from creep tests. However, the validity of such an approach has not been extensively investigated. Using experimental data from in-isolatio n creep and relaxation tests performed on eleven different geogrids, the va lidity and limitations of using creep isochronous curves to predict relaxat ion response of geogrids has been investigated. Acceptable agreement betwee n predicted and experimental relaxation responses was rather limited, being observed for specimens tested at low initial load levels and for materials exhibiting relatively large creep strains. With minor exceptions, the expe rimentally measured force relaxation was under-predicted by using the isoch rone approach. Nonetheless, it appears that for the geogrids tested, overal l accurate relaxation response cannot be predicted from isochronous curves constructed using creep data.