Viscoelastic-plastic constitutive model for the creep and stress relaxation characteristics of a geogrid

The existing geogrid constitutive model does not consider its damage effects under high stress. To analyze the mechanical properties (creep and stress relaxation) of geogrids under arbitrary loading history conditions while considering the different creep characteristics of geogrids under different load levels, it is considered that the geogrid exhibits elastic strain, plastic strain, and viscoelastic strain when it is at a low stress level, and a viscoelastic-plastic model that can reflect the attenuation creep under low stress level is established. Furthermore, when the geogrid is at a high stress level, in addition to the strain at a low stress level, the damage effects of the geogrid needs to be considered, and a viscoelastic-plastic damage model reflecting the non-attenuation creep under high stress levels is established. Both models are composed of spring, plastic element, and Kelvin body in series. The research results show that the two constitutive relations of the proposed geogrid can better match the test results under different stress levels and can predict the stress relaxation of the geogrid well. According to the creep curve fitting of the geogrid, the relationship between the critical time and stress change considering the damage of the geogrid can be obtained, and then the stress range that needs to be considered for the damage of the geogrid can be determined; the stress–strain relationship of the plastic element changes in the form of a hyperbola passing through the origin. These results can provide a scientific basis for studying the performance of geogrids under long-term loads and analyzing their creep reduction coefficients.