Effects of Sustained and Repeated Tensile Loads on Geogrid Embedded in Sand

Design methods for reinforced soil structures under static loading conditions are relatively well established. Little research has been conducted on the behavior of embedded geosynthetics subjected to repeated loadings. Such research is needed to improve the design of reinforced soil structures subjected to traffic and seismic loadings. The study reported here is related to the long-term performance of a geogrid embedded in Ottawa sand under several confining pressures and subjected to various tensile loads. Different magnitudes of sustained and repeated tensile loads were applied to the geogrid incrementally using a pullout device. The confining pressure increased the soil-geogrid interface friction force and thus affected strain distribution along the geogrid length. Creep developed in the geogrid as the applied tensile load increased. The geogrid creep strain rate at a given tension force was found to be independent of confining pressure at the point of this force application, that is, creep can be viewed as an intrinsic property of the geogrid. A rapid pullout failure of geogrid occurred as the applied sustained load approached the ultimate pullout capacity. Conversely, under repeated loading the pullout occurred progressively. The ultimate pullout load and interaction coefficient, C_i, obtained from repeated loading tests were about 20% less than the values obtained from sustained loading tests. This suggests that a C_i smaller than that obtained in static (conventional) tests should be used in structures subjected to dynamic load. Creep under repeated load was smaller than that under sustained load.