The technique of ground improvement using geogrid reinforcement in roadway applications started in the 1970s. Geogrid reinforcement has been increasingly used in the construction of roadways, nowadays. It is clear from the literature that geogrids can reduce permanent displacement (rutting) and base course thickness and extend the service life of a pavement. In this study, the effects of geogrid reinforced unpaved roads on weak subgrade was investigated by conducting large scale laboratory tests under cyclic loading. Large scale cyclic plate load test equipment was developed for this purpose. Using this test setup, performance of base and subgrade soil under cyclic loading test conditions were evaluated. In large scale tests, cyclic loading at a fixed frequency was applied with 300 mm diameters of circular plate. The results of this paper showed the benefits of the geogrid reinforcement and effect of the base layer thickness. It was observed that, geogrid reinforcement improve the performance of the base course layer and protecting/stabilizing the subgrade layer, thus reducing the pavement’s permanent displacement (rutting) under cyclic loading. In summary, permanent settlement decreased with both of increasing the base course thickness and using the geogrid reinforced in base course layer.
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