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Unbound base courses are subject to high cyclic-dynamic stresses resulting from traffic loads. As they cannot absorb tensile forces, they can be reinforced if necessary. Field experiences have shown that the use of geosynthetics improves the trafficability of unpaved roads on soft subsoil. Specifi-cally, the thickness of the base course and therefore the amount of high-quality geomaterials, e.g. crushed gravel, can be reduced. There are extensive studies throughout the literature that confirm the mechanism of the bearing capacity improvement, concentrating on individual effects such as the influence of the bear-ing layer thickness at constant subsoil strength. To clarify the influence of the reinforcement and to inves-tigate the effectiveness of different geosynthetics in unpaved roads, field measurements, systematic labor-atory as well large-scale tests and cyclic triaxial tests were carried out. Beside the bearing strength and stiffness of the soft subsoil, the base course thickness as well as the type, and hence the tensile and struc-tural stiffness have been found to dominate (beside the granular material itself) the overall behavior of the stabilized base course material. Under the identified stress and deformation conditions, controlled tests show that the reinforcement reduces the plastic deformations by more than 30 % and thus influences the serviceability significantly.