Geosynthetics have been widely used since 1970 in unpaved roads. Various research studies showed the benefits of the reinforcement in facilitating the fill material compaction, improving the platform bearing capacity, which will allow the reduction of the fill material thickness, and the increase of the structure serviceability term. Different mechanisms take place between the aggregates platform and the reinforcement. Which affect the structural behavior: the aggregates platform confinement, the separation between the weak subgrade and the fill material, the membrane effect. The road structure becomes even more heterogeneous and the mechanisms more complex with the addition of the reinforcement layer and the underlying mechanics are still not completely understood. Therefore, it is important to provide more knowledge regarding these mechanisms, in order to propose an efficient design method for such structure.

A full-scale laboratory test on unpaved roads has been designed and developed to characterize the effect of the reinforcement in this application. The platform tested is placed in a large box of 5 m in length, 1.9 m in width and 1.4 m in height. The tested platform is composed of 0.6 m of weak subgrade supporting 0.22 m of well-compacted fill material. A special attention has been given to the soil layers preparation, installation and quality control. The tested structure was subjected to a cyclic load to simulate traffic using a large-scale apparatus SAT (Simulator Accelerator of Traffic). This apparatus was developed and adapted for this flexible structure. Indeed, it allows the application of a heavy traffic load on the unpaved road surface even for large surface displacement. During each test, the rut development, the vertical stress distribution and the settlement in the subgrade soil are monitored. Moreover, the optical fiber technology is used to measure the strain developed in the reinforcement layer.

An unreinforced platform has been first tested serving as a reference, and different geosynthetic reinforcement types were tested. The results are presented in terms of vertical stress distribution on the subgrade surface, and vertical stress and ruts evolution with cycles. The results were used to compare the benefit of the different geosynthetic types and discuss the dominant developed mechanism. Moreover, a numerical simulation has been developed and calibrated based on the results of these experiments using FLAC3D®.