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Geosynthetics have been widely used since 1970 in unpaved roads. Various research studies showed the reinforcement benefits 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 600 mm of weak subgrade supporting 220 mm or 350 mm 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 plate load and to a circulation traffic load 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 were monitored.
In the present paper, the results of the cyclic plate loading tests are presented. In fact, six tests were performed, two reinforced and unreinforced platforms with 350 mm of base course thickness, and four reinforced and unreinforced tests with 220 mm of base course thickness were performed.
The results are presented in terms of vertical stress distribution on the subgrade surface, and vertical stress and ruts evolution with cycles. The results allowed the verification of the experimental protocol repeatability and the comparison between the reinforced and unreinforced platform with different base course thicknesses. In fact, the results of these first tests allowed the protocol preparation for further tests using the SAT apparatus.