Petroleum-based geotextiles have been widely used for several decades in road structures to fulfill the separation function. Such geotextiles preserve the characteristics of the subgrade by limiting their contamination by fine materials from the backfill layer. They present an economic and ecological interest by reducing both the thickness of the subgrade and the emission of greenhouse gases during construction and maintenance operations, in particular those generated during the excavation and transport of materials. The use of local biosourced products with a low environmental impact is an opportunity to increase the contribution of geosynthetics to the 2030 Sustainable Development Goals, as defined by the United Nations in 2015, to promote sustainable consumption and production, combat pollution and the depletion of biodiversity. The objective of the GEONAT project is to demonstrate the potential of integrating local natural geotextiles to perform filtration separation functions in replacement of petroleum-based geosynthetics in road structures. Nonwovens made exclusively of hemp fibers, manufactured in France by the company Géochanvre, could be used for such applications. The strategy deployed to achieve this objective involves: - optimizing the performance of the natural geotextiles produced by Géochanvre and developing natural and biological treatments to increase their use in apparently inappropriate environments; - understanding the initial behavior of natural geotextiles and their evolution over time in road structures depending on the characteristics of soils and traffic through their integration into an instrumented test platform representative of various pavement complexes and into real instrumented road structures; - developing accelerated ageing methods in laboratory conditions to estimate the durability and biodegradability of such materials and ensure that their performance longevity is adapted to their application; - assessing their environmental impact compared to petroleum-based geotextiles, using relevant indicators such as greenhouse gas emission, energy consumption and resource preservation... as used in life cycle analyses. This ambitious objective can be reached though the complementarity of a consortium composed by a research laboratory (Univ-Eiffel), a technical center (IFTH), an innovative SME (Géochanvre) and one of the main actors of the road infrastructure construction (Eurovia). A multidisciplinary approach (laboratory-pilot-industry) will be implemented, based on an experimental and modeling approach spanning the material scale to the real-life road scale. The main expectations of this project are to elaborate recommendations to support the prescription, use and application of natural geotextiles in road structures, to provide test methods evaluating initial performance and performance over time, and to develop current standards. These are all essential steps in the field of civil engineering ensuring the transfer of technology and skills to the profession. The outcome of the GEONAT project will also have important economic repercussions by creating wealth for farmers and manufacturers. It will also generate and increase employment in the production sector of natural geotextiles and in the fields of recommendation and technical support. All GEONAT's tools, methodologies and results will support and facilitate further studies to integrate other local fibers into natural geotextiles and contribute to their further development and use in various applications.