A section of a German motorway (autobahn) has to be relocated. The new route crosses an old closed waste disposal. This old landfill contains heterogeneous unsorted non-compacted materials, some of them including toxic components. The waste was completely insulated from the environment by a capping system twenty years ago. The fixed gradient of the new route cuts the capping system, i.e. construction had to take place on the waste, the latter being problematic due to many reasons. Ideally this should be avoided, but then two requirements have to be met: on the one hand the motorway bearing layers should be as thin as possible to avoid waste contact; on the other hand their deformability has to be low enough to equalize differential settlements due to the waste heterogeneity below. A promising solution was the application of high-strength, high tensile stiffness geosynthetic reinforcements to stiffen the system: this is the objective of this publication. Multiple design studies have been performed based on analytical procedures in the German reinforcement Code EBGEO and in the British reinforcement Code BS 8006. Some of them had to be modified and further developed. Totally four methods were used. The final solution includes knitted geogrids from Aramid (AR) and laid/welded geogrids from high-tenacity Polyester (PET). The paper describes and comments the problems, the search for an optimized solution, the design methods and modifications applied, the final solution with the corresponding reinforcements and some execution aspects.