The present highway (Autobahn) bridge on the German Autobahn A1 over the river of Rhine near Cologne will be replaced by a new one due to increasing heavy traffic. Because of that a section of one kilometer of the present Autobahn A1 approaching the bridge has to be relocated. The new route crosses an old closed waste disposal; there are no other options due to the surrounding property.

The landfill has been under operation from the 50ies until the 80ies. It contains heterogeneous unsorted non-compacted materials from that time, some of them including toxic components. After closure twenty years ago special measures found place to insulate it completely from the environment.

Unfortunately, the gradient of the new A1 route cuts the landfill capping system, i.e. construction has to take place on the "naked" waste with strictly speaking unknown degree of contamination at any point of the one kilometer route and varying mechanical behavior in both longitudinal and cross-route directions as well.

Two controversial requirements have to be met: on the one hand the intervention into the waste has to be minimized due to ecological and labor protection reasons (i.e. the Autobahn bearing layers should be as thin as possible); on the other hand the deformability of the layer system has to be low enough to meet the stringent German Autobahn limitations in this regard (i.e. the bearing system should be stiff enough to equalize differential settlements due to the heterogeneous waste below).

The owner asked for verification by analytical procedures being common in European Codes beside any possible numerical analyses.

It was obvious that only high-strength, high tensile stiffness geosynthetic reinforcements could help to solve the problem.

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 to include the influence of different embedment below the bearing reinforced layers. Totally four methods were used, and the most conservative results in terms of reinforcement needed were taken over as decisive.

The final solution includes two geogrid families: knitted geogrids from Aramid (AR) and laid/welded geogrids from high-tenacity Polyester (PET).

Execution of the project started in February 2019 and will be finished in October.

The paper describes the boundary conditions of the project, philosophy, design methods, their modifications, material parameters, results of the different methods and the final solution.