The Grand Prix racing circuit at Nürburg has been made even more attractive by the addition of a new section known as the Mercedes Arena, near the start-finish line. The racing circuit has been extended by approximately 600 m within sight of several spectator stands. Through its new curve combinations and overtaking opportunities the new stretch presents the motorsport spectator with even clearer and more exciting views of the race.

Reinforced fill proves best option for steep slope embankment

Extensive earthworks were required to create the required event viewing areas. In reshaping the site, the top of an existing embankment had to be extended in width by approximately 10 m, with the maximum construction height, of the new fill, being approximately 21 m from top to toe.

An additional design constraint was the inconsistency of the existing ground, this being the deciding factor in the selection of the method of steep reinforced fill slopes.

In the opinion of the design engineers; "A steep embankment made of reinforced fill using Huesker´s geosynthetics proved the best way to meet the requirements of the brief."

All the recyclable excavated material was able to be re-used immediately in building the steep reinforced fill embankment. The embankment had to be positioned and aligned to fit in harmoniously with existing structures, such as an access tunnel, a collecting basin for surface water, and service roads.

Building in winter - Geosynthetics make it possible

The racing season at the Nürburgring does not just involve the F1 Grand Prix and other prestige events; it starts in April with daily test drives for various car manufacturers, driver training, and other popular sports events.

The site manager added: "Finishing the project on time for the start of the season in April was our highest priority and we could not have achieved it using other methods of slope stabilisation.

The reinforced earth design allowed us to work practically without interruption during the six months between November 2001 and April 2002; and that was in the well-known, harsh climatic conditions of the high Eifel region with its snow and temperatures down to -15°C."

Advantages of steep reinforced fill slopes

The reinforced fill embankment design offered many advantages:

Flexible geometry, pleasing appearance of grassed slopes

The structure blends in harmoniously - in contrast to other designs. The geometry and slope of a steep embankment is very flexible and amenable to alteration, whether it is on tight radii or straight lines. The appearance of the structure in the surrounding landscape is clearly enhanced by the green facing, using an erosion control mat and appropriate vegetation via hydro-seeding.

Stability during construction and quality assurance, guarantees high performance

During construction, steep reinforced fill slopes are already very stable and can support considerable loads, which is exactly what the contractor found during the building phase. Even heavy construction machinery such as tracked plant and lorries were able to approach quite close to the edge of the slope without any problem. Site plant achieved very high outputs. Up to 1000 tonnes of material per day were able to be placed.

The steep reinforced fill embankment was constructed using recycled slag in 0.45 m thick layers. The compaction of each individual layer was monitored and recorded by the measurement computer in the roller driver's cab. Quality assurance was provided by third party monitoring carried out by an independent soils laboratory.

Each layer was reinforced with the appropriate type of Fortrac® geogrid according to the design. Huesker, the manufacturer of the geogrid, has the ability to match the raw materials for Fortrac® to suit particular site requirements. Fortrac® is provided with a polymer coating to protect it from installation damage and the chemicals attack.

The geogrid restrains the steel face reinforcement mesh, covered by an erosion control mat, by a 'wrap back' into the embankment fill.

Holes and other modifications in top geogrid layers

The posts for the safety fence, at the top of the slope, were able to be driven through the top layer of reinforcement.

By anticipating this reduced strength of Fortrac® geogrid at the design stage, the resulting isolated holes in the geogrid were not a problem.

In areas where ducts and other services plant would cut through the top layer, they were laid in trenches along the edge so that the necessary anchor lengths of the geogrids into the embankment were preserved.

Positional stability and settlement

Steep reinforced fill embankments have many advantages. The Nürburgring was constructed during the quiet winter months. Fortrac® geogrid was used as slope reinforcement.

Fig.1: Steep reinforced fill embankments have many advantages. The Nürburgring was constructed during the quiet winter months. Fortrac® geogrid was used as slope reinforcement.

Fig.2: The reinforced steep slope was constructed using recycled slag in 0.45 m thick layers. The compaction of each individual layer was monitored and recorded by the measurement computer in the roller driver's cab. In addition, third party monitoring was carried out by an independent soils laboratory.