Fortrac® geogrids allow road construction in
impassable terrain near Trieben / Austria

The situation:
The B114 Hohentauer road was built in the 1960s and passes close to the township of Trieben in Styria, Austria. Over the course of a year, the heavily trafficked link between Trieben and Sunk developed serious defects that were beyond repair.
The regional roads management authority looked around for a new solution, which, in view of the geological conditions of its location, would have to overcome some real challenges.
The solution:
After extensive investigations, the Client – the Austrian Federal State of Styria – decided in favour of a new alignment on the opposite side of the valley, more or less parallel to the course of the old road. However, the terrain was highly impassable, with extremely steep hillsides.
Different options for the route were investigated and feasibility reports produced. All the public and private bodies involved with the planning of the new road opted for constructing a large number of sections of the new route on geosynthetic reinforced earth (GRE). The necessarily steep batter slopes on both sides of the road were built up in successive layers of fill, each 600 mm thick and incorporating Fortrac® geogrids, using the "wrapped back" technique to prevent these sections of road from slipping off the hillside. The GRE embankments were up to 28 metres high, which placed special engineering requirements on the geogrid. The geogrid has to be flexible in order to be successfully wrapped back into the next layer of fill. Other important product properties that the selected geogrid has to deliver are appropriate load-extension behaviour and durability. The geotechnical experts and engineers working on the project considered the highly complex requirements and selected Fortrac® geogrid manufactured by HUESKER as the most suitable product. Most of the GRE sections were based on a sprayed concrete frictional foundation. As well as wrapping back the geogrid at the front face, the wrapped-back detail was repeated at the rear face for the lower layers. The flexible HUESKER geogrid offered a unique feature for this particular application that could not be matched by inflexible geogrids. The mesh size of the grid was selected to suit the fill material in accordance with recommendations for geosynthetic reinforcement published by Deutsche Gesellschaft für Geotechnik e.V. – in this case 70 x 70 mm.
The experience and bold approach to innovation of the project participants paid dividends. The use of the selected HUESKER product made it possible to successfully complete the technically challenging new route for the B114.
Project/Location.: B114 near Trieben-Sunk/Austria
Client: Federal State of Styria, Department, 18B Highway Infrastructure Construction
Design: Dipl.-Ing. Johann Birner, and Dipl.-Ing. Dr. techn. Karl Lackner,
8042 Graz
Contractor: ALPINE GmbH, Salzburg
Construction period: 2006 - 2009
Product: Fortrac® R 55/30-70T; R 80/30-70T; R 110/30-70T; R 150/30-70T; HaTe® 23.142/GR