Fortrac® aramid geogrid protects
A143 motorway western relief road at
Halle (Germany) against sinkholes

Background:
Part of the German government’s post-reunification transportation infrastructure renewal project “Verkehrsprojekte Deutsche Einheit”, VDE Road Project No. 13 comprises the A38 motorway connection Göttingen-Leipzig and includes the A143 western relief road at Halle.
The scheme involves the construction of interchanges on the A7 at Göttingen and the A14 at Leipzig as well as the western relief road around Halle between the A38 and A14 motorways. As it approaches the residential suburb of Halle Neustadt, the route crosses an area of former brown coal workings prone to the formation of sinkholes.
Solution:
The most economic solution was chosen from the range of different options for ensuring the safety of the road. The Fortrac® geogrid type R 1200/100-10 AM used for this project was made-to-measure in accordance with the placing drawings. When a sinkhole forms, the Fortrac® bridges the resulting void and ensures the safety of the traffic above. The system for bridging sinkholes was designed assuming a hole diameter of 4.00 m. The project documentation called for dynamic compaction of the ground prior to installation.
A continuous quality assurance chain involving in-house testing of the yarn and geogrid carried out by the accredited HUESKER laboratory was backed up with third party quality monitoring to DIN 18 200 and compliance testing by the client, DEGES, Berlin. Only after this was the material approved for installation.
The Fortrac® geogrid was placed in one layer longitudinally. The transfer of force was ensured by overlapping the geogrid longitudinally and transversely by the specified amounts. In order to mobilise the load capacity of the geogrid as quickly as possible in the event of a sinkhole forming, it was given a certain amount of pre stress during installation.
To do this, HUESKER has designed a special placing beam, which applies a known pre stress related to the setting of its unrolling resistance.
Fill was then placed over each length of geogrid, working forward progressively to fix the tensioned geogrid in position. This was followed by compaction of the gravel bedding layer. Thus 2.6 km of the A143 road in the Teutschenthal valley were protected.
The all-purpose road L164 crosses the A143 motorway here. A 280 metre length of this road was also protected by Fortrac® geogrid reinforcement against sinkhole formation in this area.
Project/location: BAB A 143
Client: DEGES, Berlin
Planning/design and site supervision: Ing.-Büro WBI, Aachen
Placing drawings: DAS BAUGRUNDINSTITUT Dipl.-Ing. Knierim, Leipzig
Contractor: Walter-Heilit, Verkehrswegebau GmbH, ZNL, Magdeburg
Constructed: 2003/2004
Product: Fortrac® geogrid, type R 1200/100-10 AM