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Alexiew, Dr.-Ing. D.

Bridging a Sink-Hole by High-Strength High-Modulus Geogrids


A section of 'Federal Roadway B 180' at Neckendorf near Eisleben, Germany, is once again in service after being blocked for years. The roadway was destroyed across its entire width in 1987 by a sink-hole. The sink-hole, located along the centerline of the roadway, is 30 meters deep and 8 rneters in diameter. Although the hole has been refilled, the danger of a new subsidence due to deep underground caverns still exists. In order to put the road into operation again, the sinkhole had to be bridged to ensure acceptably low deflection values of the roadbase even under heavy truck loads.

Due to lower costs and 'ductile' deformation behavior, a geogrid­ reinforced gravel cushion was preferred to a concrete bridging plate. A geogrid with very high strength (UTS = 1200 kN/m) and high modulus (40 000 kN/m at 3% elongation) was chosen. The project is the first of its kind using high-modulus geogrids in Germany for road construction. The road has been in use since October 1 993 without any further deformations.

This paper describes the reinforcement concept, design philosophy, dimensioning, materials used and safety measures (control system) installed, and provides details and photographs of the reconstructed roadway.


A deep sink-hole was refilled and bridged by a geogrid-reinforced soil cushion. Briefly described are the design philosophy, soil reinforcement materials, and construction technique used to repair the collapsed roadway. The geogrid design methodology, according to Engish and German guidelines and standards resulted in the need for an extremely high-modulus high-strength uniaxial geogrid having a machine direction UTS of 1200 kN/m and elongation at break of 3 %, A measurement/control system was installed to monitor potential future deflection due to the safety requirements for the Federal Roadway B 180. The geogrid reinforced gravel cushion which was constructed without difficulty was the first structure of its kind in Germany.