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Scientific Reviewed Papers
Alexiew, Dr.-Ing. D. | Elsing, Dipl.-Ing. A. | Ast, W.

FEM-Analysis and dimensioning of a sinkhole overbridging system for high-speed trains at Gröbers in Germany

Abstract

Roads and railroads crossing sinkhole areas are a problern of increasing importance. The range of possible solutions is dominated by geosynthetic reinforced systems. Although some analytical procedures are available for design, for an increasing num­ ber of cases they are not precise enough or not applicable. Numerical procedures provide some help. Based on the project Gröbers on the new high-speed rail link Leipzig-Halle such a case is discussed. The bearing system bridging sinkholes consists of a cement­ stabilized soil block with basal geogrid reinforcement. The main problems of design were to check both Serviceability and stability of the system for a pre-failure and a partial post-failure state as weiL A commercially available FEM-eode could not solve all problems, e. g. the post-failure analyses. Thus, analytical procedures were developed and applied. An overview of all checks and corresponding FEM and analytical calculations is shortly presented. The final project specifications were based on the design described. The bearing system is already built.

Conclusion

A complex geotechnical structure for overbridging sinkholes in­ cluding cement-stabilized soil and geogrids at its base was designed for the German Railroads at Gröbers. The bearing system consists of a stabilized soil block and extremely high-strength geogrids.

A clear scheme of checks was established which is conform to the actual German and European codes especially regarding the analysis of the different Iimit states: the ultimate Iimit state and the Serviceability Iimit state. All checks and design calcula­ tions were performed taking into account such factors as differ­ ent positions of train Ioads and sinkhole, time-depending behav­ ior of geosynthetic reinforeerneut (and consequently of the entire system) etc. a commercially available FEM-eode was successfully used for many checks required. It was an unavoidable and very useful tool, but FEM-calculations alone were found to be insufficient for this complex problem.

To ensure a sound and really safe design especially for post­faHure analysis new analytical procedures or generally new con­ cepts were developed and used: analysis of the critical geogrid tension and deformation after a partial failure of the cemented soil block and analysis of the remaining block after the afore­ mentioned partial failure using an 'arch bridge with tension member'-analogy.

For the Serviceability Iimit state and for the definition of the

required design stress-strain (deformation) parameters of soil block and geogrids the FEM-analyses were decisive.

The required short-term and long-term design strength ofthe

geogrid reinforeerneut was finally evaluated by the post-failure procedure, and the required design soil block strength - by the 'bridge analogy'.

All design calculations and results were approved by the German Railroad Supervising Authority. The resulting require­ ments on soil and reinforcement became a part of the final project specifications. Further information regarding the project can be found in (Ast & Hubal2001, Leitner et al. 2002).

The construction of the bearing structure discussed herein started in 2001 and was nearly completed until May 2002. Traffic will start in 2002.