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Due to expected capacity requirements for public transport during the 2006 Football World Cup, it was decided to enlarge the metro station Marienplatz, situated right beneath Munich city hall. The project concept finally approved provides for two extra tubes running in parallel to the existing ones. By connecting the new and old tubes with 11 cross cuts each approximately 3.10m wide, an intended doubling of the platform passenger capacity is achieved.
The close vicinity of the new tunnel tubes to existing buildings – in particular the historic city hall ‘Neues Rathaus’ that was erected from 1867 to 1909 – puts a high demand on control and limitation of the soil movements to be expected during the construction process. While the original bid invitation proposed a lowering of the groundwater level, the solution finally chosen uses an innovative brine freezing technique, a specific proposal made by the executing consortium.
As the analysis covers numerous non-linear construction stages involving parametric studies, it was essential to have a fast solution technique. On the other hand, simulation of the cross cutting process is a complex non-linear three-dimensional problem. Aiming at the best compromise between efficiency and required accuracy, a novel concept was adopted. It started with a classical two-dimensional finite element analysis of representative cross-sections using standard and approved techniques but was extended to account for the three-dimensional stress redistribution effects occurring during tunnel excavation. A special combined mesh generation and mapping technique is applied to create a three-dimensional model that inherits the load history induced by the tunnelling process and thus allows for simulation of the cross cut installation process.
This combined approach enables the complex analysis task to be performed within a reasonable timeframe.
SOFiSTiK AG, Oberschleissheim, Germany
Schmitt Stumpf Frühauf & Partner Ingenieurgesellschaft mbH, Munich, Germany