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Poland’s largest diameter tunnel completed

The breakthrough on the second tunnel bore on the Slowacki Highway Project marks completion of the tunnelling phase on Poland’s first tunnel boring machine (TBM) driven scheme.

The 1.1km long tunnels form the centre of the 10km Slowacki route, creating a road link between the Baltic city’s airport and the deep water seaport. The parallel tunnels will now be fitted with road works.

The geological conditions while crossing under the Vistula River at depths of between 9 and 35m proved to be challenging. In some places only 6m of soil separated the TBM from the riverbed.

The overall project is being delivered by Spanish construction company Obrascon Huarte Lain OHL, which ordered a 90m long, 13m diameter Mixshield TBM from Herrenknecht for the tunnelling work. Keller Polska was subcontracted for the ground engineering ramp work.

For the production of the underground structure segments, Herrenknecht Formwork Technology supplied four sets of molds with an inner diameter of 11m. In order to keep the work as stable as possible and to protect it against buoyancy, the thickness of the concrete lining segments was designed to provide extra strength. For this reason, 600mm thick tunnel segments weighing 18t were used.

The equipment was designed in such a way that tunnelling could also be carried out on the steep 4% downward and upward gradients at the beginning and in the second half of the tunnel respectively.

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