The double-tube City-Tunnel Leipzig - one of Europe's largest infrastructure projects - connects the dead-end stations Leipzig Hauptbahnhof (central station) and Leipzig Bayerischer Bahnhof. The connection of the local traffic and the long-distance traffic will benefit most from the closing of the gap.
All of the tunnelling took place below the groundwater table in heterogeneous glacial ground. The highest precision and safety was required due to the project's challenging inner-city location. The Herrenknecht Mixshield S-326 named "Leonie" was used. It was equipped with the SSP system (Sonic Softground Probing) which helped to detect boulders and other obstacles well in advance and to take corrective measures.
To ensure safe progress in boring the link tunnel under Leipzig Central Station, it was first of all necessary to protect the enclosed excavation pit against potential settlements by installing an icing shield (pipe arch). To this end, a Herrenknecht AVND2000AB was driving two tunnels with a length of 100 and 150 meters. Several small icing pipes radiate from these two preliminary tunnels into the ground. Nitrogen is injected through the pipes into the surrounding ground, freezing the groundwater. This produces two 35 meter high ice walls, which secure the mechanized tunnelling works of the large-diameter tunnel boring machine.
On October 31, 2008 "Leonie" arrived in the target shaft. After 21 months, five intermediate breakthroughs and a total of 2,489 meters of tunnelling, the tunnelling for the City-Tunnel in Leipzig was successfully completed.
