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German tunnel collapse repairs ahead of schedule

German rail infrastructure operator DB Netze has said that repairs to a rail line damaged by a tunnel collapse last month will be completed ahead of schedule.

Rail services between Rastatt and Baden Baden have been suspended since the eastern bore of the Rastatt tunnel on the Karlsruhe to Basel railway line collapsed during construction work.

DB Netze originally expected to restore rail services by 7 October but has now revised that to 2 October.

The tunnel failure, which is believed to have been caused by the failure of the precast segmental lining behind the tunnelling shield, caused subsidence on the rail line between Rastatt and Baden Baden. The tunnel bore and the tunnel boring machine – which was just 5m below track level – was backfilled with concrete immediately after the incident to stabilise the site. “Work has been underway to construct a new 100m long, 10m wide and 1m thick ground slab over the eastern bore to ensure long term stability of the existing rail route. A similar structure has also been built above the western bore to mitigate against future problems.

The 4.2km long tunnel was being excavated by TBM using ground freezing to bore through gravel and sand and is a key part of the new 17km high speed rail line between Karlsruhe to Basel.

“In this difficult situation, every day counts for our freight customers and passengers, so it is helpful that we are able to reopen the line sooner than expected,” said DB infrastructure manager Ronald Pofalla. According to Pofalla, the earlier opening date was made possible following an acceleration of the construction programme. 

No details have yet been given on the cause of the collapse, however, industry specialists have suggested that investigations should look at the annular fill used to maintain the integrity of the precast concrete segmental lining. Some have also questioned the use of ground freezing with just 5m of cover over box jacking techniques.

DB Netze has not yet commented on the recovery process for the project or how the collapse will affect the programme on the overall Karlsruhe to Basel scheme. Tunnelling work was originally scheduled to be completed next year.


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