Use of ground freezing ahead of tunnelling work on the Rastatt tunnel on the Karlsruhe to Basel railway line in Germany is under investigation following a ground collapse last week.
The failure has led to suspension of rail services between Rastatt and Baden Baden after ground movements of over 500mm were detected over a 6 to 8m section of track overlying the tunnel route.
The southern end of the tunnel, which passes below the railway line with cover of just 5m at Niederbühl, is currently being backfilled with 10,500m3 of concrete to enable rail services between Rastatt and Baden Baden to be restored. In total a 150m length of the tunnel will be backfilled using boreholes drilled from the surface and will encase the tunnel boring machine (TBM).
The use of ground freezing on the tunnel to enable TBM excavation of parts of the 4.2km tunnel is now being reviewed by German rail infrastructure company DB Netze. Ground freezing has been used extensively to drive the twin bore tunnel through Quaternary and Tertiary deposits and this is the first instance of major ground movement.
The tunnel forms a key part of a 17km section of high speed railway that will connect Karlsruhe to Basel. Construction of the tunnel started in 2016 and is due to be completed in 2018.