Single Shield TBM: Safe through brittle rock.
Single Shield TBMs are the right choice for brittle or soft rock. In shield tunnelling, the tunnel is lined with concrete segments. To tunnel forward, the hydraulic thrust cylinders of the Single Shield TBM push against the last installed lining ring.
Wienerwald and Perschling, Austria
Three Herrenknecht Single Shield TBMs demonstrate the power of mechanized excavation in a country where traditionally the "New Austrian Tunnelling Method" is used for excavating hard rock. Five railway tunnels are being built between the Austrian capital and St. Pölten as part of the expansion of the Westbahn leading from Vienna to Wels: the Perschling tunnels and the two Wienerwald tunnels. A total of 27.8km of marl, sandstone, molasse and other soil types are being excavated. The tunnels are scheduled for opening in 2012.
Islisberg, Switzerland
On the 21st April 2005, after only 54 weeks one-shift operation, we saw the breakthrough of the 4,680m western tube of the Islisberg tunnel. Since mid June 2004, the average weekly advance had been 103m. The best weekly advance was 110m. After resetting and converting the 160m long TBMs weighing 2,000 tons, the team started on the eastern tube at the beginning of July 2005. In July 2007, the jobsite team was able to celebrate the final breakthrough. The Islisberg tunnel, which on completion will be the longest underground section of the western Zurich bypass, will be directing transit traffic to central Switzerland around the city.
Arrowhead, USA
Nobody has ever excavated so close to the site of earthquakes before. The route of the S-233 and S-234 through the South Californian mountains above San Bernardino is only a few hundred meters away from San Andreas Fault. The so-called "Inland Feeder Project" is intended to close the largest gap in the Los Angeles drinking water supply network. In 2002, Herrenknecht was commissioned with building two very special machines for the project. These machines were not just equipped with flexible shields but also had to be able to resist static water pressure of up to 10bars. Excavation is extremely difficult because the face can often only be stabilized by injecting large amounts of colloidal silicone compounds.
