Work is advancing on the extension of the southern U1 subway line in Vienna. The new section is 4.6 km long, includes five stations and ends in Oberlaa. Beginning in 2017, the U1 subway line with a total length of 19.2 km will be Vienna's longest.
The new section runs primarily underground – only the southernmost section will be above ground. Because the two parallel, single-track tunnel tubes are partly located at a depth of nearly 20 m, tunnel excavation posed challenges to the participating companies. The soil in this area is very cohesive, but also contains water-bearing strata that had to be drained. For this purpose, a large number of wells and water gages were built that were necessary for relieving the waterbearing layers.
New Austrian Tunnelling Method
A large part of the subway station and tunnel sections as well as the crossways for this project were advanced using the New Austrian Tunnelling Method. Most of the tunnel sections and crossways were advanced in a full-circle tunnel heading with an advancing crown being realized shortly before the invert. Ground support products that were used included spiles and forepoling boards in addition to reinforced shotcrete.
For tunnelling pre-support, DSI Austria supplied DYWIDAG GRP Anchors and GRP Mats, lagging sheets and the DYWI® Drill Hollow Bar System with accessories. Furthermore, DSI supplied Ø 51 x 3.2 mm vacuum lances with accessories. Lattice girders were used for immediate support in the open span area. In addition, the pipe umbrella system with nipple connections was used for pre-support. These products provide optimum support for local unstable areas in the work area and prevent stress relaxation during installation.