The expansion of the U2xU5 line crossing will be carried out in two construction stages, whereby the first construction stage includes the extension of the U2 from the Rathaus station to Matzleinsdorfer Platz along with the U5 from Karlsplatz to Frankhplatz. The subsequent second stage of construction, which involves the construction of the U5 stations until Hernals and the U2 stations until Wienerberg, is currently in the planning phase.
Bauer Spezialtiefbau Ges.m.b.H., the Austrian subsidiary of Bauer Spezialtiefbau GmbH, was commissioned by the joint venture U2xU5, comprising the companies Swietelsky AG, Hochtief Infrastructure GmbH and Habau Hoch- und Tiefbaugesellschaft m.b.H., to construct approximately 35,000m of piles with diameters of 620mm, 880mm, 1,180mm and drilling depths of up to 61m for nine shafts and station structures in the middle of the city centre of the Austrian capital (contract sections U2/22 & U5/2). For this purpose, up to five large rotary drilling rigs are being mobilised in the period from April 2021 to fall 2022.
The prevailing geology in the project area is characterised by deposits from the Vienna Basin (Miocene), which are overlaid with backfill, loess loam and water-bearing quaternary gravel. In contrast to the contract sections between the U2 stations Matzleinsdorfer Platz and Neubaugasse, where the line tunnels under construction are generally in Miocene (Wiener Tegel soil) layers, the tunnel axes in the area where Bauer Spezialtiefbau is carrying out work between Rathaus and Schottentor are situated in the water-bearing quaternary layers. Due to these connected free bodies of water in the quartz gravel, in combination with the confined groundwater of the sandy Miocene layers, bored piles embedded into Miocene layers generally have to be constructed under water load.
When it comes to the construction of the bored piles, the subsequent construction tasks and expansion work in most construction sections require compliance with higher tolerance requirements compared to the standard. Requirements include drilling precision with a maximum tilt deviation of one per cent with respect to the drilling depth from the drilling surface and the use of a drilling template that must be constructed precisely at the approach level down to +/- 3cm.
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