The expansion of the U2 and U5 in Vienna is unthinkable without the stable and long-lasting building material concrete. Recycled concrete is also used in the largest climate protection project in the federal capital.
When it comes to sustainable infrastructure construction, concrete plays a key role as a building material. Its stability, pressure resistance and, above all, longevity are important prerequisites for a modern, long-term infrastructure. This is also the case with the current expansion of the Vienna subway lines U2 and U5. In the first construction phase of this major infrastructure project, which is often praised as Vienna’s largest climate protection project, the U2 line will be expanded from Schottentor to Matzleinsdorfer Platz. “Concrete is used in many ways in subway expansion. During tunneling, the rock or subsoil is secured using shotcrete. Prefabricated concrete rings, so-called segments, are used for the tunnel walls,” explains Sebastian Spaun, managing director of the Association of the Austrian Cement Industry and board member of Beton Dialog Austria. “Regardless of how it is used, whether as ready-mix concrete or prefabricated concrete, there is one thing you can always rely on with this building material, even under the toughest conditions: when it comes to longevity and safety, concrete is simply irreplaceable.”
Innovative construction methods
When expanding the Vienna subway network, several construction methods are being used: Where staircases or emergency exits will be built on the surface in the future, the so-called cover construction method will be used. Bored piles or diaphragm walls are made from reinforced concrete, between which the excavation pit is dug. This is closed with a concrete cover and then dug level by level until the necessary depth is reached and the shaft is completed with a 1.8 meter thick reinforced concrete slab.
When building subway tunnels, two construction methods are used: station tubes, passage distributors and cross passages are built using the so-called New Austrian Tunnel Construction Method (NÖT). “With NÖT, the mountains or the subsoil become the supporting component. After the eruption, the cavity deforms until it finds a new state of equilibrium. The cavity is then secured with quickly hardening shotcrete,” explains Prof. Konrad Bergmeister, head of the Institute for Structural Engineering at the University of Natural Resources and Life Sciences (BOKU) in Vienna. “The tunnel boring machine has proven itself for longer sections with a uniform tunnel course: it carries out all the essential work steps, from digging the tunnel to lining the tunnel shell with segments,” says Bergmeister. The “clever” machine even takes care of the removal of the excavated material. This will be transported for the entire new route between Matzleinsdorfer Platz and Augustinplatz via the central shaft at Matzleinsdorfer Platz – saving around 20,000 truck trips through the city and 75 tons of CO2.
Station in the densely built-up Margareten
The future Reinprechtsdorfer Straße U2 station is considered to be the only completely new station on the southern U2 route, as there will be no transfer options to the existing U-Bahn and S-Bahn lines here. The station is located in several low areas between the shaft at Bacherplatz in the north and Siebenbrunnengasse in the south. Here, too, the building material concrete is used in a variety of ways: “When producing shafts using the cover construction method, bored piles made of reinforced concrete and gusseted concrete are used between the bored piles. Waterproof concrete is used as in-situ concrete using formwork to produce the inner shell of the shaft structures. In tunnel construction, we use shotcrete that is up to 35 centimeters thick,” says Michael Zeman, project manager for the construction section U2/19 “Reinprechtsdorfer Straße” at Wiener Linien.
Recycled concrete for the first time in Vienna’s subway construction
As part of the ÖBV and FFG research project “Green Infrastructures”, the use of recycled concrete is being tested for the first time in the U2 expansion. To this end, Wiener Linien is carrying out intensive investigations together with the concrete manufacturer Wopfinger Transportbeton and the Institute for Structural Engineering (IKI) at BOKU. “The aim is to produce part of the inner shell of the future emergency exit on the U2 line atQuellenplatz using recycled concrete and reduced innovative reinforcement. For testing purposes, a test field of around 112 cubic meters with an inner shaft shell made of recycled concrete will be built at a depth of around 25 meters and tested for influences such as frost, water pressure and chemical attacks,” says Prof. Konrad Bergmeister. The result should be an inner shell made of recycled concrete that has the same quality as conventional concrete.
About Beton Dialog Austria
Beton Dialog Austria is the interest group of cement, precast concrete and ready-mixed concrete manufacturers in Austria. The aim of Beton Dialog Austria is to anchor in the public mind the importance of the recyclable building material concrete for environmentally and climate-friendly construction as well as the progress the industry has made so far in reducing CO2. More information