Amstetten, December 2009

Doka press release

Emergency ventilation cavern, Wienerwald Tunnel

Rentable comprehensive formwork solution for geometrically challenging tunnel cavern

The widening of Austria’s main “Westbahn” east-west railway to four-track width between Vienna and St. Pölten is one of the biggest infrastructure building projects currently underway in the country. The centrepiece of the project is a new twin-tube tunnel running for more than 13 km beneath the hilly “Wienerwald” (Vienna Woods) district between Hadersdorf and Klein Staasdorf. On the 11 km long Western Section, two tunnel boring machines were in service. The much shorter (2.3 km) single-tube Eastern Section was constructed conventionally by mechanical excavation and blasting, using the New Austrian Tunnelling Method. Unlike in the Western Section, where the tunnel tubes are being automatically lined with segments, the drill-and-blast method used in the Eastern Section requires the inner shell of the tunnel to be constructed in cast-in-place concrete. An over 10 m high and 35m long emergency ventilation cavern set at 90° to the tunnel constitutes the transition zone between the two contract sections. With its many geometrically challenging intersections, transition zones and headings, the emergency ventilation cavern is one of the most difficult casting sections of the Wienerwald Tunnel from the formwork-engineering point of view. To construct the reinforced-concrete inner shell in and around the cavern, the Works Management of the “Arge Wienerwaldtunnel” JV (consisting of Porr Tunnelbau GmbH, Porr Technobau und Umwelt AG, Bilfinger Berger Baugesellschaft m.b.H, Swietelsky Baugesellschaft m.b.H., Jäger Bau GmbH, Hochtief Construction AG and Züblin Tunnelbau) opted for a comprehensive formwork solution from Doka. Alongside the technically convincing formwork concept, the key factors behind this decision were the above-averagely high proportion of rentable components (over 90 percent), and the high degree of pre-assembly of the formwork equipment.

Shortly before the emergency ventilation cavern, the single-tube Eastern Section broadens to become a twin-tube tunnel. The cavern itself is intended to rapidly ventilate the Wienerwald Tunnel in the event of a fire. Following shotcrete stabilisation of the excavated cross-section, the cavern is being lined with an approx. 50 cm thick reinforced-concrete shell. In the first, 6 m high casting step, the site crew of the Wienerwald Tunnel JV are forming the up to 10 m high end-walls using a combination of Doka supporting construction frames and rentable standard panels from the rugged Framax Xlife framed formwork system. Above this, the high-load Doka dam formwork D 15K, also fitted with Framax Xlife panels, is in use on the second, 4 m high casting step. To facilitate concrete placement, the formwork panels are equipped with filler necks. Both these systems are fully rentable, are built from pre-assembled system components, and come with extensive safety features such as generously sized working platforms and integrated vertical access facilities. “With this formwork solution, we were able to pour the end walls in a safe, fast and cost-effective way”, explains site engineer Robert Uschan.

Dimensionally accurate formwork for complex intersections

The 35 m long sidewalls were formed with large-area elements of Doka Top 50 formwork on 6 m high Doka supporting construction frames Universal F. For the geometrically difficult intersections with the tunnel tubes, the Doka project technicians planned intersection elements which were specially tailored to the complex geometry of the structure. Based on Large-area formwork Top 50, these elements were prefabricated with complete dimensional accuracy by the Doka “Ready-to-Use” Service and supplied to the site ready-assembled. “By using these pre-assembled intersection elements, we have saved a huge amount of time and achieved a first-rate result”, says site engineer Robert Uschan, neatly summing up the benefits of working with the Doka planning service and the Doka “Ready-to-Use” service.

A Doka tunnel-formwork traveller, consisting of 3 sections in the longitudinal, is in action for pouring the cavern vault. The traveller is built from rentable standard components of the Heavy-duty supporting system SL-1 and fitted with Large-area formwork Top 50. Thanks to the system’s high proportion of rentable system components, and its pre-assembled parallel truss segments, it can be finally assembled very quickly on the site, ensuring fast and efficient construction progress. In addition, experienced Doka field service technicians were on hand to help the site crew assemble the tunnel formwork traveller correctly. Using custom-built intersection elements, it was also possible to form and pour the transition zone between the vault, the sidewalls and the tunnel tubes quickly and accurately. As well as the formwork solution for the emergency ventilation cavern, Doka also kept this major underground site supplied with just-in-time deliveries of formwork for transformer recesses, escape galleries and jet-vent tunnels. Detailed planning of the formwork operations, including verifiable statical calculations, formwork pre-assembly and just-in-time site delivery, round off the extensive spectrum of Doka products and services provided to this challenging construction project.

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Doka_1.jpg: This cavern vault is being cost-effectively and time-savingly formed using a modularly designed Doka tunnel formwork traveller.

Doka_2.jpg: The exactly fitting, pre-assembled formwork elements make it possible for the geometrical intersections to be formed and poured with great precision.