|Company||PORR Tunnelbau GmbH in a consortium|
|Principal||ÖBB Infrastruktur Bau AG|
|Location||Chorherrn - Austria|
|Type||Tunneling, Rail construction|
|Runtime||07.2004 - 01.2010|
22 kilometres of challenges
The Wienerwald Tunnel is part of the four-track expansion of the western railway (Westbahn) between Vienna and St. Pölten. The stretch is built to handle speeds of up to 250km/h.
9,552 tubbing rings, each consisting of six segments, were installed on the approximate 22km of tunnel tubes. For this, around 57,000 prefab concrete parts had to be produced every day, corresponding to 120 elements per day. To be able to supply this enormous amount of material, a tubbing production facility was set up directly on site – at the west portal of the tunnel.
However, this was far from the only challenge that the consortium’s team had to master on this project. The project plan foresaw tunnelling output of 750m a month. The circular profile and very re-entrant base section added enormous pressure, which significantly increased the load on the concrete. Conventional approaches such as ballasting or support in the roof could not be used. The consortium developed a rapidly setting concrete mix specifically for the base section; this mix could absorb the loads from the overlying fresh concrete during the pouring process without transferring unfavourable buoyant forces on the shuttering. What’s more, the concrete had to remain workable for longer periods due to the long transport routes to the installation site. The construction method selected enabled the tunnel’s 21.5km inner lining to be completed in just 16 months.
Another difficulty came from the fact that the east drive had to be built from an existing railway tunnel constructed with diaphragm walls without restricting the rail service on the existing tracks.
Excavated material was transported using a rail loading system at the east portal with the help of a conveyor belt system to the Taglesberg landfill and for earthworks in Tullnerfeld. Once the works were completed, the construction site was recultivated and greenery was planted.
Last but not least, the construction site was in an inner-urban location, meaning that comprehensive measures to prevent noise and to protect the environment had to be employed.
The project can be roughly divided into four sections:
- Single-tube east drive, cyclical driving, length: 2,370m, cross section: 87 to 245m², including side wall galleries (75m), pipe shield (320m) and ventilation chamber with emergency ventilation shaft (diameter: 4.50m, depth: 200m)
- Double-tube west drive, continuous driving with two open shield tunnel boring machines (diameter 10.68m) in loose rock (Flysch, Molasse), length two times 10,750m, with two-shell lining (tubbing and inner lining relieved of pressurised water)
- Mucking gallery (sloped gallery with a gradient of 32%, length: approx. 500m) and Taglesberg landfill
- West earthworks approx. 10,400m