BAUER SPEZIALTIEFBAU has used its doublehead rotary drilling system to form the secant piled retaining walls for a future high-speed rail tunnel link to the new Terminal 2 at Munich Airport in southern Germany.
Similar to the cased flight auger pile system, it features two independent rotary heads, one to drive the continuous flight auger and the other - operating in an opposite direction - to screw in the casing.
This allows greater control and accuracy when forming secant walls. The rotary heads can also be hydraulically linked and rotated together.
At Munich, the system has been fitted to one of the firm's BG42 heavy duty rigs, which the firm claims is the largest of its type in the world.The rig is installing 8,900m 2of 1180mm diameter piles for the tunnel, which will be built by cut and cover.
The high-speed link is only part of the huge amount of geotechnical work under way as part of the airport expansion, which involves 340m extensions to a baggage and supply tunnel and a twin-track railway tunnel to the new terminal as well as a new 540m long passenger transport system tunnel.
Terminal 2 is on the eastern side of the existing passenger handling facilities and is due to open in 2003. The development is a result of a continuous increase in air traffic since the airport opened in 1992, exceeding predictions and using up all spare capacity.
This year, passenger traffic will reach twice the original estimate. By 2010, the airport will be able to handle 40 million passengers a year.
The project is being carried out jointly by the Munich airport authority, Flughafen Munchen, and German airline Deutsche Lufthansa.As well as planning and building the new terminal, the joint venture will also operate it, with Flughafen Munchen contributing 60% of project costs and Lufthansa 40%. The client for construction is the Munich Airport Construction Company.
Work comprises construction of the passenger terminal building, a central apron area and the cut and cover tunnels, which are being built by the Munich Airport Tunnel Structures joint venture (contractor Walter Bau and Bauer Spezialtiefbau).
Geotechnical and foundation work, worth DM86M (£27.5M), has to be carried out between January and December this year.
Because of the tight schedule, up to 15 pieces of heavy duty construction equipment are working in close proximity at any one time.
These are not only installing the secant piled walls, but 33,000m2 of sheet piling, 6,800m 2of 800mm thick diaphragm walling, 1,300m of 880mm diameter bored piles and 830m of 1180mm diameter bored piles (using the double head rotary drilling equipment).
About 8,000m of GEWI piles are also being placed to resist uplift, along with 550 anchors and 150 tie rods.
Mixed in place walls, formed using a triple auger rig, act as cut-offs and structural elements. The base slabs to the excavation are formed using soft gel grout and jet grouting and ground treatment is used to keep the excavations dry.