Near Minden, a town in northwestern Germany, the country´s longest waterway – the Midland Canal – crosses the river Weser on two viaducts. Part of this historic landmark is a road and rail subway tunnel that crosses the canal 11 m below. Built 90 years ago, the tunnel was a safety hazard and had to be demolished and rebuilt.
Coffer Dams, Sheet Pilings, Demolition
At first, a coffer dam was erected on either side of the tunnel passage so
that the construction site could be drained. For safety reasons, the coffer dams were double-sided and weighed 1.400 tons. Then the tunnel, protected
from the canal water by the coffer dams, was uncovered and demolished. Following this, canal work was done and the foundation for the new tunnel poured.
Forming the Side and Cross Walls
The new tunnel was built on the footprint of the old tunnel. While the old passage consisted of two tunnels that were arched at the top, the new passage is a rectangular shell over both the road and rail tracks, 15 m wide, 39 m long. 2.200 m3 of reinforced concrete were poured to build it. Boards with tongues and grooves were attached to the formwork to give the concrete surface a board structure.
The 27 m tunnel has a 1.10 m thick ceiling slab. Special alignment rails were used to integrate a cove at a wall height of 4.10 m and at an angle of 146°, see the top right photo. Later, when forming the slab edge, these alignment rails were used a 2nd time.
At the end of the tunnel housing, 11 m high walls were formed with a 30 cm thick slab to support the maintenance tunnel. MEVA wall formwork Mammut was chosen because of its load capacity of 100 k/N/m².
MEP Shores and MevaFlex for the Slab
MEP shores were ideal to carry the heavy load of the shell´s ceiling slab. They are easy to assemble, even to a height of 5.60 m. By using height extensions, the shores were extended to a height of 11 m and used to support the maintenance paths. This way, the same system could be used for different applications. Sheet piles were used as a foundation and later piledriven to serve as a bulkhead.
MEVA StarTec for the Tub Walls
The Midland Canal runs at an angle of 90° to the tunnel. At its back end and parallel to the canal, tub walls were formed with MEVA´s StarTec wall formwork. The tub walls have a trough at the top which will later be filled with soil to grow flora. They start at the top of the tunnel and extend 4 m to the level of the canal (50.30 m above sea level plus 1 m freeboard).
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