A MASSIVE cofferdam built to allow construction of part of the new German parliament complex in Berlin has been left as a permanent feature to protect the historic Reichstag building.
Steel sheet piling from British Steel has been used to form part of the 30m deep cofferdam surrounding the foundations of the Aisenblock, one of three new buildings - along with the Reichstag - that will make up the German government's new home.
The Aisenblock is being built alongside the Reichstag. The main problem on this and other major construction projects currently in progress in the capital (GE September 1997) is the city's difficult water-bearing ground, consisting mainly of gravel and sand.
Disturbing the high water table, commonly at 1.5m below ground level, had the potential to cause damage to wooden piles supporting the Reichstag, so a watertight barrier was needed to isolate the building and allow construction of the new foundations without affecting groundwater levels.
First, a 30m deep slurry wall made a watertight vertical barrier, with a watertight base slab cast by pressure grouting the granular material at the foot of the slurry wall. A wall of LX25 steel sheet piles was then inserted in the top 15m of the wall and tied back with raked ground anchors, forming a retaining structure for the temporary excavation.
And to provide permanent protection, the wall was left in place and the cofferdam flooded after the foundations were complete.