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Excavation pit and pile foundation for new ILB headquarters in Potsdam

Photo: The square excavation pit with numerous construction machines is located in the middle of a large earthy area. The piles are just constructed.
Facts and Figures
Company ARGE Franki, Keller, PRB
PrincipalInvestitionsbank des Landes Brandenburg ILB
LocationPotsdam - Germany
Type Specialist civil engineering
Contract duration07.2018 - in progress
Runtime10.2014 - 06.2015

Pile manufacture on dangerous terrain.

The Investment Bank of the State of Brandenburg (ILB) has built a new headquarters behind the main station in downtown Potsdam. In November 2014, the joint venture of FRANKI, KELLER and PRB Spezialtiefbau was awarded the contract for the foundation and special civil engineering work.

The new bank building required a 2,850 m2 construction pit ten metres deep. The former channels of the adjacent rivers Havel and Nuthe make the building ground extremely desolate. The load-bearing sands are also stored in different densities. Since there are no sealing soil layers in the buoyancy-safe position, the site team secured the excavation pit with a sealing wall and a low-lying HDI sealing base. It placed sheet piling in the sealing wall, which was secured with temporary anchors.

Because of the old river deposits, the foundation was only partially constructed with full displacement piles. In order to ensure the building's buoyancy safety, FRANKI used partial displacement bored piles where the sands have high storage densities. On the construction site, strong ferromagnetic anomalies were found within the fillings, which prevented the release of explosive ordnance by means of borehole sounding.

It was therefore necessary to dispose of the entire backfill under technical supervision. During this earthworks two unexploded bombs, each weighing 250 kg, were discovered which still had to be defused on site. In addition, a further 3,500 kg of explosives had to be recovered, which, however, could be defused elsewhere.

After completion of the shell within the trough construction pit, two thirds of the sheet piling had to be removed from the cut-off wall. Three windows in the cut-off wall allow an undisturbed flow of groundwater. For this purpose, large boreholes were drilled to a depth of 21 metres in the retaining wall and filled up again with gravel.