Excavation pits & pile foundations

Excavation and pile foundation for new ILB headquarters in Potsdam

The new headquarters of Investitionsbank des Landes Brandenburg
(ILB) – the central investment and development bank of the German Federal State of Brandenburg – is located in the centre of Potsdam, behind the main station. In November 2014, a consortium comprising FRANKI, KELLER and PRB Spezialtiefbau was contracted to handle
the foundation engineering works.
The excavation pit needed for the new bank headquarters was 10 m deep, with an area of 2,850 m2. The subsoil conditions here are ex-
tremely fractured due to former channels of the nearby rivers, the Havel and the Nuthe. Moreover, the loadbearing sands exhibit varying packing densities. Given the absence of any impervious strata invulnerable to uplift, the site team adopted a cut-off wall solution in conjunction with a low-level jet-grouted waterproof base. Sheet piles were inserted in the cut-off wall and secured by temporary anchors.

Unexploded ordnance and 3,500 kg of explosives
Due to the existing river deposits, full-displacement piles were used for only part of the foundations. To provide adequate protection against building uplift, FRANKI installed partial-displacement auger piles at loca-
tions where the sands exhibited high packing densities. Following the detection of strong ferromagnetic anomalies within the fill on the site,
the site team decided to dispense with exploratory boreholes to check
for explosive ordnance. It was therefore necessary to dispose of the
entire fill under the supervision of the explosive ordnance disposal
(EOD) service. The associated earthworks led to the discovery of two
unexploded 250 kg bombs that had to be defused on site. Also recover-
ed were a further 3,500 kg of explosives, which it was possible to
defuse elsewhere.

Reinstatement of groundwater flows
Following completion of the structural works inside the trough-enclosed excavation, two-thirds of the sheet piling was extracted from the cut-off wall. The formation of three "windows" in the cut-off wall was then need-
ed to ensure the unobstructed flow of groundwater. For this purpose, large-diameter boreholes were sunk to a depth of 21 m along the line of the cut-off wall and filled with gravel. The finished pit was handed over
to the client in mid-July.

Contract works:
230 displacement auger piles, d = 51 cm, Nk ≤ 2.000 kN, L ≤ 15,0 m
430 Atlas piles, ds/db = 41/51 cm, Nk ≤ 2.000 kN, L ≤ 15,0 m
4.500 m² cut-off wall, d = 60 cm with inserted sheet piling
2.850 m² jet-grouted waterproof base
125 temporary strand anchors, Zk ≤ 500 kN, L ≤ 15,0 m
70.000 m³ earthworks

Would you like to know more?
Project manager: Mario Prütz
Tel.: 030 4057165-15

ILB-Zentrale in PotsdamILB-Zentrale in PotsdamILB-Zentrale in Potsdam

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