Excavation pits & pile foundations

Basement excavation for Helmholtz-Zentrum Berlin

A new energy recovery linear accelerator (ERL) is being built at the
materials and energy research institute Helmholtz-Zentrum Berlin für
Materialien und Energie (HZB). Following a complex design process
and comprehensive enabling works, construction of the new bERLinPro
subterranean accelerator hall has started at the Adlershof site on Ernst-
Ruska-Ufer in south-east Berlin. The accelerator hall forms the core
of the compact facility.

Yet, the pioneering accelerator technology is not the only challenge, with
special requirements also placed on the construction works: apart from
the necessary provision for radiation protection, which has involved
housing the accelerator in an underground building, a solution was also
needed to accommodate the high water table at the location.

Subterranean hall on site with high water table
Working with consortium partner Keller Grundbau, FRANKI Grundbau
thus opted for a trough structure, comprising continuous retaining walls
and ground slab, to enclose the basement excavation for the accelerator
hall. During the construction phase, any infiltrating water is pumped away from the building. Trough structures offer a particularly reliable and eco-friendly solution in difficult ground conditions in that they protect the soil and neighbouring buildings against adverse effects.

In the first stage of construction, FRANKI is building a 14 m deep, reinforced, two-phase diaphragm wall, anchored back in deeper parts of the later pit for greater stability. The anchors are being installed by VIT GmbH (a member of the FRANKI Group). Consortium partner Keller Grundbau will incorporate a jet-grouted waterproof barrier at the base of the excavation.
The water table will then be lowered to the level needed for construction. Only then will the excavation works commence, with overlapping concrete lenses placed to form the ground
slab of the pit.

14 m deep, trough-enclosed excavation with two-phase diaphragm wall
The subsoil comprises the sands typically of Berlin sites plus a thin, discontinuous marl layer overlying isolated boulders. The water table is at a depth of around 2.5 m.

The works are progressing apace, with handover to the structural contractor scheduled for late summer 2015. Only then will construction of the accelerator hall commence. To protect against radiation, the hall will be subsequently covered by an approx. 3 m high mound.

Would you like to know more?
Project manager: Jochen Rohde
Tel.: +49 162-200 2457

2.400 m² diaphragm wall,
d = 60 cm, L ≤ 14,0 m
1m thick jet-grouted base,
19 temporary strand anchors,
Zk ≤ 570 kN, L ≤ 24,5 m
Approx. 10.000 m³ spoil plus proper disposal

Diaphragm wall excavator with grab

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