Potsdamer Platz in Berlin is the site of a 70,000 m² development that is creating a new city center, with a myriad of offices, housing, shops, entertainment and recreational facilities. As most of the buildings reach far below the groundwater level, the construction of deep building pits is necessary. Due to underground conditions and environmental protection requirements, sealing injection layers can not be used for the deeper parts of these building pits. The remaining solution is to construct an underwater concrete slab, back anchored by tension piles. These building pits are irregularly shaped, with extremely high water pressure on the concrete slab. In order to increase overall safety, steel fibre concrete has been used to achieve a robust and ductile construction.