Telekom site, Constance

Züblin AG commissioned the Stuttgart branch with various specialist civil engineering tasks in connection with the revitalisation of the Telekom site in Constance: In addition to the micropile foundation for the new balcony on the renovated Telekom tower, the package included foundation piles for the underground car park, large-diameter drilled piles for two crane foundations and a shoring wall with anchoring. The existing shell forms the basis of a modern residential tower. The roughly 11,500m² site of the Constance Telekom tower will be converted into an inner-city quarter with around 250 flats in the residential tower and adjacent new buildings, and three commercial units on the ground floor of the tower. The most prominent feature of the high-rise building is the in-situ concrete balconies on the longer sides, whose parapets reflect the colours of the surrounding park.

Subsoil ranges from hard marl to soft lake clay

The geological conditions in Constance were a particular challenge for the specialist civil engineering work. The 16 large DN880 bored piles for the crane foundations,

for example, had to be set through 40m of marl layers with embedded, water-bearing layers of gravel and sand. The drilling depth made it necessary to divide the reinforcement into pieces.

The balcony loads were transferred into the Constance lake clay stratum, partly via the reinforcement of the existing floors, and partly via 84 micropiles ranging between 23m and 25m in length. The clay’s high water content and correspondingly low load-bearing capacity meant that the team had to proceed extremely carefully. To reach this layer, the piles had to be driven through very hard and abrasive soil. This is why the double-head drilling system with a down-the-hole hammer and crown was chosen for the construction of the micropiles instead of the originally planned Ischebeck drilling system.

A total of 73 DN880 foundation piles were used for the foundation of the underground car park down to a depth of 20m, and 36 DN1180 and DN750 bored piles were constructed for the anchored shoring wall.