Constance
Telekom site
Konstanz, Germany / 02.2022 - 09.2022
A new urban quarter comprising around 250 flats, complementary new buildings and commercial space is being developed on the former Telekom site in Konstanz. At the heart of the project is the thoroughly refurbished Telekom high-rise, the existing structural shell of which is being retained and further developed for future use. To carry out the construction work, Züblin AG commissioned PORR special civil engineering to provide a comprehensive package of services comprising pile foundations, shoring and anchoring works, as well as specialist foundations for both existing and new buildings.
Facts & Figures
Company
PORR Spezialtiefbau GmbH
Type
Foundations
Runtime
02.2022 - 09.2022
Special civil engineering works for the regeneration of an inner-city quarter
Special civil engineering for existing buildings and new-build projects
The requirements for the special civil engineering work were varied. For the new balcony structure of the residential tower, micro piles were installed to transfer the loads from the cantilevered in-situ concrete balconies into the subsoil. In addition, the project comprised foundation piles for the underground car park, large-diameter bored piles for two crane foundations, as well as the construction of a back-anchored retaining wall. The diverse construction tasks required coordinated foundation and shoring solutions for both existing and new structures within a densely built-up inner-city environment.
Subsoil comprising marl and Konstanz lake clay
The geological conditions on the construction site posed particular challenges for the works. Whilst hard marl layers interbedded with water-bearing gravel and sand layers were encountered at greater depths, the so-called Konstanz lake clay had to be reached for the micro-pile foundations. For the two crane foundations, 16 large-diameter bored piles (DN 880) were installed. The piles penetrated marl layers up to 40 m thick. Due to the great drilling depths, the reinforcement had to be installed in sections.
84 micro piles for the high-rise’s balcony structure
The load-bearing capacity of the new balcony structures is provided partly by the building’s existing load-bearing structure and partly by a total of 84 micro piles. These range in length from 23 to 25 metres and are anchored in the Konstanz lake clay. The high water content and the comparatively low bearing capacity of this soil layer required the work to be carried out with great care. At the same time, hard and abrasive soil layers had to be drilled through before reaching the load-bearing foundation level. Consequently, a double-head drilling system with a down-the-hole hammer and drill bit was used instead of the drilling method originally planned.
Pile foundations for the underground car park and retaining wall
A total of 73 DN 880 foundation piles were installed for the deep foundations of the new underground car park. In addition, a back-anchored retaining wall was constructed comprising a total of 36 bored piles with diameters of DN 1180 and DN 750. The retaining structure secured the construction pit whilst further work was carried out and created the conditions necessary for the construction of the basement levels within the inner-city building site.
The foundation for the development of a new urban quarter
Using micro piles, large-diameter bored piles, foundation piles and shoring works, PORR special civil engineering carried out a wide range of services on the Telekom site in Konstanz. The special civil engineering works carried out form the basis for the revitalisation of the site and the development of a new residential and commercial location on Lake Constance.
