Construction pit planning at the Sophienkontor building in Kiel

The property in the center of Kiel is just a stone's throw away from the Kieler Förde inlet, the main train station and the former state central bank building. In a spirit of excellent and friendly cooperation with the client via urban space from Hamburg, on-site design planning of the construction pit was optimized and streamlined by PORR Spezialtiefbau Planung while simultaneously gaining more enclosed space.

Sustainable optimisation

The original plan was to construct a one to two-floor basement for the new building with a large number of bottom drops and area-by-area pile foundations, to be enclosed by an on-site designed, overcut, back-anchored bored pile wall (width = 80cm with a 10cm overcut to secure the excavation).

With our optimisation proposal for a two-phase diaphragm wall (width = 60cm) and a second full basement level, it was possible to gain a large amount of usable space in the 2nd basement, while reducing concrete usage for the support by almost 20%. There was also no longer any need to dispose of demolition waste and soil from the overcut holes in the originally planned bored pile wall and any foundation piles.

The speedier production process for the diaphragm wall compared with the time-consuming production of an overcut bored pile wall was also a welcome bonus.

Precise representation using 3D technology

Due to the limited available space and neighbouring buildings on three sides (some of them of historical significance), planning was also carried out at the highest level using 3D technology.

This had a number of advantages, especially in the representation of the grouted anchors under the neighboring buildings with pile foundations, as collisions are effectively avoided in this way and inclination and swivel angles can be specified to the exact degree.

There are also advantages for the internal diaphragm wall corners, where the anchors have to be guided into the same soil body from two directions without overlapping.

Conserving resources with construction planning

We worked closely with the IGB engineering consultancy in Kiel to conserve resources,. Their probing work made it possible determine the exact position of the sealing marl layer. These findings helped to reduce diaphragm wall lengths on a larger scale.

While ensuring the minimum embedment depth, it was possible to precisely align the bases of the diaphragm wall with the subsoil layer so they could be placed higher overall. The bases of the layer established during the construction phase confirmed the previous optimization, depicted here as a step-like development in the image from PORR.