Challenging soil and groundwater conditions
Following the demolition of the basement of the existing building, a 1,800m2 trough excavation pit with a depth of around six metres was created. As the groundwater level is around three metres below ground level, it is made watertight and sealed with a jet grouting base. The enclosure is made with an overlapping bored pile wall consisting of 240 bored piles as well as a sheet pile wall around 54 metres long.
The heterogeneous soil conditions present an additional difficulty. Below the backfilled surface layers, there are medium-density sands, loosely bedded sands as well as organogenic soil types. An approx. 50 metre wide and up to 12 metre deep organic trench made of peat runs through the middle of the construction site. Soil improvement is therefore carried out with 168 Atlas columns and 210 DSV columns.
Challenging construction site in a listed ensemble
The L-shaped new building is in prominent architectural company. Pariser Platz is located at the end of the boulevard ‘Unter den Linden’ directly in front of the Brandenburg Gate. Many Bundestag buildings as well as embassy buildings are just a few steps away. The Schadowhaus, built in 1805 and the oldest surviving neoclassical building in the former Dorotheenvorstadt district, is its immediate neighbour, so the special foundation engineering work must be carried out with minimal vibration. In order to prevent deformation of the construction pits, the excavation pit is braced with steel structures and the Schadowhaus is underpinned with back-anchored jet grouting. For safety reasons, the entire specialised foundation engineering work will be closely monitored by vibration and settlement measurements on the surrounding buildings.
‘The sensitive, city-centre location in the middle of a listed ensemble requires the utmost care and flexibility during the specialist foundation engineering work. Previously unknown existing pipelines run through the construction site, so we had to construct various temporary pipework. Last but not least, the cramped conditions are a challenge, as several large pieces of equipment as well as the articulated lorries for transporting the soil to and from the site have to be coordinated in this exposed location in the middle of Berlin,’ explains project manager Theo Jentsch.