Estrel Tower Berlin: Combined pile and slab foundation 

CDM Smith has been involved in the project since 2016 and is responsible for the subsoil inves­ti­ga­tion, the subsoil assessment and the design of the foundation. After intensive variant inves­ti­ga­tion, the foundation concept was narrowly decided in favor of a combined pile and slab foundation to avoid major defor­ma­tions.

The subsoil investigations of the area were carried out with boreholes down to a depth of 60 m. A rarely explored layer of the Holstein Warm Period was found under the expected and well-known sands and glacial till at a depth of about 50 m. Due to its composition (organic soils, clays and silts with augers, fluvial sands and gravels), this layer had to be considered with regard to the settlement prognoses and the foundation planning.

The verification of the combined pile-slab foundation was carried out in combination and on the basis of a structural model created by the structural engineer and a geotechnical model created by CDM Smith (G-model, created with PLAXIS®). As a result, the planning is based on a combined pile and slab foundation with 52 large-diameter drilled piles (length: approx. 20 m, diameter: 1.80 m) and a 3.60 m thick base slab.

In the meantime, the piles have been produced, the trough excavation pit has been drained and excavated and the extensive measuring equipment for monitoring the stresses and defor­ma­tions in the ground during construc­tion has been installed. Since April 2022, the base slab has been reinforced and concreted. After that, the tower will rise upwards. The hotel is scheduled to open in 2025. From the outdoor terrace of the Skybar, visitors will have a fantastic view over the capital.