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Foundation and excavation, Roche Building 1, Basel

Roche plans to erect an office tower with a height of 178 meters on its main site in Basel. The 22 m deep excavation adjoins the existing laboratory and office buildings directly on three sides. The concept for the excavation makes provision for a watertight secant pile wall retained with up to four anchor layers. Thanks to vertical anchor tests carried out in advance, it was possible to greatly increase the usual anchor capacity applicable in Basel, thus saving approximately 200 anchors – with significant benefits in terms of cost and scheduling.

Complex deformation calculations using the finite element method (FEM) were undertaken to estimate the influence of the excavation on the 62 m high adjacent construction.

For a safe and economical transmission of the loads from the high-rise building into the subsoil, provision is made for a piled raft foundation that optimally exploits the foundation raft and the 143 large bored piles to minimize deformation of the high-rise building and induced settlement of the adjacent construction. Tridimensional non-linear finite element calculations allowed realistic forecasting of the load-bearing behavior of the piled raft foundation and also correct estimation of the overall subsidence (of about 2-3 cm). Extensive monitoring of the foundation as well as the excavation indicated that the measurement results were well in line with the forecasts.

Services provided by Gruner Ltd Geotechnical Engineering Department comprise:

  • Preliminary study, basic design, tendering, detailed design, building inspection for the excavation and piled raft foundation.
  • Deformation forecasting for the excavation wall, the foundation and the neighboring buildings following excavation of the pit, dewatering, installation and prestressing of the anchors, piling work and construction of the high-rise (3D finite element method (FEM)).
  • Support, analysis and back-calculation of static and dynamic pile tests.
  • Monitoring the excavation, also monitoring the piled raft foundation (for many years).
  • Securing the directly adjacent construction that is sensitive and has shallow foundations; this includes a 19-storey high-rise office building.
  • Seismic analysis for the foundation and excavation.

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