Client: De Weger Architecten and Ingenieursbureau (now Royal Haskoning BV).

Challenge: The slurry wall installation of a 23-meter deep excavation for the Rokin Station in Amsterdam had to be assessed for its structural integrity. Insight needed to be obtained in:

• Settlements at the surface and below due to the installation process and subsequent excavation including dewatering
• Ground water level changes resulting from dewatering inside the building pit
• The risk of bursting of the building pit if dewatering was to be discontinued before the concrete floor of the metro station had been installed

Method: A two-dimensional, fully coupled pore fluid flow – stress analysis including all phases of the building process, and a potential failure of the installation of the concrete floor was carried out modelling the following building phases

• Installation of the slurry wall
• Seven steps of:
  • Excavation
  • Dewatering
  • Installation of supporting struts
• Installation of the building floor
• Discontinuation of dewatering, this step has also been simulated without concrete floor

The analysis model contained dedicated soil material models tailored to the current ground conditions, including the permeability to accurately describe consolidation and ground water flow over time.

Result: It was found that:

• The prediction of the surface settlements were a close match to reality providing confidence in the modelling techniques applied.
• It was demonstrated that stopping dewatering for a two month period would, in principle, be acceptable, which provided a good understanding of the ‘what-ifs’ when the project is delayed.
• Stresses in the slurry wall were within acceptable values throughout the building process.

Value: An increased confidence in the applied building method and risks. The Rokin Station has since been build successfully