In order to enable the construction of regular shallow foundations Vibro Stone Columns (VSC) were chosen to reinforce both the granular made ground inside the basement and the cohesive made ground outside the basement. Due to the variability in the made ground Menard advised designing the strip footings to 200 kPa inside the basement and 165 kPa outside the basement.
The design was based on treating to refusal within the basement area (onto the basement floor slab – which was left in-situ) through the dense granular fill assisted by pre-bore, VSC depths ranged from 2.5 m to 3 m in these areas. Outside the basement treatment was taken into the stiff clays to depths in the range of 4 m to 5 m. Settlements were limited to 25 mm total settlements with relative differential settlement of 1/500 maximum. The final design was about 700 stone columns and 2300 m which amounted to a saving of about 20% in embedded carbon on the project.
The works were completed on schedule using 1 VSC rig and 1 pre-bore rig.