Work on a new basement in the Swedish city of Gothenburg is claiming to be dealing with the world’s worst ground conditions.
Contractor Peab is working with support specialist Groundforce to deliver the new basement for the Lykholms commercial development on the site of an historic brewery in the city.
The 80m long, 20m wide rectangular basement excavation is relatively shallow, at approximately 3m, but the ground conditions were so poor that robust lateral support was required to restrain the steel sheet-piles lining the excavation.
“The soil conditions were really, really bad – but this is Gothenburg,” said Peab estimator Johan Stenlund. “Gothenburg is notorious for its poor geology – it’s probably among the worst in the world. We have weak glacial clay up to about 100m and really bad compressive strengths – down to around 7kPa.”
The ground conditions were complicated by the fact that the site came within 10m of the Möndals river. Total excavation depth was around 4m and the sheet piles were driven to a depth of up to 14m.
To support the excavation, Peab chose Groundforce’s Mega Brace system, suspended from chains, as a waling beam around the perimeter.
Nine MP150 150t capacity hydraulic props were used to brace the waling beam. Five of the props were located from side-to-side, spanning the 20m wide excavation. The remaining four were installed obliquely across the corners to support the ends of the excavation.
“The modular design helped with the trickiest past of the job from our point of view which was that a section of the northern part of the excavation adjoined one of the existing buildings,” said Groundforce Scandinavian sales manager Sam Oldroyd. “Our modular system meant that we could miss out components in this area to avoid clashing with the building”.
According to Peab, the proprietary temporary works solution saved time and cost over a steelwork frame approach.