A systematic geogrid installation by South African World Cup 2010 contractors overcame poor load-bearing ground encountered on the new Green Point Stadium in Cape Town (“Cape Town Stadium”).
Construction of the stadium, which will play host to a World Cup semifinal in July, was made problematic by the highly variable soil inherent to this scenic oceanside setting near the southern tip of the continent.
The new 68,000-seat stadium was originally designed set into a deep excavation, to satisfy planning constraints related to nearby buildings. Initial problems were encountered as a result of the excavated material placed uncompacted over surrounding spaces. So, when temporary, construction haul roads for access were routed over these areas, considerable ground movement was experienced.
Because some of these roads would later become permanent for stadium access, the routes needed stabilization. The decision-making became a choice of removing 6-8m of the fill, replacing it with properly compacted fill, and bringing it up to level; or constructing a mechanically stabilized earth (MSE) road base with two layers of geogrid and 400mm of locally-sourced, high-quality aggregate.
The use of geogrids reduced both time and cost and this solution was deemed a success following extensive use during an exceptionally difficult winter. Even severe rain, including a 58mm (2.25in.)/hour storm, resulted in minimal settlement or deformation of the new access road.
These results prompted the contractors to also utilize localized load-bearing support for other parts of the stadium:
- Geogrids were installed to reduce the required thickness of the proposed aggregate fill in the upper layers of the “Grand Staircase,” speeding the construction and saving on imported aggregate.
- At another point of the Grand Staircase, geogrids were used to reinforce the bedding under the steps and reduce any differential settlement that could compromise the structure and require remediation.
- Finally, a geogrid mechanically stabilized layer was installed beneath the capping “jockey slabs” for the concrete retaining walls, to mitigate any differential settlement between the slabs and the fill where the stadium-site landscape slopes away towards the sea.
Total construction time for the new stadium was 33 months.