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Thursday, September 09, 2010 |
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Stefanutti Stocks provides lateral support at Sandton Cit
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Source: Marius van der Merwe
Work on site for Phase 1, of the Sandton City Repositioning project, started in January 2009 and the project is due for completion in November 2011.
The excavation of the basement, undertaken by Zero Unlimited Earthworks, required lateral support around the perimeter. The contract for the lateral support was awarded to the Stefanutti Stocks Geotechnical division in May 2009 on a design and construct basis.
“Our scope of work on this project consisted of lateral support and piling,” says Willian du Toit from Stefanutti Stocks. The lateral support and piling increased considerably in value during the project, and this part of the project was completed at the end of April 2010. “During the duration of the project a total of 165 000m3 of material was excavated,” says Marius van der Merwe, “110 000m3 of which was rock.”
While designing the lateral support, our geotechnical engineer, Ken Schwartz, was faced with a number of challenges.
• The existing building was situated approximately 500mm away from the north and west walls of the excavations. Some of the old building’s foundations were piled and some pad footings. The foundations on pad footings required additional active support.
• The excavation depth next to the existing buildings was up to 8.5m. To accommodate this a combination of soil nails, gunite with mesh reinforcing, temporary anchors and whalers were used. Poly fibres were used as reinforcing over the exposed rock faces.
• The south walls next to the boundary prevented the use of permanent anchors or soil nails and the piles had to be designed to carry their load into the new building in the final state.
• The rock level varied substantially, from 5.7m below to 7.6m above the final excavation level. This necessitated the installation of 900mm diameter piles to rock level with anchor dowels at the toe. In very shallow rock conditions the dowels were not sufficient and 380mm diameter mini-piles had to be installed through the 900mm diameter piles to the required epth below excavation level.
• A perched water table on the south wall caused collapse during pile driving and resulted in Stefanutti Stocks using 1 050mm diameter temporary casings to facilitate installation.
Quantities:
Lateral support
• 3 460m2 temporary gunite walls with temporary soil nails, anchors and whalers.
• Piled walls with gunite arches, temporary anchors and permanent dowels at the bottom. 1 385m linear meters of piles installed over an exposed area of approximately 3 405m2.
• 210m2 permanent gunite walls with permanent soil nails.
• A 7 075m2 area of lateral support.
Piling
• Tension piles;
• 1 400 kN 300mm diameter post stress piles;
• 1 400 kN 300mm diameter reinforced tension piles ;
• Mini piles;
• 150mm diameter piles; and
• 300mm diameter piles.
This busy construction site employed 113 people and some impressive machinery including Casagrande B170 and B125 piling rigs, a C8 and two C6 Casagrande crawler rigs, three Comacchio crawler rigs and two Furukawa crawler rigs.
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