Construction World November 2015

PROJECTS AND CONTRACTS

Project requires PILES-WITHIN-PILES Leading piling contractor, Gauteng Piling, had to provide unusually intricate and robust foundation piling for the construction of a new 11-storey apartment block in the Kempton Park CBD.

'Cross Hole Sonic Logging' (CHSL) tubes and extended into the pile cap. "Exceptionally robust 36 mm Thread Bar steel rods (TB950) were then inserted by overhead crane into the micropile anchors for added stability. Ultimately, each micropile reached a depth six metres below the pile toe and were grouted at 40 Mpa at a final depth of 20 metres," Tshivhinda added. All of these relatively voluminous and intricate components were housed in specially-designed 13 m long steel cages, with a diameter of 800 mm and weight of 1,8 tons each. To accommodate the wide cages, 900 mm diameter piles had to be drilled by Gauteng Piling, which used two of its Williams diggers for the Kagiso contract. Prior to the start of the piling contract, the company commissioned by the contractors to handle the geotechnical investigations had drilled four large diameter auger trial holes in a grid pattern on the site, spaced about 30 m apart, with a Soilmech hydraulic drilling rig hired from Gauteng Piling. "The holes were drilled to refusal on very soft, to soft, basaltic lava rock and showed that the maximum depths that could be reached before refusal were from 9,1 metres to 13 metres. Ground water was encountered at a depth of 11 metres, and therefore Gauteng Piling had to employ the drill-and-cast method of piling for the entire contract. This form of piling calls for a concrete truck on standby right next to the drill rig so that concrete can be cast immediately after the drilling flights are extracted to the surface. This prevents water ingress and collapse of the piles," she stated. "For a multi-storey building of this nature, rising high above neighbouring structures – and therefore subjected to high structural bending and horizontal forces – exceptionally strong piling was required.

The contract, awarded to the MBA North member company by the developer, BUA Africa Properties, called for 100 auger piles with an average depth of 13 metres to serve as foun- dations for the 240-unit Kagiso residential development in Margaret Avenue, Kempton Park. Rofhiwa Tshivhinda, site manager for Gauteng Piling, says the piles – spread over an area of 3 000 square metres on which an existing struc- ture had been demolished - were successfully excavated and installed by the company over a five-week period. "For a multi-storey building of this nature, rising high above neigh- bouring structures – and therefore subjected to high structural bending and horizontal forces – exceptionally strong piling was required. It was therefore decided that the two lift shafts, on extreme ends of the apart- ment block, would act as shear walls to stabilise the entire building. This meant that these two lift shafts had to have piles providing the utmost foundations and stability. It was therefore decided to strengthen the 18 piles underneath the lift shafts by inserting five addi- tional micro-piles (piles-within-piles, so to speak) into these structur- ally critical foundation elements. The micropiles were drilled through >

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LEFT: Exceptionally long steel rods were lofted over the piles by overhead crane and then manually guided deep into place into the micropile anchors for added stability. ABOVE: Each micropile reached a depth six metres below the pile toe and were grouted at 40 Mpa at a final depth of 20 metres. Pictured: grouting being poured into a micropile. RIGHT: Steel rods inserted into micropiles.

CONSTRUCTION WORLD NOVEMBER 2015