Housing in Southern Africa October 2015

Cement & Concrete

Deep foundations for 11-storey residential block Leading piling contractor, Gauteng Piling, provided intricate and robust foundation piling for the construction of a new 11-storey 240 unit residential apartment block in Kempton Park’s Central Business District.

T he main building contractor, BUA Africa Properties con- tracted Gauteng Piling to pro- vide 100 auger piles to an average depth of 13 m, which serves as the foundation for the Kagiso residential development in Margaret Avenue, Kempton Park. Gauteng Piling Site Manager, Rof- hiwa Tshivhinda says that the auger piles covered an area of 3 000m². It took five weeks to install the piles after the existing structure had been demolished and the site cleared. “A multi-storey building of this nature, towers over neighbouring structures and requires exceptionally strong piling to meet the high struc- tural bending and horizontal forces. The specifications included two lift shafts on either side of the apartment block would act as shear walls to stabilise the entire building. Gauteng Piling used 18 piles underneath the lift shafts by inserting five additional micro-piles (eg piles-within-piles) to support and strengthen the founda- tions. The micro-piles were drilled through 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 the overhead crane into the micro-pile anchors for ad- ditional stability. Each micro-pile was inserted to a depth of 6 m below the pile toe and were grouted at 40Mpa at a final depth of 20 m,” said Tshivhinda. 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. The tensile strength of these cages for the lift shaft piles are almost four times stronger than the steel used for the rest of the piling cages on the project. To accommodate the wide cages, 900 mm diameter piles were drilled using two Williams diggers. Prior Gauteng Piling’s contract, the main contractor commissioned a

Gauteng Piling had to employ the drill-and-cast method of piling for the entire contract. This form of piling calls for a con- crete truck on standby next to the drill rig so that concrete can be cast immediately after the drilling flights are extracted to the surface.This pre- vents water ingress and collapse of the piles,” said Tshivhinda. Gauteng Piling, established by Nico Mass, a leading Master Builders SA industry stalwart and MBA North member, will celebrate its 20th anni- versary next year. Gauteng Piling has in the past 19 years completed over 1 500 projects and is now one of the major players in the piling industry. ■

company to handle the geotechnical investigations. This resulted in four large diameter auger trial holes being drilled in a grid pattern, spaced 30 m apart. “The holes were drilled to refusal on very soft, to soft, basaltic lava rock and showed that the maxi- mum depths that could be reached before refusal were from 9.1 m to 13m. Groundwater was encountered at a depth of 11 m and therefore

October 2015