Piling contractors Gauteng Piling provided the foundation auger-cast piles for the latest extension to the Cresta Shopping Centre, completed in April, on the border of Northcliff and Cresta, in Johannesburg.
Auger piles, also known as continuous flight auger piles, are deep foundation elements that are cast in place, using a hollow stem auger with continuous flights.
The process is carried out using auger drills that excavate the piling holes drilled into the soil to pre- designed depths. After reaching the required depths, the auger hole is cleaned, and concrete is poured into the hole from a ready mix truck. Reinforcing steel is then lowered into the wet concrete.
The technique is popular globally and used to support a wide spectrum of structures, from towering buildings to tanks, towers and bridges.
“The Cresta contract called for 113 auger piles, ranging from 250 mm to 1 050 mm in diameter, and depths that varied from 6 m to 7.5 m. “Gauteng Piling employed the . . . Williams LDH digger [auger machine] with 5.5 t/m torque and a Soilmec RTAH hydraulic drilling rig,” notes Gauteng Piling contracts manager Martin Eygelaar.
He notes that, after the piling operations had penetrated the first layer of rock at the Cresta site, a high level of underground moisture was encountered, which posed an unexpected challenge for Gauteng Piling.
“This meant we had to revert to the ‘drill-and-cast’ piling method, which substantially speeds up routine auger piling operations to cope with the fact that the pile bore cannot be sealed against water ingress.
“For our ‘drill-and-cast’ operations, a concrete truck was on standby right next to the drill rig. When the flight had reached the required depth, the operator immediately lifted the extracted soil to the surface, and concrete was then hastily cast – within seconds, in fact – to prevent water ingress and the piles from collapsing,” explains Eygelaar.
The main contractor for the Cresta extensions is privately owned multidisciplinary construction group NMC, which has employed Gauteng Piling’s foundation services for various other contracts in the past, including the Peglerae Hospital, in Rustenburg, and the extensions to the East Rand Mall, in Boksburg, which NMC is currently constructing.
Other recent foundations provided by Gauteng Piling include the piling for a new City Lodge hotel, in Newtown, as well as for extensions to the Market Theatre complex, also in Newtown, the large-scale Value Logistics warehouse, in Kempton Park, the Fire & Ice Hotel, in Pretoria, The Grove Shopping Centre, in Pretoria, and the Bon Accord Police Station, also in Pretoria.