Historic piling method to preserve C.B.D. heritage
Leading piling contractor, Gauteng Piling, resorted to an age-old piling technique to cope with space restrictions and heritage preservation when providing the foundation elements for extensions to the Market Theatre complex in Newtown, Johannesburg.
The Market Theatre Foundation commissioned the alteration and demolition of some of the buildings on a city block bounded by Bree Street to the north, Miriam Makeba Street on the east, and Margaret Mcingana Street on the west. The new development, east of Mary Fitzgerald Square, will provide additional facilities for the Market Theatre precinct, including a new theatre, rehearsal rooms, library, gallery space, classrooms and offices. It has been designed by KMH Architects.
The construction site is located among some early Johannesburg buildings and facades, including Schlom’s Eating House and the Graffiti Building.
Schlom’s Eating House dates back to 1914 and has, according to leading heritage consultant, Herbert Prins, ‘strong social significance’. In this ‘eating house’ black and white people dined together when restaurants were legally prevented from serving mixed races. Graffiti Building, a grain warehouse before its walls were over time adorned with graffiti by talented street artists, was built a few years after Schlom’s.
Gauteng Piling, was sub-contracted by the main contractor, Solidaire Construction, to provide 73 auger cast piles and 14 bored piles, varying in depth from 8 to 12 m and 250 mm to 850 mm in diameter, on the development site of about 2 000 m2.
Martin Eygelaar, Gauteng Piling contracts manager, said because the Market Theatre Foundation planned redevelopment of its property to preserve these historic buildings, particular piling precautions were essential to avoid damaging the heritage structures.
“The piling required within the confines of Schlom’s Eating House, in particular, proved particularly challenging and required returning to the historic ‘pile-driver’ method.
“We utilised a bored piling rig, equipped with an 800-kg hammer, which was dropped from a height within the building itself to create 14 holes, between 6 and 7 m deep, and 410 mm in diameter. Reinforcing steel cages were placed in the holes, which were then filled with concrete. Using the ‘old-fashioned’ compact rig was essential because a normal rig wouldn’t have fitted within the building,” Eygelaar added.
The drop hammer technique is the simplest and most frequently used to install concrete piles. The traditional type of pile driver comprises a heavy weight (drop hammer) placed between guides to slide freely up and down in a single line. The weight is raised, now with diesel power (previously with animal or human labour); when it reaches the top, it is dropped to smash on to the pile to drive it into the ground.
Although not commonly used today, drop hammers, weighing up to 5,000 kg, can be very accurate, something essential for the Market Theatre project.
For the rest of the auger piling holes required, Gauteng Piling used Williams Digger LDH and Williams Digger MF rigs, which are exceptionally fast, mobile and reliable, with some models capable of drilling 18 m deep.
Adds Eygelaar: “The piling outside the heritage buildings was simpler, although we encountered underground water which necessitated using the drill-and-cast method instead of auger piling to prevent collapse. Drill-and-cast operations require a concrete truck on standby right next to the drill rig. When the rig has reached the required depth, the operator immediately lifts the extracted soil to the surface and concrete is cast – within seconds – to prevent water ingress and the piles collapsing.”
Established 18 years ago, Gauteng Piling has completed almost 1,500 major piling contracts and has attained 135% BBBEE recognition.
Among its many contracts, the company recently completed the piling for construction of southern African’s largest single-phase retail centre, Mall of Africa, which required over 400 piles.
More information from Hennie Bester, cell: +27(0)82 651 8184 / www.gautengpiling.co.za
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