Construction World April 2016

GEOTECHNICAL ENGINEERING

Established 20 years ago, Master Building Association (MBA) North member Gauteng Piling, has already completed over 1 500 major piling projects in many parts of South Africa. Included in prestige contracts handled was the piling for the construction of Southern Afri- can’s largest single-phase retail centre, Mall of Africa, now under construction in Midrand, which called for over 500 piles. Other recent contracts handled by Gauteng Piling include the piling for the massive 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. The company also handled the piling requirements for a new FAW auto dealership in Croydon in Ekurhuleni, as well as the piling for exten- sions to the Market Theatre complex in the Johannesburg CBD as well as the I’langa Mall in Mbombela (Nelspruit). 3,7 metres deep, and the diameter of the holes varying between 1 200 mm and 1 600 mm. The steel reinforcement cages for the piles varied between 1 050 and 1 450 mm in diameter. Mota-Engil SA Construction are the main contractors for the erection of the parkade, but Gauteng Piling secured the contract following a direct appoinment by SIP Project Managers. The project started in September 2015 and was completed in about three months. Two piling rigs were initially employed but, as site problems began to mount, the fleet had to be expanded to four: Hendrickson 80 and 120 diggers, an IMT digger, and RTSA Soilmec unit.

PUSHED to the LIMIT MBA North member, Gauteng Piling, had to resort to exceptionally rare measures to cope with extreme rocky terrain encountered while providing the auger piling foundations for the expansion of the Fourways Mall shopping centre, north of Johannesburg.

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Kobus Geyer, site manager for Gauteng Piling, says the contract for the piling – required to erect a new five-storey parkade on the

forced concrete bases which, basically, is the only solution when the ground bearing strata is too deep for traditional piling,” Geyer states. Because of the varying rock bearing strength and depths, it was also decided that the number of piles Gauteng Piling had to provide had to be reduced from 160 to 42. But more problems emerged. “Once these piles were drilled, it was discovered that the bearing capacity of the rock varied from hole to hole. So, to overcome this, smaller flights were used to re-drill all the holes to refusal, i.e. as deep as possible. A rock core barrel was then used to trim the harder rock to the same level. Needless to say, all of these special measures proved extremely time-consuming and frustrating,” Geyer added. The piling operations took place on a 10 950 square metres area with most of the piles

tarred open-air parking area on the north- eastern wing of the shopping mall – produced formidable challenges right from the outset. “We almost Immediately encountered shallow, very hard rock which was to take a heavy toll on our piling rigs and delay the completion of the contract. In fact, as soon as drilling commenced, we knew that the stipulated piling depths were just not going to be feasible. So Gauteng Piling had to commission geological tests of the soil bearing capacity to obtain an indication of the the depth of the rock and, based on the results of the tests, it was decided that 59 holes that we had already drilled had to be converted into mass rein-

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Pictured at the start of piling operations for the extension of Fourways Mall – a project that struck soil so rocky that exceptional measures had to be employed.

CONSTRUCTION WORLD APRIL 2016

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