Construction World April 2016

CONSTRUCTION WORLD

APRIL

2016

GEOTECHNICAL ENGINEERING

Kobus Geyer, site manager for

Gauteng Piling, says the contract

for the piling – required to erect

a new five-storey parkade on the

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-

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

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.

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.

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.