36 / 64
34
CONSTRUCTION WORLD
NOVEMBER
2015
'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 overhead crane into the micropile anchors for added
stability. Ultimately, each micropile reached a depth six metres below
the pile toe and were grouted at 40 Mpa at a final depth of 20 metres,"
Tshivhinda added.
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. To accommodate the wide cages,
900 mm diameter piles had to be drilled by Gauteng Piling, which used
two of its Williams diggers for the Kagiso contract.
Prior to the start of the piling contract, the company commissioned
by the contractors to handle the geotechnical investigations had drilled
four large diameter auger trial holes in a grid pattern on the site, spaced
about 30 m apart, with a Soilmech hydraulic drilling rig hired from
Gauteng Piling. "The holes were drilled to refusal on very soft, to soft,
basaltic lava rock and showed that the maximum depths that could
be reached before refusal were from 9,1 metres to 13 metres. Ground
water was encountered at a depth of 11 metres, and therefore Gauteng
Piling had to employ the drill-and-cast method of piling for the entire
contract. This form of piling calls for a concrete truck on standby right
next to the drill rig so that concrete can be cast immediately after the
drilling flights are extracted to the surface. This prevents water ingress
and collapse of the piles," she stated.
PROJECTS AND CONTRACTS
The contract, awarded to the MBA North member company
by the developer, BUA Africa Properties, called for 100 auger
piles with an average depth of 13 metres to serve as foun-
dations for the 240-unit Kagiso residential development in
Margaret Avenue, Kempton Park.
Rofhiwa Tshivhinda, site manager for Gauteng Piling, says the piles
– spread over an area of 3 000 square metres on which an existing struc-
ture had been demolished - were successfully excavated and installed
by the company over a five-week period.
"For a multi-storey building of this nature, rising high above neigh-
bouring structures – and therefore subjected to high structural bending
and horizontal forces – exceptionally strong piling was required. It was
therefore decided that the two lift shafts, on extreme ends of the apart-
ment block, would act as shear walls to stabilise the entire building.
This meant that these two lift shafts had to have piles providing
the utmost foundations and stability. It was therefore decided to
strengthen the 18 piles underneath the lift shafts by inserting five addi-
tional micro-piles (piles-within-piles, so to speak) into these structur-
ally critical foundation elements. The micropiles were drilled through
Project requires
PILES-WITHIN-PILES
Leading piling contractor, Gauteng
Piling, had to provide unusually intricate
and robust foundation piling for the
construction of a new 11-storey apartment
block in the Kempton Park CBD.
>
LEFT:
Exceptionally long steel
rods were lofted over the piles
by overhead crane and then
manually guided deep into place
into the micropile anchors for
added stability.
ABOVE:
Each micropile reached a
depth six metres below the pile
toe and were grouted at 40 Mpa
at a final depth of 20 metres.
Pictured: grouting being poured
into a micropile.
RIGHT:
Steel rods inserted into
micropiles.
"For a multi-storey building of this nature, rising
high above neighbouring structures – and therefore
subjected to high structural bending and horizontal
forces – exceptionally strong piling was required.