The Civil Engineering Contractor April 2018 | Page 19

ON SITE
Concrete bases being poured. The perimeter wall showing graded groundworks and the contractors preparing the sheer wall
to Sable Park, the architectural firm
also got the Axis residential project,
which is currently under construction
on the plot next door.
Challenges
With such a complex design, there
were numerous challenges across a
number of sectors.
Given that the site is located in a
well-developed area, lateral stability
in the form of soldier piles in the
basement had to be provided to
ensure that there was minimal impact
on the existing surrounding roads —
Sable Road and Energy Lane — while
excavating the basements.
To account for the transition from
the regular column spacing in the
basements and the larger, irregular
spacing of columns on the ground
floor, transfer beams were built on the
ground floor.
The ‘staggered’ effect between floors
required designing large cantilevers,
without the structure impeding on the
architectural intent. A post-tensioned
slab system was used to account for the
large cantilevers.  
In the entrance atriums, supports
for the facades had to be seamlessly
incorporated into the architectural
design of the façade, with steel
columns and beams being used. In
addition, these steel elements had
to be connected to the existing
concrete frame with minimum
effects on the aesthetics.
Environmental
management
challenges included dealing with large
quantities of excavation water during
the installation of the basement levels.
This water had to be settled and filtered
before leaving site via the stormwater
system to prevent negative downstream
impacts owing to sedimentation or
pollution. Sound waste management
practices as well as reducing dust,
pollution, and nuisance impacts are also
top priorities for the environmental
management team on site.
Despite the extensive amount of water
on site, Basson explains that it was
found to be unsuitable for construction
purposes. “I’m not the expert on
this, but the concrete for building
the columns and decks was done off
site, premixed, and delivered to site,
so we don’t know what their water
source was. With concrete and rebar,
you cannot really use ‘alternative’ water
as you do not know the purity or
chemical/mineral content of the water
supply, which can adversely affect the
concrete or steel,” he points out.
Regarding the effects of the drought,
Basson says that before 2018, contractors
had to apply for a water permit to use
the municipal water on site. Fortunately,
he points out, it was during this phase
that the building was constructed. “It
was strict, but permissible, so long as
the correct channels were followed,” he
comments. Whereas 2018 is “dire” by
way of access to water, according to the
engineer. “I assume that going forward,
alternative water for construction is
going to come under the spotlight, with
much research and study carried out, to
ascertain under what conditions it can
be used,” he muses.
He adds that tests were conducted on
the groundwater source to see whether
it could be used for flushing toilets,
but the mineral content was too salty.
Desalination would not have been the
solution owing to the volume of water
consumption versus cost of plant, as
well as the costly adverse effect the
solution would have on filters, he
points out.
Environment
Sable Park has been designed and
managed such that it can be awarded
certification by the Green Building
Council of South Africa. The developers,
Rabie Property Group, with the
assistance of Green Star certification
consultants PJ Carew Consulting, are
targeting a five-star rating.
Ecosense environmental consultants
were appointed to design and oversee
the implementation of a Construction
Environmental Management Plan
(CEMP) for the project, which would
both contribute towards achieving the
overall Green Star target rating and
CEC April 2018 - 17