The Civil Engineering Contractor November 2018 | Page 22

ON SITE
taken into account protection of a
major 300mm-diameter, 6mm-thick,
existing Sasol gas pipeline operating at
35 bar pressure. “Motheo is working
closely with Sasol and the engineering
consultant to protect the pipeline
during the construction phase,”
says Brink.
On-site challenges
There are currently 50–60 people working on digging 3 500m of stormwater piping,
1 900m of water pipes, and 2 500m of sewerage pipes. The number of workers is poised
to ramp up considerably in the medium term.
Helgard Brink, site agent with Motheo Infrastructure (left), with Tinashe Chapwanya,
resident engineer with FIJ Consulting.
The plan for the 58ha site.
20 | CEC November 2018
Tinashe Chapwanya, resident engineer
with FIJ Consulting, explains that as
much as 80% of the site is underlain
with dolomitic rock, meaning the
residential units could not be built
over those areas — though he says
there is still enough land, given there
are large wetland areas to be retained,
and also considerable general areas.
Dolomitic areas represent a geological
condition whereby specific statutory
requirements govern the geotechnical
investigation, due to the risk of
sinkholes forming underground.
This was duly undertaken on site
and approved by the National
Home
Builders
Registration
Council (NHBRC), which reviews
geotechnical investigation reports for
residential developments.
“We are building residential units
only on those sections which are
not dolomitic — the site has been
designed so that the units are built on
good, solid earth. The roads, ponds,
and trenches will be safely built on
the dolomitic areas,” says Chapwanya.
There is also a substantial quantity
of rock on site. Due to its dolomitic
nature, no traditional blasting could
take place. Motheo opted to use
hydraulic hammers to remove the
rock mechanically. Chapwanya adds
that there is rock throughout the site,
“and all that varies is the level at which
it occurs at each location”.
Another challenge associated with
the site, which at the time of the
interview Motheo was still developing
a solution for, is construction of the
water supply. Municipal supply is not
readily available on site and, given
the volume of construction water
required by the contract, Motheo
was exploring the use of recycled and
stored rainwater among its options.
Motheo has taken good advantage
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