*Contributors: CESA, Corestruc,
and QC4 Civils.
thickness of 450mm. The structure
features a 700mm diameter inlet pipe,
two 800mm diameter outlet pipes, a
600mm diameter scour pipe, and 800mm
diameter reservoir overflow pipe.
From the outset, it was decided
that the roof of the structure would
be constructed with precast concrete
elements to save time on the
construction programme, in keeping
with the urgency of water infrastructure
being built.
The project cut eight months off the
construction programme, allowing the
reservoir to be delivered in 11 months.
The reservoir roof comprises more
than 2 300m 2 of slabs, each up to
250mm thick. They are supported by 16
columns and 18 beams, weighing 12.3
tons and 7.5 tons, respectively. These
were manufactured by Corestruc and
stored before delivery to site, ahead
of installation in February, which
commenced when 80% of the walls had
been cast.
The construction of the reservoir
wall alone was an impressive
achievement, fast-tracked with a new
climbing system designed and supplied
by Form-Scaff, the civil engineering
“Water is almost
more important than
nuclear at this stage.”
Elsie Snyman, presenting
the CESA report.
Water Sewage & Effluent July/August 2017
Precast concrete elements being positioned.
contractors. In as little as two weeks,
747m 2 per section could be erected, as
opposed to the initial plan of 200m 2 per
section.
Construction of the wall and
installation of the post-tensioning
system followed the installation of the
internal pipes, pouring of the reinforced
concrete foundation, installation of
load-bearing pads for the wall, and
completion of the subsurface drainage
system. This programme was divided
into three sections and four lifts. The
floor slab had also been cast, while
the bases and plinths were ready to
receive the columns.
Equipped with a state-of-the-art
theodolite, Corestruc’s team lifted and
fastened the components into place,
achieving tolerances of about 20mm at
heights of 15 metres.
A total of 2 000m 2 of precast items
were installed in eight working days
— a feat Corestruc’s Willie de Jager
attributes to the extensive upfront
planning.
Once Corestruc had completed
its operations, the civil engineering
contractor’s team started installing
water proofing and covering it with a
stone layer. They installed the tendons
and commenced tensioning, followed
by grouting. A lightning protection
system was installed, and the
reservoir cleaned and inside surfaces
chlorinated before filling the structure
and undertaking waterproof testing.
An added benefit of Corestruc’s
technology is the high durability of the
roof, with all the elements manufactured
from a 55MPa concrete — far
exceeding the 40MPa specification of
the in situ material. This contributes to
the overall performance of the asset,
reducing maintenance requirements of
the structure and costly rebuilds. u
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