Water, Sewage & Effluent September October 2018 | Page 21

Water Sewage & Effluent September/October 2018
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technology
was tasked with excavating, installing,
and backfilling 1  200m DN  900 HDPE-lined
concrete pipes at depths of between two
and nine metres on a bidim-wrapped 19mm
stone bed and cradle, as well as excavating,
installing, and backfilling 2  485m DN  1200
HDPE-lined concrete pipes between four
and nine metres deep on a bidim-wrapped
19mm stone bed and cradle.
“The DN 1470 HDPE-lined concrete pipes
that went through Macassar Road were
installed at depths of between four and
six metres and required pipe jacking,” he
says. “We were also required to weld the
HDPE capping strips to seal the HDPE-lined
pipe joints and construct 49 in situ cast,
watertight concrete chambers of 3  600mm
in length by 3  100mm in width, with either
2 600mm or 1 800mm precast rings as well as
interim and top slabs, between two and nine
metres deep,” he adds.
The existing siphon structure had to
be demolished and replaced with a new
watertight siphon-connecting chamber, while
the remainder of the work included breaking
into an existing live concrete chamber to
connect the new DN  1200 pipeline; coating
all internal surfaces of the new structures
to protect the concrete against biogenic
corrosion; and shoring/battering of pipe
trenches to protect adjacent infrastructure
and services, all while working in restricted
working widths, Reed adds.
Included in the contract was connecting
the existing live sewer systems to the new
main outfall sewer, as well as modifying
existing structures to accommodate the
new or relaid sewer pipes up to DN 400.
Construction included a new DN  250
uPVC treated sewage effluent (TSE) rising
main of 900m in length; a new DN  250
uPVC pressurised water main of 350m in
length, and connecting the new water
and TSE pipelines to the existing relevant
reticulations.
“Bulk earthworks were necessary to lower
the ground level of the identified areas,
necessitating the temporary relocation of
fences and minor structures,” Reed adds.
Once everything is completed, the pipes,
manholes, and joints will be tested to ensure
that they are liquid-proofed.
Reed concludes that the proudest moment
was: “Actually completing a very challenging
contract with above average quality and
project specifications. Backfilling of the
trenches and chambers in December 2017
and the completion of the pipe installations
and chambers in April 2018,” he beams. u