The clean coal storage silos at Rio
Tinto’s Mount Thorley Wark
worth mine, located near Single
ton, are a crucial to the productivity of
the whole operation.
circumferences of 48 m, are designed
to store up to 3000 tonnes of coal before
it is transported by rail to the Port of
1984 with a single 250 mm layer of
construction was completed, cracks
became visible on the external faces of
tensioned steel cables horizontally
around the silos in order to restrain the
walls against the coal loading and prevent
for some time, they eventually began
to corrode and fail.
decrease steadily every year, so the mine
sought out Newcastle-based engineer
ing firm Izzat Consulting to propose a
more long-term solution.
corp Asset Solutions was commissioned
in 2008 to carry out the repairs.
store 25% of their total capacity.
Brendan Walsh, oversaw the $3.2 million
the cables, repair the concrete and then
apply layers of carbon fibre to rein
force the structure,” he told Australian
silos were under-reinforced from the
apply up to four layers of carbon fibre
in continuous 300 mm wide strips.”
neers chose carbon fibre for its high
tensile strength and resistance to corro
the cables, but they would have
inevitably failed again,” he said.
tional while the project was underway,
it was difficult to gain access to the
on two metre high horizontal sections
of the silo at any one time to ensure
we did not weaken the structure in any
way,” he said.
nate between two metre areas at the
top and bottom of the silo.”
recommended the use of scaffolding.
realised this would not be satisfactory.
scaffolding all over both silos would
have been a bit of a headache, because
in some cases it would actually restrict
the working space,” Walsh said.
that much on structures so large.
designed mast climber system, which
reduced the cost by around $300,000
and actually gave us a much better
vertical mast climbing units fixed at
equal intervals around each silo’s circum
ference, as well as separate decks fitted
between each mast.
into six separate working areas and
we could use any one of the decks to
travel up and down the structure,”
together to provide access to the complete
as a climbing workshop.”
safely restrain and remove the cables,
which had tensile forces of 20 kN.
prevent the cables from flying away
from the structure when we cut them,”
removed the damaged concrete with
hydro-demolition, using low volumes
of water at pressures up to 20,000 psi.
with shotcrete to provide a stable surface
for the carbon fibre.
of external crack repairs, 1633 m of
internal crack repairs, 14.42 km of
carbon fibre wraps and two kilome
tres of carbon fibre laminates.
when heavy rainfall and flooding hit
the Hunter region mid-way through
work on the first silo, forcing the site
to be evacuated.
water because the roof had been removed
and one of the post-tensioned cables
actually snapped under the strain of
this extra load,” Walsh said.
and make sure the cables were secured
before we restarted work.”
the silos have been running at full capac
ity and are expected to last another 15
years before further maintenance will
ant to temperature variations, rain and
hail so it only requires minimal main
tenance,” Walsh said.
deterioration, but that can be prevented
by applying a resistant coating to the
fibre could have a limitless lifespan.”