International Construction - April 2014 - page 41

41
april 2014
international
construction
TUNNELLING
Unique challenges
>
T
here is no ‘one size fits all’ approach to tunnelling, as each
contract presents unique challenges from tough ground
conditions to extreme remoteness and even poor weather
conditions.
The tools needed often have to be customised for the task at
hand, and specialisednew excavation, lining, drilling andboring
equipment is being developed for the sector all the time.
The real beasts of the tunnelling sector are of course the
tunnel boring machines (TBMs), which are tailor-made to the
project they have been commissioned for, with new technology
developed and integrated tofit demand.
Robbins, for instance, designed a hybridTBM for work on an
inclined tunnel at a mine in Australia.The 8m diameter single
shield earth pressure balance (EPB) machine was dubbed a
hybridbecause it combines features of twoTBM types –EPB for
softer ground, and a hard rock Single Shield.
TheTBM can operate in pressurised EPBmode using a screw
conveyor for soft to mixed ground under water pressure. The
cutterhead allows for interchangeable cutting tools, and in hard
rockmode, the rock is picked up by paddles that load the screw
conveyor, as themachine is operating non-pressurisedmode.
TheTBMwas built usingRobbins’OnsiteFirstTimeAssembly
method inorder tofit within a tight project schedule – a process
that took place at the remote jobsite nearMoranbah, Australia,
and took about four and a halfmonths to complete.
But things don’t always run quite so smoothly. Robbins
also spent some of last year helping rescue a 2.6 m diameter
Caterpillar EPBTBMwhich became stranded underneathNew
York harbour, US, in the wake of Super Storm Sandy, which
Unique challenges
Tunnelling projects presentmanufacturers and contractorswith technical
difficulties that require dedication and innovation to
overcome.
HelenWright
reports.
Amassive,
91.4m long,
17.5m diameter
TBM known
as Big Bertha
has been
stranded 18.3
m underneath
Seattle, US,
since December
last year, with
repairs estimated
to take six
months ormore.
Robbins helped
rescue a 2.6
m diameter
Caterpillar EPB
TBM. which
became stranded
underneath New
York City harbour,
US, in thewake
of Super Storm
Sandy, which
struck the East
Coast in the
autumn of 2012.
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