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Auckland entrepreneur Daniel Coats set up Helix Flight Machine
Manufacturing to overcome that problem.
A typical modern screw-pile consists of a steel tube with one or
more single-turn helixes (or flights) welded on to the tube. Like a
large disk, the helix spreads axial loads from the tubular pile to
the surrounding earth. This means screw piles can resist both
compression and tension loads, as well as overturning moments and
side loads. They are a popular choice for structures like
electri-cal transmission towers and wind turbine towers, and they
work well in marine applications. According to Mr Coats,
THE TURN OF THE SCREW
screw pile foundations in Christchurch out-performed other types
during the 2010/2011 earthquakes and because they can be driven in
tight, awkward spaces without traditional brute force pile-driving,
they are an attractive option for underpinning existing
structures.
Screw-piles are driven into the ground using a hydraulic drive
system not unlike a scaled-up battery screwdriver: A hydraulic
motor forces the pile to rotate, while a hydraulic ram applies a
carefully calibrated vertical force. This drive system is usually
mounted on a digger. Often, the system can drive the piles at any
angle between horizontal and vertical.
SCREW PILES CAN SOLVE MANY INTERESTING PROBLEMS. BUT HIGH
QUALITY IS IMPORTANT, AND IN SOME PARTS OF THE WORLD, HIGH-
QUALITY SCREW PILES CAN BE HARD TO GET.
Writer Kevin Cudby
This means screw piles can be used for bracing and for retaining
walls, as well as for ordinary foundations.
The quality of a screw pile foundation depends on the quality of
the helical flight. A good screw pile, correctly driven, will
advance exactly one pitch per turn. This minimises ground
disturbance: the helix can only disturb the ground along its own
path. If the pile has multiple helixes, each helix precisely
follows the path of the previous one. To achieve this, the pitch
angle must be uniform, all radial lines across the helix must be
per-pendicular to the shaft and the inside and outside of the helix
must be circular. If the
CIVIL STRUCTURAL
26 Engineering Insight Volume 15/6
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helix is badly shaped it may weaken the ground, or perhaps even
tear it up, like a bolt stripping the thread out of a nut.
Screw piles are not usually available off-the-shelf. They tend
to be designed and built for specific project requirements. Screw
pile manufacturers tend to concentrate on local markets, sometimes
offering products designed with local conditions in mind. For
example, some North American manufacturers specialise in piles for
frozen ground. Manufacturers tend to use home-built machinery for
cutting and forming flat steel plate into helical flights, which
resemble large outside diameter radial split washers.
Mr Coats says the trick is to make a perfect helix. Helix
quality around the world varies quite significantly. Screw piles in
New Zealand are excellent, but in other parts of the world, helix
quality varies from reasonable to pretty bad, invalidating many
screw pile designs.
Mr Coats has been involved in the screw pile market for more
than 15 years. In 1998 he established a company called Piletech to
produce screw piles for the New Zealand market. While developing
Piletech, he regularly communicated with
The new machine would be precise and sophisticated, but no one
would ever call it dainty. The biggest version can form helixes up
to four metres in diameter from steel plate up to 40 millimetres
thick. However, the biggest chunk of the development budget was
spent on the computer control system. That required some pretty
complex software, Mr Coats says.
Research and development funding from Callaghan Innovation
helped bring the project to fruition. Callaghan Innovation provided
50 per cent of the $10,000 dollars budgeted for the initial
feasibility study, followed by another grant covering 40 per cent
of a six-figure development programme. A lot of companies are doing
good R&D, but they arent getting Government funding, Mr Coats
says, adding that Callaghan Innovations application process is time
consuming. Once you jump through the bureaucratic hoops, you can
get access to R&D money.
The result of all that research and development was the Ultra
Adjustable Helix Forming Machine, for light, medium and heavy-duty
applications. The light-
Opposite: Manufacturing screw piles. Photo: Piletech.
Left: Installing screw piles on site at Hutt Hospital in
Wellington. Photo: Piletech.
overseas screw pile manufacturers. After Piletech was sold to
Fletchers, Mr Coats was able to think about international
opportunities.
In 2012 he set up Helix Flight Manufacturing Machines Limited
(HFMML) to develop and manufacture the ultimate helix cut
predicting software and forming machine technology. This was not as
simple as it sounds. Most screw piles are tailor-made. Engineers
adjust parameters such as the size and pitch of the helix to suit
specific ground conditions and structural requirements. Sometimes,
a project may need several different types of screw pile to suit
variable ground conditions, or because different parts of the
structure put different loads on the piles. The HFMML machine had
to be easily and quickly programmable to make custom-designed
helixes with very precise geometry.
SCREW PILES IN NEW ZEALAND ARE EXCEL-LENT, BUT IN OTHER
PARTS OF THE WORLD, HELIX QUALITY VARIES FROM REASONABLE
TO PRETTY BAD.
November/December 2014 27
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Below: Demonstration of the loads working on the upper helix
surface during installation. Image: Helix Flight Manufacturing
Machines.
duty and medium-duty versions are most in demand, Mr Coats
says.
The company began shipping com-plete machines earlier this year
and all the machines they have made so far have been sold to
overseas customers, including in Japan and North America. They are
also developing a simplified, less adjustable machine for high
through-put production of standardised piles. Alongside its
machines, the company provides software for designing the blank
ready for forming.
The adjustable machines deliver more than just superior helix
quality. Compared with existing technology, Mr Coats says they are
easier and faster to set up, which dramatically improves
manufacturing efficiency. In addition, because they pro-duce
helixes with very consistent pitch form, it is easy to automate the
welding process, eliminating a potential source of human error.
Screw pile manufacturers are not the only people checking out
the machines. According to Mr Coats, the technology is popular with
firms that make sectional helixes for a range of products such as
augers and industrial conveyors.
Mr Coats is embracing the challenge of earning a return on the
R&D investment. He anticipates strong demand for the machines
because of growing interest in screw pile foundations. Although
screw piles with cast-iron tips and wooden shafts were popular in
the 19th century, they fell out of favour in the early 20th
century. The development of hydraulic
machinery has revolutionised the field, Mr Coats says.
The modern tube and plate screw pile performs well in many
situations where ordinary piles fall short. The large-diameter
helix makes them ideal for use in weak soil such as marine
sedi-ment and their ability to resist vertical forces has made them
popular in high latitudes, where freezing groundwater tends to
heave conventional piles out of the ground. Driving a screw pile is
quick and relatively quiet, and involves minimal vibration. There
is no need for
concrete and no spoil to get rid of, which represents a
considerable cost saving in remote locations.
Screw piles can be backed out of the ground just like undoing a
woodscrew, which makes them suitable for temporary installations.
They can also be used in tight spots where there simply isnt room
to drive a conventional pile. Long piles designed to be installed
in confined places can be assembled by joining multiple sections
together. According to Mr Coats, Globally, its a multi-billion
dollar market.
COMPARED WITH EXISTING TECHNOLOGY, THEY ARE EASIER AND
FASTER TO SET UP, WHICH DRAMATICALLY IMPROVES MANUFAC-TURING
EFFICIENCY.
S H A F T S K I N F R I C T I O N
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28 Engineering Insight Volume 15/6
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