Click on the picture for a closer look.
Click on the picture for a closer look.
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Civil engineering contractor Earney Contracts,
based just outside Lisburn, Northern Ireland is
making cost savings on water pipeline trenching
projects with its Schaeff WS-60 excavator mounted
milling cutter attachment. The company has also
found the WS-60 Cutting Unit to be more versatile,
efficient, faster, considerably quieter, less
disruptive to traffic and local residents and
more environmentally acceptable than traditional
trenching with noisy vibrating breakers.
Earney Contracts has been specialising in pipeline
trenching principally with breakers. However,
the company had been looking for alternative trenching
equipment more suited to projects in hard and
rocky ground. A visit to the Schaeff stand at
the 2002 SED plant show in England by one of the
founder's sons Andrew Earney produced a successful
end to the search. The Schaeff WS-60 Cutting unit
seemed the ideal choice so the company hired it
from Schaeff for two weeks to evaluate its suitability
and performance on a hard rock trenching project
at Crossgar, County Down.
"It was a big success trenching in the hard
rock and we were very pleased with its performance,"
says Andrew Earney. "It cut a 4 m deep trench
850 mm wide and straight down without any over
break and we reused the excavated spoil, pulverised
by the Schaeff milling cutter, as backfill. The
trench would have been about 4m wide at the top
if we had dug and broken it out in the normal
way with a breaker. The Schaeff Cutting Unit was
also considerably quieter than the breaker, with
the added bonus of no vibration. Vibration monitoring
tests carried out at houses next to the trenching
produced readings of 0.02 mm/s for the WS-60 compared
to 7.5 mm/s for the breaker."
The trial was so successful Earney Contracts bought
the WS-60 specifically for another nearby approximate
£0.45 M contract to lay 7.2 km of 350 mm
diameter mains water pipe in a 1.5 m deep, 900
mm wide trench. The steel pipeline is for a link
main being laid down the centre of the Ballynahinch
to Crossgar road for the Valley Partnership, a
joint venture between contractor Farrans and Water
Services.
Earney Contracts mounted the WS-60 Cutting Unit
on a quick hitch attachment, which is fitted on
the company's 20 t Cat 320BL hydraulic excavator
in place of the host machine's standard bucket.
The WS-60 Cutting Unit is pushed through the asphalt
road surface and into the underlying hard, shaley
Winstone rock. The rotating cutter is simply moved
back and forth along the trench line, gradually
increasing depth down to the required 1.5 m penetration.
The WS-60 accurately forms a straight sided, flat-bottomed
trench and after pulverising the material to full
depth, a second smaller excavator follows on digging
out the graded spoil. The 5.5 m long sections
of pipe are placed on a 50 mm thick bedding of
12 mm aggregate, which is also used as an initial
100 mm covering, prior to the pulverised spoil
being placed back on top as backfill. The recycled
material is compacted and the trench completed
with new asphalt base and wearing course for a
return to traffic. Earney Contracts has peaked
at 125 m/day of completed pipe and reinstated
road, but average production is about 70 m/day,
equivalent to an average 110 m3/day of excavated
spoil with the WS-60 Cutting Unit. A set of 56
Kennametal picks on the WS-60 lasts around two
weeks in the Winstone, corresponding to a wear
rate of just under 20 m3/pick.
"The WS-60 is more versatile, quicker and
simpler to use than a breaker and has enabled
us to make major savings on our trenching
operation," says Andrew Earney. "The
Schaeff cutter produces a Type 1 backfill, is
very accurate, and allows us to trim, if necessary,
to produce a very neat, tidy, flat and level bottomed,
straight sided trench. If we had used a breaker
we would have had to have taken out twice as much
material, which we couldn't then reuse, with the
consequential added disruption and cost of carting
it away and replacing with new backfill. The WS-60's
milling operation also leaves a jagged and uneven
edge to the asphalt at the top of the trench,
which provides a much better and stronger bond
with the new asphalt overlay than the clean saw
cut edges produced with conventional trenching.
So the Schaeff WS-60 is very environmentally acceptable
and we have also it used to form manholes and
trenches for house foundations."
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