Mining in focus
Good haul roads at an opencast mine will extend
the life of the equipment’s tyres significantly.
Good roads prolong tyre life
One of the biggest operational expenses of running an equipment fleet on an
opencast mine, is both damage to and the replacement of tyres. Haul road design
and maintenance are key in keeping costs down, writes Nicolaas C Steenkamp.
T
he average life of a tyre for
equipment on an opencast mine
is 9 000 hours of operation but
can be significantly reduced due to haul
road conditions. The main causes of
damage to vehicle tyres are related to poor
haul road maintenance. Pete Holman,
senior consultant at Caterpillar Global
Mining, says that about 80% of all large
tyres fail before they wear out. “Cuts are
responsible for about 45% of failures, with
impacts causing nearly 30%,” he says.
The best haul roads have crowned
straight sections, super-elevated curves,
safety berms, and drainage ditches on
both sides. The design of the haul road
also influences the life of vehicle tyres.
The profile of the haul roads, such as
length, width, camber, and elevation of
curves and gradients, has a considerable
effect on dynamic overloading and on
tyre scrub. Well-designed haul roads also
increase fuel efficiency and operator safety.
Keep roads level
Super-elevation is the difference in height
between the inner and the outer edges
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of the bed of a banked road. Properly
designed super-elevation keeps loads level
and square on the tyres, decreasing side
forces on the tyre casing and reducing
scuffing and wear on the treads. It
also allows trucks to operate at more
consistent speeds, which means less
braking and less heat.
Grade is also important, because it
affects where the load sits on the tyres.
The ideal load distribution is for 33%
of the load to be in the front of the
truck and 66% to be in the rear. The
ideal grade for a haul road is between
eight and 10 degrees, with low rolling
resistance of two degrees or less.
Travelling downhill laden with a full
load increases the load on the front axle,
generally by the value of the gradient.
A cambered haul road or banked curves
will increase the load carried by the tyres
on one side of the machine.
Haul roads should ideally be three
times the width of the widest truck so
tyres do not bump into the safety berms
or drop into ditches. The design of bench
and dump areas can increase tyre life
and reduce spillage. The turn should
be broad enough to enable the quick
turning of equipment without dry
steering on loose material.
The material used to build haul
roads should be fines materials that
can be compacted. Haul roads are built
with various layers and different size
material. It should be ensured that the
rock materials used are not over-sized
or sharp. The material should also be
packed down and compacted correctly
to prevent undulations from developing.
The material should however not
become too moist when wet, to the
extent where wheels sink into the haul
road, bringing the sidewalls of the tyre
in contact with dirt, wearing away the
rubber. If there is high rolling resistance
on the haul road, the tyres are not biting
into the road and, in effect, are burning
rubber off the tyre. Dust control is also
required as part of the environmental
management plan at quarries. This
usually entails regular grading and
spraying or wetting of the haul road
surface.
FEBRUARY 2019 MINING MIRROR [33]