Tony Cutler of Otraco International presents a case study from the Nimingarra mine site in Australia that examines the effect of good haul-road conditions on truck productivity and tyre workload

1. July / August 2013 www. .com
78 tyre management
In October 1985, Goldsworthy Mining,
which operated the Goldsworthy and
Shay Gap iron-ore mines in the
Pilbara region of Western Australia,
undertook a pilot ore-haulage pro-gramme
of 20,000t over a 45km cycle
from the Nimingarra pit to the Shay Gap
crusher using Wabco 110t haul trucks.
Two years later in November 1987,
routine production began from
Nimingarra. The ore was again hauled to
the Shay Gap crusher – however, this
time over a shorter, realigned haul road
(32km cycle) that eliminated most of the
dips and curves of the road used in
1985.
These hauls are among the longest
ever undertaken using rear-dump haul
trucks of 100t or greater capacity, and
therefore provide an excellent opportu-nity
to examine the effect of the improved
haul road conditions on haul-truck
productivity and tyre workload.
The effecTs of change
Improving the condition of a haul road
can result in a substantial improvement
in haul-truck productivity. It can also
reduce tyre workload considerably,
thereby reducing the incidence of
low-life tyre heat failures for mine sites
that are operating haul-truck tyres close
to their workload limit.
The work-shift average speed is
defined as the distance travelled by a
haul truck during a mine shift, divided by
the shift duration. For example, if a haul
truck covers a total of 120km in an
eight-hour shift, then its work-shift
average speed is 15km per hour.
Work-shift average speed is one of
the two determinants of tyre workload
or tonne kilometres per hour (TKPH); the
other is tyre average load. Generally,
work-shift average speed increases as
the haul-cycle distance increases. This is
because, on a longer haul, a truck
spends more time travelling relative to
its periods at rest while being loaded
and while dumping its load.
Let us look at two scenarios: scenario
one is a short haul where the work-shift
average speed for a haul truck with an
average payload of 100t operating on a
4km cycle is 12km/h. Scenario two is a
long haul. If that same truck were
operating on an 8km cycle, then its work
shift average speed would typically be
higher – in the order of 16km/h.
For the 4km haul cycle, the productiv-ity
of each haul truck is 2,400t during an
eight-hour shift (12k/h x 8hr / 4km x
100t), while for the 8km haul cycle,
productivity drops by 33% to 1,600t per
truck per shift (16k/h x 8hr / 8km x 100t).
Although the work-shift average
speed in scenario two is higher by
one-third, this has been more than offset
by a doubling of haulage distance,
causing an overall reduction in truck
productivity. We can therefore conclude
that a higher work-shift average speed is
typically associated with longer haul
distances, with a resultant increase in
tyre workload (operational TKPH) and a
reduction in haul-truck productivity.
UnexpecTed resUlTs
The 1985 pilot haulage at Nimingarra
was on a relatively poorly formed road
rules of the road
Tony Cutler of Otraco
International presents a case
study from the Nimingarra mine
site in Australia that examines
the effect of good haul-road
conditions on truck productivity
and tyre workload
Hauling at the
Collahuasi
copper mine
in Chile
“Improving
the
condition of
a haul road
can result in
a substan-tial
improve-ment
in
haul-truck
productivity”

2. 79
www. .com July / August 2013
tyre management
that followed the contours of the terrain
– rising, dipping and curving – between
the Nimingarra pit and the Shay Gap
crusher.
The road was extensively reworked
prior to the start of full production
haulage in 1987. Cut and fill was
undertaken to straighten the road and to
eliminate many rises and dips. This
realignment of the road shortened its
length from 22.5km to 16km – a
reduction of 29%.
As we have seen, shorter haul
distances generally result in a reduced
work shift average speed which:
• partially offsets the truck productivity
increase associated with the shorter
haul cycle, and
• reduces tyre workload (operational
TKPH).
However, what occurred at Nimingarra
was quite different and unexpected. The
highest work-shift average speed
recorded for the haul trucks operating at
Nimingarra in 1985 had been 22.5km/h
for four complete haulage cycles over an
eight-hour shift. The average shift speed
noted during the first month of
operation, November 1987, on the
realigned and shortened haul road was
24km/h, which allowed six complete
haulage cycles over an eight-hour shift.
Contrary to expectations, the shorter
haul cycle resulted in a higher work-shift
average speed, providing much higher
productivity than had been budgeted.
While the 29% reduction in haul
distance had been expected to result in
a 3% drop in work-shift average speed
– from 22.5km/h to 21.8km/h, it in fact
increased by 6% to 24km/h. Work-shift
average speed on the new shortened,
realigned road was 10% higher than
anticipated – with an equivalent 10%
increase in actual haul-truck productivity
compared with what had been
budgeted.
Managing Tyre workload
While the higher than expected
work-shift average speed on the
improved Nimingarra haul road
produced an equally unexpected
windfall in productivity, it immediately
set off alarm bells in relation to tyre
workload.
The longest haul in the Shay Gap mine
proper at the time was from Sunset 7 pit
to the crusher with a work shift average
speed of 20.6km/h. A heat study
conducted in March 1987 had shown
that tyre temperatures on this haul were
approaching maximum allowable levels.
So a work-shift average speed of 24km/h
on the new Nimingarra haul had the
potential to create a spate of expensive
(in terms of tyre usage cost and
tyre-related haul-truck downtime),
low-life tyre heat separation failures.
Otraco immediately recommended
that measures be implemented to
minimise the risk of tyre heat damage.
These included:
• tyre pressure and temperature
monitoring at the end of each haul
cycle, with maximum allowable limits
set for inflation pressure and
temperature build-up, and
• swapping trucks between Nimingarra
and the shorter Shay Gap hauls as
required.
While high tyre air-chamber tempera-tures
and inflation pressure build-ups
were recorded over the duration of
Nimingarra haulage from November
1987 – regular chamber temperatures of
90ºC and as much as 100ºC, and
pressure build-ups of 30psi (2.07bar) and
occasionally considerably higher – the
incidence of heat-related tyre failures
was exceptionally low.
Based on theoretical TKPH calcula-tions,
the operational TKPH, at a
work-shift average speed of 24km/h,
exceeded the tyre manufacturers’ TKPH
ratings by between 10% and 15%. The
tyres used on this haul should have been
suffering an exceedingly high incidence
of low-life heat-separation damage.
However, they were not, even when the
trucks were on occasion left operating
on the long Nimingarra haul rather than
being swapped to shorter Shay Gap
hauls.
This highlights a major shortcoming of
the TKPH system of calculating tyre
workload in that it does not take into
account haul-road condition.
Inhospitable
conditions and
dusty road
surfaces can
cause heavy
wear on truck
tyres
“While the
higher than
expected
work-shift
average
speed
on the
improved
Nimingarra
haul road
produced a
windfall in
productivity,
it set off
alarm bells
in relation
to tyre
workload”
Truck tyres
sustain a heavy
workload on long
mine haul routes

3. July / August 2013 www. .com
82 tyre management
Lessons Learnt
The lesson from haulage at Nimingarra is
that improved haul-road conditions can
lead to a substantial increase in a haul
truck’s productivity while simultaneously
reducing the workload of its tyres.
There are four main elements to
making haul roads more productive and
tyre-friendly. They are:
1. Reducing haul distance and unneces-sary
gradients, through:
• horizontal curve minimisation; and
• vertical curve minimisation.
2. Recucing rolling resistance and
tyre/truck stress, through:
• pothole and undulation elimination;
• road sub-base material selection and
compaction; and
• selection of appropriate road surface
material and smoothing.
3. Reducing tyre/truck lateral stress,
through:
• road curve radius optimisation;
• road elevation optimisation; and
Improving the
conditions and
layout of mine
haul roads can
make a positive
contribution to
tyre efficiency
Maintaining the condition
of haul-truck tyres is critical
to the safe and efficient
operation of mines
• road camber minimisation and
camber profile optimisation.
4. Reducing haulage bottlenecks,
through:
• road width optimisation.
The improvement in haul-road
conditions at Nimingarra between the
1985 pilot haulage programme and
1987 production haulage – and the
significant benefits gained in terms of
truck productivity and tyre workload –
were achieved mainly through the first
of these elements (reducing unnecessary
curves).
However, all four elements were
incorporated into the upgraded
Nimingarra haul road, and they all
contributed to improved productivity and
the ability of tyres to sustain an
operational TKPH that significantly
exceeded their TKPH rating. Apart from
productivity and tyre workload capability,
overall tyre life and truck component life
will also benefit substantially from
improved haul-road conditions.
“Overall
tyre life
and truck
component
life will also
benefit
substan-tially
from
improved
haul-road
conditions”