HAUL ROADS_proof 25/05/2016 10:41 Page 1
HAUL ROADS
Talking trafficability
Paul Moore interviewed one of the
leading global experts on mine haul roads
on recent developments as well as
reviewed some advice and offerings from
key OEMs and consultancies
ecognised as a leading global expert in
mine haul roads, Roger Thompson,
Professor of Mining Engineering at Curtin
University’s WA School of Mines told IM: “Truck
based haulage right now enjoys a 'fortunate
combination of unfortunate circumstances.'
Diesel fuel prices are lower than they have been
for several years – but so too are commodity
prices; the industry tyre shortage has eased for
most sites and ultra-truck tyre sizes – but the
growth in ultra-truck class shipments and
overall population has eased too, being
replaced and offset to a degree by increased
demand for smaller capacity haul trucks. So
overall, although the cost pressures on haulage
may have eased in quantum, in the balance, the
pressure is still on – in this case driven by the
lower commodity returns being achieved.
Fundamentally, the metrics also remain the
same, improving performance and driving down
costs – but increasingly this analysis is being
informed by 'big data' and the development of
abilities to analyse that data to spot emerging
issues with the haul road design, be it geometry,
structure, function or maintenance-driven.”
The higher resolution this data offers is being
used to evaluate what appear to be relatively
minor adjustments to, for instance, a haul
circuit, by optimising junction layouts, obviating
the need for stops or speed reductions in some
circuits. “Similarly with gear shifts or wheel
motor speeds, modifying a haul circuit both in
terms of geometry, layout and traffic
management planning to minimise unwarranted
and avoidable speed changes will generate
improvements in haul cycle times, reduced fuel
burn and truck drive system wear from engines,
through transmissions to tyres and the road
surface itself.”
Allied to these incremental modifications, are
R
48 International Mining | JUNE 2016
the broader objectives of delivering a 24/7
trafficable haul road. “Haul road trafficability is
typically assessed both terms of immediate
measures of performance – rolling resistance
and also longer-term measures which capture
the resilience of the road, both under dry and
wet weather conditions, up-time and remobilisation delays, frequency of re-sheeting,
etc. However, the factors that differentiate a
resilient road from a more vulnerable road are
poorly defined. There is a need to improve the
overall performance of the haul road system,
including construction materials selection,
design and construction practice, road
maintenance management and circuit
prioritisation through costed and targeted
improvements to both dry and wet weather
resilience and trafficability and re-mobilisation
delays, either associated with on-road
maintenance requirements, or due to roads
becoming unsafe to operate when wet.”
Rainfall and haul road downtime
Downtime associated with poor resilience of
mine haul roads varies inter-site, and also intrasite too, where various materials are used for
road sheeting, derived generally from a low-cost
and accessible (but not necessarily ideal, in
terms of required material specification) borrowpit source on-site. Thompson states: “What is
clear, however, is the rapid degradati on that
some road sheeting materials can undergo
when subjected to light rainfall, which causes a
haulage operation to either apply restrictive
speed limits, in the best case scenario, or stop
haulage entirely in the worst-case scenario,
when conditions become unsafe to haul and
road damage would accumulate.”
This has been observed in practice by
RoadSafety Training Services (RSTS) in
Water spraying a haul road on a dry day at
a coal mine in Indonesia to minimise dust,
however, most of the time in this part of
the world, wet conditions are the
challenge to trafficability not a solution
Australia, which has shown how small amounts
of rainfall (often less than 1 mm/m2 or 1
litre/m2) can significantly reduce trafficability
(represented as a loss of longitudinal friction)
and result in road surface conditions that
warrant road closure until the surface dries
back. “However, what specifically contributes to
this loss of trafficability or in contrast, offers
resilience to rainfall, is poorly understood.
Generic guidelines exist for the selection of a
haul road sheeting material, but do not extend
to identifying the specific material
characteristics that enhance, or diminish,
trafficability under wet or dry conditions.”
Using selected rainfall records from Western
Australia for example, there is an increasing
prevalence of low intensity (1-5 mm) rainfall
events over the period 1985 to date in many of
the Australian states’ key mining resource
centres. “If RSTS’s data is interpreted in the
context of the WA climate trends, then surface
mine haulage operations are either suspended
or speed restricted, for between 21 and 68 days
per annum and the trend would indicate the
frequency of these events will increase along
with anticipated climate changes. A mine in the
adjacent state of South Australia reports that on
average some 370 operating hours per year are
lost to wet weather haul road downtime and
subsequent delays for each truck and shovel in
their load and haulage fleet, which equates to
480,000 BCMs per excavator per year in lost
productivity. Historically, the mine has had on
average four times the predicted annual average
rainfall, and lost time due to these wet-weather
events averages 3.25 h/mm rainfall and can
exceed 12 h/mm in some instances.”
Whilst an all-weather haul road can be built
(usually sealed, stabilised and/or treated), mine
truck ultra-heavy wheel loads, coupled with the