IM 2016 June 2016 | Page 55

HAUL ROADS_proof 25/05/2016 10:36 Page 6

HAUL ROADS
68.6 cm deep and 3.7 m wide in a single pass.
Miedecke says it can mill and crush in situ
material to produce a more consistent and ideal
particle size, as well as offer improved grading.
In haul road construction, the traditional
method is to import material to the road site. Due
to the scale of mining operations, the size of the
material is often larger than is desirable.
Miedecke says he often sees oversized material
in the critical 2 m layer below the surface, which
will lead to inconsistent compaction and
settlement that in turn results in high
maintenance and grading costs after construction.
“You’ve got very poor particle size distribution,
which leads to voids amongst all those rocks,” he
says. “The mining company will continue
building the road over that area, but as time goes
on, there will be settlement and differential
compaction, and then the road becomes undulated
and difficult to ride, difficult to grade. It can lose
drainage integrity. You’ll have ponds in low areas
of the road. It becomes a compounding problem.”
A fleet of equipment is necessary in this
traditional approach, including shovels or wheel
loaders and haul trucks to move material to the
road construction site, one or two large
bulldozers, one or two large graders, a water cart
and a compactor.
There are a lot of steps in this approach. Proof
Engineers has an 11-action process just for the
production of surface material. Once a road is

complete, maintenance is a major ongoing issue;
and dealing with water – drainage – is the top
priority.
Another maintenance item in both hard rock
and coal environments is spillage from trucks. A
lot of fine material falls out of trucks and gets run
over. When it gets wet, it can become slippery.
And then the mine loses time due to wet weather.
Also a factor is the growing size of haul trucks
and their payloads. The pitch and yaw
characteristics of the large trucks put more stress
on the road as a whole and deeper into the
substructure. Miedecke has seen trucks essentially
dig up material from 3 or 4 m below the surface
of seemingly well-constructed haul roads.
Typically, dozers are used to extract the large
rocks. Miedecke thought if that material could
be broken up and incorporated into the surface
materials, the road would be structurally
stronger. There are additional benefits when
the particle size distribution is improved in that
the dusty fine particles are held longer and the
road will require less water to maintain dust
levels. The Terrain Leveler SEM offered that
capability.
The machine has a cutting drum that operates
with a top-down motion, which allows the cutter
teeth to penetrate without using the machine’s
tractive effort to drive the teeth into the rock. As
the unit travels backwards and the drum rotates,
the teeth on top of the drum advance over the

top of the unbroken material surface. The
technique promotes greater operational
efficiency as more horsepower goes into cutting
rock and less into moving the machine.
In 2013 Proof Engineers was part of a rehab
project at a South African coal mine where more
than 60% of the haul roads were on coal
benches. Poor blasting controls and uneven
topography made those roads difficult to
construct and maintain. They had very slow haul
velocities and were rough and dirty.
Proof Engineers tried two ways to make the
road better. One used two bulldozers with rippers
to break the coal, and then the machines track
rolled the coal to crush the larger pieces. After
that a grader shaped the road. Finally, haul trucks
compacted the material. They improved the
quality of the road, but it was very resource- and
time-consuming.
The other method involved a Vermeer T1255III
Terrain Leveler SEM, which could mill the coal in
situ. It exceeded the productivity of the two large
bulldozers by a considerable degree, and the
particle size distribution was better and had less
oversized particles.
Truck travel speeds were about 50% higher
than both the traditional construction method
and the one using bulldozers. In this instance, it
also took less than half the time to grade and
shape the road with the SEM than it did with the
bulldozers. IM

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“W
’ only
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d as our last
l installation.”
i
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and electrowinning, we can make a difference.

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