MAINTENANCE
mines. This usually entails regular grading
and spraying or wetting of the haul road
surface. Dust suppression chemicals
consist of surfactants and binding agents
that are diluted into water to overcome the
natural hydrophobic characteristics of dust
particles, resulting in full wetting. Truck
tip and crusher areas are considered for
short term application of dust suppressant
and is surfactant bases. Stockpile feeding
and multiple transfer areas are considered
medium term application areas and a
binding agent is added, which under
normal circumstances will remain effective
for up to two weeks. Encrusting agents
are added to the mixture for areas of
long-term single application and can under
normal conditions have a life of up to three
months before re-application is needed.
Vista Training, a US-based company,
has identified the main causes of mine
trackless vehicle tyre damage. They found
that most commonly sidewall damage
resulted in tyre failure and it happens
when trucks and earthmoving equipment
move too close to berms and high bank
faces. This is more common on narrow
haul roads where trucks operators steer to
the outside edge of the haul road to pass
trucks each other and corners the second
most often.
The other identified incident areas
are associated with loading at a shovel
or tipping point, where backing up over
spilled material or backing up too far until
the truck's rear duals are resting upon the
edge of the pit face.
Trackless mine vehicles that run on a
rutted road is noted as another hazard as it
can cut the sidewall and put stress on the
carcass when entering and leaving the rut.
A rut will cause the tyre to wear unevenly
due to surface variations, reducing the
life of the tyre. As a remedial measure,
trackless fleet operators should be
encouraged to use different areas within
the haul lane to avoid creating or enlarging
ruts as far as possible.
Tyre pressure
Tyres need to be inflated to the correct
pressure for the terrain in which it is
operating. Underinflated tyres experience
significant sidewall deflection, especially
when the truck is travelling with a load.
The result is higher tread wear, stress in
tread and plies, weakened bonding and
increased heat build-up. Proper inflation
ensures maximum ground contact area,
optimum sidewall flexibility and reduced
heat levels of the tyre. Overinflated tyres
on the other hand can loosen traction as
the shape of the tyre becomes deformed,
decreasing the contact footprint area. The
overinflated tyres are also more prone to
damage, as stiffer tyres do not react to
road features.
Washboard profiles (corrugated road
surfaces) on sections of a haul road
create a bouncing motion if the vehicle
operator is driving over it at high speed.
These conditions affect the sidewalls of
the truck's tyres. Too much bouncing may
cause tyres to momentarily leave the
Travelling downhill laden with a full load increases the load on the front axle, generally
by the value of the gradient.
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MARCH 2020
road surface, amplifying sidewall flexing.
Damage from excessive flexing is not
immediately noticeable but is cumulative
and can be hard to spot in the early
stages. Excessive speed during cornering
has a similar effect. The best remedial
action is to grade the haul road to retain a
smooth operating surface.
Maintaining the road
Haul vehicle operators should avoid
running over any material that has spilled
onto the haul road. The best short-term
course of action is to safely manoeuvre
around the material until it can be safely
removed. The road maintenance crew
should be informed of the spillage either
by the operator responsible for the spillage
or the first operator to encounter it. The
edge of a concrete bumper block at the
mine's dump pit or load-out area can be
a severe tyre hazard and haul vehicle
operators should try to avoid making
direct contact with it. When backing up to
a bumper block or crusher, the operators
need to take care that no spillage occurs
in the pocket. Backing over spilled material
or sitting on top of it while dumping a load
will place excessive stress on the tyres.
Windrows, the long line of material
heaped created by normal grader road
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