The following paper is a general description of haul roads found within a typical overseas [tropical] quarrying environment. As the examples are all overseas, they take no recognition of UK legislation, whether applicable or not. A lack of suitable haul roads can lead to the situation shown in figure one where a fully loaded Cat 769 dump truck was driven off the side of a narrow road. The road was the exact width of the vehicle and passed through a residential area, luckily, the driver was unharmed. The next day, another driver (also unharmed) did exactly the same thing, in the same place and almost destroyed a house, proving the point that for some company's, lessons are learned the hard way.
This paper defines the quarry as the place from where the stone is won, not the process area, unless they are one and the same place. Quarry haul roads can generally be categorised under one or more of the following headings;
Each of the above will have its own
design priority and criteria, time and
effort spent in design will always
save money later on, unfortunately
the regime of cash flow found when
developing a quarry often calls for
minimum expenditure at the outset.
Although useful at the start, cost
cutting in design usually cost much
more later on when the road has to
be moved. The use of modern
surveying equipment and dedicated
computer design packages enables
a quarry to be designed at the
planning stage and the design
carried through until the resource is
exhausted and the site closed. It is
much more cost effective to design the road with planning software than it is to keep
physically removing and rebuilding it. At this time, the planner can place the road in the
quarry, view rapid changes of direction or other route changes for optimum arc of
visibility and measure gradients. The design should consider inclines, whereby the
maximum slope value should be not more than 1 in12, however in areas where this is
not attainable, the road must be designed to enable a gradient no steeper than 1 in 10
to be achieved, and this, only to be used by suitable vehicles operating within their
design criteria. The bends should be near horizontal and well drained. At design stage
it should be remembered that bends and acute changes in gradient cause the trucks to
brake and accelerate, both these actions waste energy, both increasing operating costs
and causing environmental damage with excessive noise and fuel smoke.
The road with the least design
requirement will be the access
track, this may only be a path
dozed over or through the
overburden. Its life may only
extend to the full 
development
of the benches, at which time,
a more permanent road would
be constructed. The design
should be sufficiently detailed
to facilitate an upgrade as
required. Even though this
road will only be used on
occasion, it should generally
comply with the requirements
of the main haul roads, both in
design and construction, particularly with regard to safety and the environment. If it is
only to be used by tracked vehicles, the management may mitigate the costs of design
and construction by accepting a lower standard of surfacing, drainage, width and slope
values, all providing that the track conforms to local legislation and remains safe to use.
The road shown in figure three displays extreme slope values, blind corners and
complete lack of drainage, these factors caused many accidents.
This road should preferably,
be designed at the preliminary
stages of quarry planning, and
if possible it should provide
access to every area of the
developing quarry. Usually
this is achieved by
constructing the road at one
end of the benches, from
which each bench is
developed. As this is to be a
semi permanent road, more
time and funding should be
made available at design and
construction to get it right first
time. Constantly repositioning
and repairing the road is
costly and can confuse the drivers. This road is likely to require the greatest slope
values as it extends to serve all of the benches. To accommodate changes in the quarry
or mitigate the slope values the road may be designed with looping and "switchbacks"
or it may travel alternately across each of the benches. Figure four shows a well
designed bench road being used by a Cat 777 dump truck, the road is more than wide
enough to accept three times the width of the largest vehicle that uses it, and the driver
has a wide arc of vision. The bend or switchback has been cut to be horizontal, dust
suppression has been provided by a water spray.
This is the main artery
between the quarry production
area and the process plant. In
the UK this may be one and
the same area, however. In
larger quarries or open pit
mines the haul route may
extend several kilometres. As
this road is likely to be in
existence for the whole life of
the project it is wise to design
and construct it to a high
standard. At initial design
stage, maximum efforts
should be made to ensure that the road will have a minimal environmental impact, both
during construction and use. In Jamaica and other Caribbean countries the maximum
footprint of the quarry is restricted, and the whole length of the haul road is considered
as being part of the quarry. It is often forgotten that the surface area of a haul road can
often be larger than that of the benches and quarrying area. Figure five shows a main
haul road used by Cat 769 dump trucks feeding limestone to a kiln in Zambia, although
well designed, the road is suffering from a lack of maintenance with the drains becoming
filled and overgrowth. It is interesting to note that at this site the main slope into the
quarry was sealed with concrete, making the surface all weather and reducing tyre wear.
It is not always possible to
design a road to theoretical
perfection with moderate
inclines and bends having a
zero gradient. The
responsibility for design and
construction of the road
shown in figure six was given
to the writer following the
death of the quarry manager
during initial construction. Due
to the requirement to climb
two hundred metres in one
thousand, the task was at first
considered to be impossible,
eventually a road design and
constructed that had four switchbacks. The road was used without serious incident by
Cat 250 articulated dumpers, the fact that there was not a serious accident was due
more to the quality of the drivers than the design. Constructing roads as shown with high
gradients and acute bends is not recommended.
This section does not intend to constitute a working plan of construction but is intended as a guide to the general layout of haul roads.
The road should be constructed to a standard, probably comparable with a heavy duty highway and its construction should follow conventional techniques. The foundation upon which the road is constructed is of significant importance.
If the road is following a
reasonably level terrain, then
for drainage purposes it must
be elevated. In this instance
construction would begin with
an excavation to either
suitably solid ground (sub
formation) or if this is found to
be plastic (clay), then a
surface membrane and
unbound fill material would be
used to ensure a suitable
bearing ratio was achieved.
Further construction of
compacted fills would be layed
with the final surface being
sealed. Although as is often
the case, solid rock is not
considered as a suitable surface for a haul road, this is because of difficulty in achieving
the correct contour, its lack of draining ability and general poor grip due to polishing.
Also, a clean rock surface can in some instances provide a slip plane between itself and
the rock fill, this may cause the road to fail at points of high lateral force. The interface
could possibly allow water to pass, this would ultimately wash away the fines in the fill,
reduce the compaction by introducing voids and ultimately destabilise the construction.
Generally, it is much better to blast the rock, cut to profile, build with suitable fill and
compact. The sub surfacing should be compacted to a value suitable for the projected
dynamic loading, which are especially severe during braking.
Depending on the duty required from the road it may be necessary to seal the surface, this can be a graded surfacing of roadstone, concrete, asphalt, or "chip and spray". Sealing the road will prevent the ingress of water, aid drainage, reduce drag and therefore improve fuel consumption, reduce noise and dust.
Building a road without drains is pointless, water entering the road will cause the fill material to effectively loose specific gravity (being suspended by the water), will lubricate the fill material thereby reducing friction and enabling it to become displaced under load, will wash away the fines, thereby leaving voids and will wash away the surface material.
Unsealed roads are often designed to have a super-elevation or cross fall, (meaning the
surface will always fall in one direction at any particular location, the fall will be in the
direction of the highest terrain (see figure eight). It is important for the surface water to
remain as sheet flow (not turbulent), to accomplish this, calculations must be made for
the expected maximum rainfall and the slope value of the surface designed accordingly.
A typical slope value will be about 2 to 5% anything greater will not only make the water
to flow too fast, but will cause excessive tyre wear and side loading on the wheel
bearings of the dump trucks.
From the super-elevation the
water will discharge into a
longitudinal drain, possible
using a membrane to prevent
erosion. The drains must be
designed with full
consideration given to the
maximum flow requirements
and where required, geo-
textiles and armour rock can
be used to stabilise and
strengthen the channel, the
geo-textiles may need to be
installed to prevent water from
entering the road fill. A flow
velocity of 1 m/s is the
maximum rate suggested to control erosion in earthen drains, this is a maximum rate
and for easily erodible soils the velocity should be reduced by the use of rock dams and
slopes of less than 3%. The drain will terminate at a constructed culvert and usually a
cross drain will carry the water beneath the road to a reinforced drop structure for
dispersal. The cross drain should have sufficient diameter to allow cleaning (minimum
800 mm) and the drop structure will be designed to prevent erosion.
Designing a road with a super-elevation has the added advantages of ease of maintenance by a grader (only one profile) and the truck always being directed by gravity away from the side of the road that has the drop.
Due to the constant volume of heavy traffic together with a relatively light, without maintenance a haul road will very quickly fail. Regardless of the surfacing, the road will require regular maintenance and repair.
The following maintenance activities are advised:
If the road is sealed using asphalt or chip and spray, then it is important to repair any holes that may develop, failure to carry out surface repairs will allow water to soak into the fill, destabilising the structure.
Measures for environmental
mitigation should
be
considered and implemented
at design stage. Much of the
environmental nuisance can
be mitigated by careful
design, such as constructing
as much of the road as is
possible beneath exposed
features, such as beneath the
rim of a valley or shielded
from sight by a hillside. The
road shown in Figure six was
constructed adjacent to the
islands airport and gave the
tourists their first view of the
island, the visual amenity
would have been improved by
tree planting had the volcano not destroyed the site. Figure ten shows the effect of
failing to put prevention measures into operation. In this instance, simply watering the
road would have reduced the dust.
The main environmental areas of concern are likely to be;
A full study of all the above impact should have been completed at design stage at measures of mitigation incorporated into the design.
The quarry is a heavily restricted area and the haul road whether or not it is in the quarry will be subject to local legislation, normally, the only personnel authorised to use the haul roads should be;
To ensure road safety, the following recommendations may be considered;
Where required, (which is
often the full length of the
carriageway) the road should
be fitted with substantial
ARMCO safety barriers. The
construction of berms often
causes the truck to overturn
and only the very largest
boulders will be sufficient to
prevent a truck from breaking
through. ARMCO will reduce
the impact and contain a
vehicle without causing
excessive additional damage.
The driver of the Cat 966
shown in Figure eleven was
out collecting firewood when he turned from the road, he survived without injury.
The Haul road can be
designed to place the
maximum distance between
dust production and sensitive
areas. These sensitive areas
can be protected by use of the
topography, either natural,
such as, woodland, or man
made with the careful
positioning of screens. The
travelling distance of dust can
be reduced by taking
advantage of the direction of
the prevailing wind and
building screens to reduce
wind velocity and if possible
disruption in the form of
vortices. Dust can be reduced
by using a hard rock surfacing
or preferably, coating the road with bitumen or asphalt, keeping haul routes as short as
possible and reducing gradients. In addition, haul routes to waste dumps and stockpiles
can be located in the lee of prevailing winds and away from sensitive locations, such as,
residential locations, and main highways. Leafy trees can be grown at the sides of the
road which will filter the air and trap the dust particles.
The technology is now available for a computer aided design to produce accurate noise modelling of site operations. The programme uses a three dimensional computer model of the topography and adjacent areas as a basis for undertaking automated noise calculations. The location of the haul routes together with details of noise prediction points are then added to the model. The contribution of noise from each item of plant and any haul routes, allowing for the attenuation of noise with distance and any noise reduction effects are then calculated for each point. These are then summarised to obtain the overall noise levels in terms of Leq.
The code of practice for basic information for noise control'. In particular, the following measures are commonly used;
Poor road maintenance or excessive use of "sleeping policemen" will not only cause damage to the vehicles but will create noise due to the trucks bouncing and the bodies slapping on the chassis.
The design, construction,
operation and maintenance of
haul roads may not be the
most exciting part of
quarrying, but they are vital to
the safety and smooth
operation of the business.
Time and money spent in
maintenance of the roads may
not always give an immediate
cash return, but cutting down
on the maintenance will soon
be converted into an increase
in the cost of maintaining the
trucks plus reduced
production. This paper
recommends that the roads
are designed to last, are well
constructed and maintained. If the roads cross public areas they will eventually either
be absorbed into the local road network (as happens in Jamaica) or be removed and the
land reassigned for other uses. Figure thirteen shows what can happen when it all goes
wrong, this driver using safe wide roads and after considerable training survived an
accident in a fully loaded truck that overturned at high speed.
Reference material; Jack Mills
A Technical Discussion of Mining Operations in the Lime and Cement Industries of Zambia and Malawi. A Doctoral thesis presented to The University of Nottingham.