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HaulRoadMaintenance

As a general rule, the ability to travelcomfortably along a quarry haulroad ina light commercial vehicle at a safe and

acceptablespeed is a good indication of a well-maintained surface. However, this is justone indication, and a host of otherfactors needto be considered to ensure a safe and cost-effective haulage route. These factors includegradients, drainage and road width design.

As a starting point, it is important toemphasize that haul road maintenancerequires a dedicated focus and must beaddressed on a continual basis as part of theoperational cycle since good roads improveproduction,extendtyre life and reduce overall

operating costs. The reverse scenario isequally true.Tyres are a key expenditure item to be

preserved for as long as possible. However,despite this, approximately 80% of all largetyres fail before weardue to poormaintenanceand operating practices. This statistic isunderscored by a recent study at a majormetal mine, which indicated tyre cuts (45%)and impact damage (20%) as the largestcontributing factors towards premature tyrefailure.

The chief culprit is spillage from off-highway haulage trucks. It is, therefore,critical that a motor-graderis deployedon siteto continually maintain haulage routes andremove loose debris.

Poor road maintenance practices alsoresult in an increase in rolling resistance,defined as the pressure exerted on the tyresby a roads riding surface. Typically, for off-

highway trucks running radial-ply tyres, aminimum rolling resistance of around 1.2%would be expected for a hard and well-maintained permanent haul road. However,if this figure increases by just 5%, the impactbecomes disproportionately greaterand couldresult in up to a 10%decrease in production,and a 35% increase in production costs.

Essentially, there are three key factors thatdetermine optimum haul road condition:material quality; design; and maintenance. Itis equally important to note that haul roadsbegin at the loading face and end at thedumping point, and maintaining good floorconditions in both of these areaswill definitely

reduced tyre wear and fuel burn costs.Once a road deteriorates, assuming it waswell constructed in the first place, it takes fivetimes as long to repair it again to anacceptable condition. In this respect, it isimportant, in terms of maintenance, to matchtheright grader andwater tanker units to thequarrys haulage route.

Grader sizeThe size of the grader will depend primarilyon the width of the haul road, but will also beinfluenced by the roads construction, and thequarrys ongoing maintenance programme. Aneglected road will require more intensiveremedial action and a larger grader to cut and

grade final levels.Caterpillars H-Series motor-graders have

set the industry standard across the quarrying,mining and construction sectors for manyyears, and have now been complemented by

the introduction of the M-Series, which isgaining ground in southern Africa following itsglobal introduction. Available in seven differentmodels, the M-Series starts with the 120M(14,093kg operating weight) and extends to the24 M (62,456kg operating weight).

What distinguishes the M-Series from theH-Series is the introduction of joystickcontrols, replacing the conventional steeringwheel and operating levers. The two electro-hydraulic joysticks reduce hand and wristmovement by as much as 78% compared withconventional lever controls, greatly enhancingoperating efficiency, while the high level ofvisibility (view forward to the blade, working

surface and front tyres) makes the M-Serieseasier to operate without sacrificing control.For reshaping haul roads, the typical blade

loads are about one-third to half of fullcapacity. However, where large hauling unitstravel on softer materials, heavy blade loadsmay be required to reshape the road surface.Many quarries are also located in areasrequiring haul roads with steep gradients orwhere very precise roadway elevations andslopes are desired. These considerationswill determine which grader model bestsuits the application.

The 120M through 16M (26,060kg operatingweight) models provide a broad range ofextended blade positions that are particularly

beneficial in mid-range bank sloping, ditchcutting and ditch cleaning. A long wheelbasepermits an aggressive blade angle, allowingmaterial to flow more freely and reducingpower requirements.

A vital factor in the value chain

By Mark Senyard, product manager of Barloworld Equipment, South Africa

September 2010 www.Agg-Net.com 17

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18 www.Agg-Net.com September 2010

Servicing time and cost on the M-Series hasalso been reduced. For example, topaccessible drawbar wear inserts and theshimless mouldboard retention system make

DCM (drawbar, circle and mouldboard)adjustments fast and simple, deliveringprecise material control while further reducingoperating costs.

Dust suppressionOf equal importance to having a well-constructed and graded haul road is theneed for dust suppression. Dust thrown up bycontinuous haulage can reduce visibility andmobility, posing a safety hazard. Additionally,regular watering helps to maintaincompaction.

As a guideline, the size of the water tanker

should match the size of the haul trucks. Forexample, if the quarry is using Cat 777 units,these should be supported by Cat 777 watertrucks. Tanker size will also depend on

factors such as the length of the haul road andthe location of fill points. Spot watering alsoworks well for areas with limited watersupply, and for safe travel, a checkerboardor intermittent spot pattern is recommendedto reduce the slippage risk during retardationon gradients.

The downside of over-watering shouldalso be considered, as washing out the fineswill lower the cohesive properties of theroad, accelerating deterioration and causingpotholes to form. These will grow rapidly ifignored, and soft and wet spots need to becompletely refilled and compacted with good,

dry material. Optimally, the slope of the roadshould adequately carry away storm waterrun-off, with minimal evidence of water entryinto the road sub-base.

In addition to designing haul roads to saveon costs, safety is of paramount importance.To avoid the risk of collisions on two-waysections, the design should cater for worst-case scenarios with approaching cornersand crests clearly visible at standard travelspeeds. The short distance for horizontal andvertical curves must be sufficient for amachine to stop before reaching a hazard orobstacle, and the distance from the operatorseye must equal or exceed the requiredstopping distances.

Gradients should be kept smooth andconstant as this minimizes transmissionshifts, permits a higher average speed to bemaintained, and allows more constant braking

effort on returns. Gradients of less than 10%are recommended for maximum tyre life.

Computing the haul road width onhorizontal curves is a specialist area. Forexample, a wider road is required on curvesto account for the overhang occurring at thefront and rear of the machine, as well as thelateral clearance between passing trucks.

On one-way straights and corners, aminimum of two to 2.5 truck widths isrecommended, but for two-way traffic, thiswould increase to a minimum of 3 to 3.5 truckwidths on the straights, and a minimum of 3.5to 4 truck widths on the corners. However,each quarry is different and extra width

allowance should be made where needed, toaccommodate difficult driving conditions.

This article first appeared in Modern

Quarrying, the official magazine of the Institute

of Quarrying Southern Africa.

Grades need to be kept smooth and constant, minimizing transmission shifts, maintaining a higher

average speed, and allowing more constant braking effort on returns

Haul road maintenance must be addressed continually as part of the operational cycle. Good roads improve production, extend tyre life and reduce overall

operating costs

Loading & Hauling