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Maintaining haul roads key to cost saving

The factors that need to be considered to ensure a safe and cost-effective haulage route include grades, drainage and road width design.
?As a starting point, it?s important to em-phasise that haul road maintenance requires a dedicated focus and must be addressed on a continual basis as part of the operation cycle since good roads improve production, extend tyre life and reduce overall operating costs. The reverse scenario is equally true,? explained Mark Senyard, whose team specialises in conducting production studies for Barloword Equipment clients. Barloworld Equipment is the exclusive Caterpillar distributor in southern Africa.

Tyres are a key expenditure item to be preserved for as long as possible. However, approximately 80 per cent of all large tyres fail before wear due to poor maintenance and operating practices. This statistic is underscored by a recent study at a world-class metal mine which indicated cut (45 per cent) and impact (20 per cent) as the largest contributing factors towards premature tyre failure.

The chief culprit is spillage from off-highway haul trucks. It is therefore critical that a motor grader is deployed on-site to maintain haulage routes and remove loose debris.

Poor road maintenance practices also result in an increase in rolling resistance (the pressure exerted on the tyres by a road?s riding surface). For off-highway trucks running radial-ply tyres, one would typically expect a minimum rolling resistance of 1.2 per cent for a hard and well-maintained permanent haul road. However, if this figure increases by just five per cent, the impact becomes disproportionately greater and could result in a 10 per cent decrease in production, and a 35 per cent increase in production costs.

There are three key factors that determine optimum haul road condition: material quality, design and maintenance. It is equally important that haul roads begin at the loading face and end at the dump, and maintaining good floor conditions in both areas will definitely lower tyre wear and fuel burn costs.

?Once a road deteriorates, it takes five times as long to repair it again to an acceptable condition. In this respect, it is important in terms of maintenance to match the right grader and water tanker units to suit the quarry?s haulage route,? Mark said.

GRADER SIZE
The size of the grader will depend primarily on the width of the haul road, but also be influenced by the road?s construction, and the quarry?s ongoing maintenance programme. A neglected road will require more intensive remedial action, and a larger grader to cut and grade final levels.

Caterpillar?s H-Series motor graders have set the industry standard across the quarrying,mining and construction sectors for many years, and have now been complemented by the introduction of the M-Series, which is gaining ground in southern Africa following its global introduction. Available in seven different models, the M-Series starts with the 120M (14,093kg operating weight), and extends to the imposing 24M (62,456kg operating weight). The first 24M unit sold in South Africa is currently working at Isibonelo Colliery in Mpumalanga.
What distinguishes the M-Series from the H-Series is the introduction of joystick controls, replacing the conventional steering wheel and operating levers. The two electro-hydraulic joysticks reduce hand and wrist movement by up to 78 per cent compared to conventional lever controls, greatly enhancing operating efficiency, while exceptional visibility (view forward to the blade, working surface and front tyres) make the M-Series easier to operate without sacrificing control.

?For reshaping haul roads, the typical blade loads are about one-third to half of full capacity,? Mark Senyard explained. ?However, where large hauling units travel on softer materials, heavy blade loads may be required to reshape the road surface. Many quarriesare also located in mountainous areas, requiring haul roads with steep grades or where very precise roadway elevations and slopes are desired. These considerations will determine which grader model best suits the application.?

The 120M through 16M (26,060 kg operatingweight) models provide a broad range of extended blade positions beneficial for mid-range bank sloping, ditch cutting and ditch cleaning. A long wheel base allows for an aggressive blade angle, permitting material to flow more freely and reducing power requirements.

Servicing time and cost on the M-Series hasalso been lowered. For example, top accessibledrawbar wear inserts and the shimless mouldboard retention system make DCM (Drawbar, Circle and Mouldboard) adjustmentsfast and simple, delivering precise material control while lowering operating costs.

DUST SUPPRESSION
Of equal importance to having a well-constructed and graded haul road is the needfor dust suppression. Dust thrown up by continuous haulage can reduce visibility and mobility, posing a safety hazard. Additionally, regular watering helps to maintain compaction.
?As a guideline, the size of the water tanker should match the side of the haul trucks,? Mark suggested. ?For example, if the quarry is using Cat 777 units, then these should be supported by Cat 777 water trucks. Tanker size will also depend on factors such as the length of the haul road and the number of fill points along the route. ?Spot? watering also works well for areas with limited water supply,and for safe travel, a ?checkerboard? or ?spot? intermittent pattern is recommended to reduce the slippage risk during retarding on grades.
?Also consider the downside of over-watering, as washing out the fines will lower the cohesion properties of the road, accelerating deterioration and causing potholes to form. The latter will grow rapidly if ignored, and soft and wet spots need to be completely refilled and compacted with good, dry material.?

Optimally, the slope of the road should adequately carry away storm water run-off, with evidence of minimal water entry into the road sub-base.

In addition to designing haul roads to save on costs, safety is of paramount importance. To avoid the risks of collisions on two-way sections, the design should cater for worst-case scenarios with approaching corners and crests clearly visible at standard travel speeds. The short distance for horizontal and vertical curves must be sufficient for a machine to stop before reaching a hazard or obstacle, and the distance from the operator?s eye must equal or exceed the required stopping distances.
?Remember to keep grades smooth and constant as this minimises transmission shifts, maintains a higher average speed, and enables more constant braking effort on returns,? Mark Senyard recommended. Grades of less than 10 per cent are recommended for maximum tyre life.

Computing the haul road width on horizontal curves is a specialist area. For example, a wider road is required on curves to account for the overhang occurring at the front and rear of the machine, as well as the lateral clearance between passing trucks.
?On one-way straights and corners, a minimum of two to 2.5 truck widths is recommended,? Mark said. ?For two-way traffic, this would increase to a minimum of three to 3.5 truck widths on the straights, and a minimum of 3.5 to four truck widths in the corners. Each quarry is different and an extra width allowance should be made where needed, to accommodate difficult driving conditions.? ?

Mark Senyard is the product manager of Barloworld Equipment, South Africa.
This article is reproduced with the kind permission of Modern Quarrying, the official magazine of the Institute of Quarrying Southern Africa

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