Plant Equipment and Hire March 2020 | Page 27

MAINTENANCE grade for a mine haul road is between 8 and 10% with low rolling resistance of 2% or less. Travelling downhill laden with a full load increases the load on the front axle, generally by the value of the gradient. A cambered haul road or banked curves will increase the load carried by the tyres on one side of the haul vehicle. Most vehicles are wide and need a lot of space, both to drive and turn. Anyone that has ever been stuck behind an abnormal load transport, would have noted that mining vehicles may take up the equivalent of two lanes. Haul roads in quarries should ideally be three times the width of the widest haul vehicle, to prevent tyres from bumping into or scraping along the safety berms or drop into ditches. The design of bench and dump areas can increase tyre life and also reduce transportation spillage. The turn should be designed to be broad enough to enable to turn the equipment quickly without dry steering on loose material. Dry steering refers to the act of turning the steering wheel of a vehicle while it is stationary. This puts strain on the rack, pinion, pump, tie rods and bearings. It especially causes undue wear on the front steer wheels. Best material to build haul roads The material used to build the quarry haul roads should be fines materials that can be compacted. The fines are generally derived from waste material produced either during the crushing and screening of quarried material, or from the processing plant where ore is crushed and milled. Haul roads are built with various layers and different size material. It should be ensured that the rock materials used in the top layer are not over-sized or sharp. The material should also be packed down and compacted correctly to prevent undulations developing. It is therefore prudent to use a studded compaction roller prior to using the smooth vibrating roller to produce the final surface. The material should not become too moist when wet, to the extent where wheels sink into the haul road, bringing the sidewalls of the tyre in contact with dirt and wears away the rubber. Lime is usually added to permanent haul roads to stabilise clayey or very fine-grained material. If there is high rolling resistance on the haul road, the tyres are not biting into the road and in effect are burning rubber off the tyre. Environmental considerations Dust control is also required as part of the Environmental Management Plan at all www.equipmentandhire.co.za The profile of the haul roads, such as length, width, camber and elevation of curves and gradients has a considerable effect on dynamic overloading and on tyre scrub. The grade of the road is one of the first features that can be physically felt by the driver. The material used to build quarry haul roads should be fines materials that can be compacted. MARCH 2020 25