Modern Quarrying Q4 2019

“Roads should be three times the width of the widest truck, so tyres aren’t bumping into the safety berms or dropping into ditches” KENT CLIFTON

scuffing and wear on the treads. In addition, superelevation allows trucks to operate at more consistent speeds, which means less braking and less heat – another cause of shortened tyre and component life. The amount of superelevation depends on the curve’s radius and the speed at which it is negotiated. Because superelevated turns can prevent a danger when slippery, those over 10% should be used with caution. Another approach to superelevated curves is to determine the safe speed for negotiating a turn at a certain lateral tyre force. In general, a 20% lateral coefficient of traction is safe for all but slippery conditions. Grade is also important because it affects where the load sits on the tyres. The goal is for 33% of the load to be in the front of the truck and

66% to be in the rear, Clifton says. The ideal grade is between 8 and 10% with low rolling resistance of 2% or less. It’s also important to remember that the haul road begins at the loading face and ends at the dump point. Proper design of bench and dump areas can increase tyre life as well by reducing spillage that can become a hazard to tyres. Trucks should be able to quickly come in, turn around, and then back up. “You don’t want to turn the steering wheel and move the tyres while the truck is not in motion because when tyres twist on top of the rocks, it causes wear,” Clifton says. Road width is another concern. “Roads should be three times the width of the widest truck, so tyres aren’t bumping into the safety berms or dropping into ditches,” he says. Using the proper material to prepare and maintain the road bed is also important. If the surface under the haul road is soft or moist, rolling resistance is high and tyres are allowed to sink – which means contact with dirt along the sidewall. This can wear away the rubber from the tyres. Usually in cases of high rolling resistance, the ground is wet – another threat to tyre life. “Moisture causes tyres to slip. And when tyres slip, they are not

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QUARTER 4 - 2019 MODERN QUARRYING