Haul roads are the major arteries of any mining operation. They are of extreme importance in productivity of the mine and health of the mining fleet. There are complex elements that need specific care when designing haul roads. If this process goes wrong then you’re going have more problems than you need. The design of a haul road is not an easy task, read our conversation with mining design principle – Roger Thompson. It requires careful consideration for both safety concerns as well as efficiency. Haul roads cost millions of dollars per kilometre to build. Hence systematic design and implementation of the roads is important. Poor construction of haul roads causes liabilities. It impacts productivity, safety and wear and tear of vehicles. 

Global Road Technology gives you 10 haul road terms you must know: 

  • rolling resistance 
  • haul truck productivity
  • trolley-assist 
  • load transmission 
  • surface mining haulage health 
  • payload balance 
  • cyclic deterioration rate
  • tyre wear 
  • haul roads 
  • tyre life 

Rolling resistance (RR)

It’s the force resisting a vehicle’s tires as they roll across a surface. Tyre roughness and pressure, strength, surface roughness and deformation contribute to RR. Poor haul roads increase the resistive force working against vehicle motion. Hence more fuel consumption. This increases the risk of haul truck wear and tear and the knock-on effect of loss in productivity of the mine. Reduction in RR enables the mine site to save on operational costs. 

Haul truck productivity 

Refers to the production capacity of haul truck units per hour. Haul truck productivity and auxiliary equipment effective use correlate. Effective use of auxiliary equipment prolongs maintenance cycles of key segments haul roads. Haul truck productivity ensues as truck speeds increase due to better rolling resistance. Low costs in highest producing companies in open pit mining have one thing in common, the best haul roads. 

Trolley-assist 

Trolley-assist haul truck is a configuration that allows electrical supply to the propel motors of haul trucks. The electric grid of the mine engages the truck on the trolley lines. This is a great advance to reduce emissions. Benefits include lower maintenance ramps and fatigue impacts on the hauler. It doubles the speed when connected to the trolley, compared to when running on diesel. There are cost savings associated to fuel consumptions. There is a large reduction on CO2 emissions.

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Load transmission

Loads transmitted from haul trucks to mine roads via the tyres. There aren’t restricted to loaded weight (GVW) of the haulage fleet. Tyres succumb to varying loads. There are the load balance in the haul truck body, ground conditions and haul truck motions by both. The outcomes are much higher loads between the tyre and ground. This results in faster road deterioration rates. It increases rolling resistance and lowers road and hauler productivity. This also results in higher fuel consumption and lower tire life. 

Surface mining haulage health

It is all about assuring the availability and productivity of haulage systems. It’s achieved through taking a wholistic view from the running surface up. It’s about establishing measurable improvement indicating metrics for haul roads, tyres and emissions. That impacts haul truck availability and productivity. This results in greater control over the $/ton operational and maintenance costs. 

Payload balance 

Payload balance plays an important role in haul truck reliability. Unbalanced loading leads to excessive fatigue of structure, components and tires. It is one important factor in lessening haul truck roll, pitch and rack motions. The latter is proportional to haul truck frame fatigue and increased repair times. It lowers availability payloads with different angles of repose. Different broken rock density creates wide front to rear axle payload distributions. That more than anything impact the loading and life of tires. Loadscan mining payload scanner provides visibility and automated alerts. These can be on underloading, overloading and off centre loading. It offers 3D profiles of all scanned loads. This drives compliance of safe/effective loading practices. That allows allocated training where required and done by whom is best to provide it. 

Cyclic deterioration rate 

The rate of increase in rolling resistance. Its important to understand cyclic deterioration rate (CDR) of haul surfaces. Under tire to ground in-motion loading levels, that are 25% to 50% higher than one sixth of the GVW per tire. Like body load placement, CDR is controllable from road design onwards. Knowing CDR is important for planned operation tons-per-day ratings over the road life.

Tyre wear

Overloading and spillage of materials creates debris on the haul roads. These have an impact on tyre wear. It creates more risk of incidental premature tyre failure. Reducing tyre wear requires best practice in good haul road construction and surfacing. Smooth gradient transitions are also important. Cleaning loose rocks and spillage from the roads, dumps and at the face also helps deal with tyre wear. 

Haul roads 

Roads designed for heavy or bulk transfer of materials by haul trucks in the mining industry. In most cases there are permanent (40%) and non-permanent haul roads (60%). These make up the haul road network on most surface mining operations. It is worth the effort to put in the best haul roads you can. This gives savings in cycle times, ground engagement wear, hydraulics, haul road dust control, ponding. Haul road bearing capacity changes with increasing loading haul truck round trip cycles. Adverse haul truck motions from imbalanced loads cause faster road deterioration. While poor road quality causes haul truck adverse motions. The result equals lower tire life and lower haul truck availability. So higher fuel use and emissions and greater maintenance costs.

Tyre life 

Grading haul roads to their operational tyre life promotes reduction of cut opportunities. Consistent grading reduces rolling resistance and tkph (tonne kilometre per hour). This increases tyre life. It is important to create a tyre life curve for your mining operation. This enables you to device strategies to increase tyre life. Higher RR can play havoc with wheel group life. A 1% increase in RR can reduce wheel group life by approx. 25%. 3% increase in RR will reduce the wheel group life by over 50%. 

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