Surface mining haulage accounts for up to 50% of total open-pit operating expenses, with off-the-road (OTR) tires and diesel fuel constituting primary operational expenditures. Heavy haul trucks operating under gross vehicle weights exceeding 400 tons place immense physical stress on mine haul roads. Sub-optimal roadway conditions accelerate premature tire failure modes, including sharp cuts, impact fractures, tread chunking, and thermal separation. Poor road geometry and high surface roughness also elevate rolling resistance, forcing severe engine lugging and excessive fuel consumption. Standardized road engineering directly reduces tire wear rates, lowers fuel burn, improves truck cycle times, and enhances overall site safety.
The geometric design of the roadway controls the momentum of the vehicles, distribution of axle loads, and lateral and longitudinal forces acting on heavy haul vehicles. The maximum longitudinal grade should be kept to an 8%-10% slope, while the desired constant grade should be approximately 8%-9.2%. Steep slopes require engines to function in low gear ratios, which in turn increases fuel usage and heat generation in drive tires. Constant grades eliminate the need for gear changes and rapid transfer of load from one axle set to another. In two lane haul roads, the minimum recommended width of the road should be three and a half to four times the truck width to reduce lateral scrubbing. Banked curves help overcome centrifugal force effects and ensure even distribution of load among the inside and outside tires.
The demand on tractive effort is dictated by rolling resistance within the wearing course. Dense and compact surfaces have a reference rolling resistance between 1.5% and 2.0%. However, flexible subgrades allow tire penetration resulting in the constant climb of heavy vehicles out of rut hollows. The tire penetration of 50 mm will raise the rolling resistance up to 5.0%, and the penetration of 100 mm will raise the value to 8.0%. For each 1% increase in rolling resistance, there is a corresponding increase in fleet fuel consumption by 2% to 3%. Abrasive rocks and impact fractures constitute 74% of all tire failures.
Course maintenance is imperative to counteract structural weakening on the roads exposed to excessive stress through high cyclic load wheel movement on them. Moisture affects road base, leading to rutting, infiltration of dirt into the subgrade, and road deterioration. Excess surface water makes sharp stone spillage invisible, making it impossible for the operator to identify potential dangers. The process of proper drainage involves creating cross-slope crown between 2% and 4%, roadside ditches, and clean culverts. A special set of equipment, including graders, wheel dozers, and water trucks, helps even out ruts and clear off spilled stones on operating haul roads. Cleanup of spillage near the loader shovel area and dumping area helps to get rid of any sharp penetrators, thus preserving tire casing integrity.
Haul roads are valuable production tools affecting the bottom line as well as longevity in surface mining operations. Effective engineering design turns traffic lanes into efficient, low-rolling-resistance channels. Mild slopes of 8%-10% avoid extreme load stresses and minimize tire wear due to excessive heat generation. Wearing surfaces kept in good repair allow for a rolling resistance level approaching 2%, saving as much as 19% on diesel fuel costs and protecting from virtually all cuts in tire casing. Grading and quick elimination of spillages, combined with adequate cross slope drainage, safeguard subbases and tire cases. Haul road evaluations can assist in accomplishing prompt cost savings and increasing productivity.
