Functional design
&
sheeting material selection

Most surface mine operators agree good roads are desirable, but find it difficult to translate this requirement into an effective and responsive surfacing (sheeting or wearing course) material selection.

An overview of the wearing course material selection for mine haul road applications is discussed, together with appropriate wearing course material selection guidelines. Using material performance models, a typical application is presented.

Download zipped files, extract to same folder and open spreadsheet in Excel.

Road performance and rolling resistance can be estimated from a qualitative visual evaluation of the key 'defects' influencing road condition are identified.

For each road defect, the product of defect degree (how bad) (measured on a scale of 1-5) and extent (how much) (measured on a scale of 1-5) are scored for each of these defects. The sum of the individual defect scores (degree x extent) gives the overall defect score which can be related to rolling resistance and functionality of the road.

The spreadsheet prompts for defect scoring based on visual examples of each defect and degree, then determines the rolling resistance representing the overall condition of the road.

Download and open spreadsheet in Excel.

Rolling resistance relates primarily to the key defects of potholes, corrugations, rutting, loose material and stoniness in or on the road. Using the rating system described above, the rolling resistance is determined by rating the key defects.

Repeating this process at regular intervals enables a deterioration rate to be determined and road maintenance (grading) scheduled at a point where rolling resistance becomes excessive (and the 'value' generated by reducing rolling resistance exceeds the 'cost' of the road maintenance activity itself.

More details can be found under 'Road Maintenance Management'.

Download and open spreadsheet in Excel.

Rolling resistance at any point in time can also be determined for each haul road based on the sheeting material key parameters of

• PI (plasticity Index),
  
• CBR (California Bearing Ratio 4-day soak),
  
• SP (shrinkage product) and
  
• GC (grading coefficient).
  

When coupled with traffic volume (kt hauled per day) and truck speed, the rolling resistance progression can be estimated.

Rolling resistance progression is important in determining how your road sheeting responds to increasing truck traffic - and the basis for truck performance and productivity estimations.