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Re-contouring / Slope Reduction Costs

Model for Cost of Re-contouring

An Example from Reclamation Cost Service, Section RS Models

Re-contouring refers to one of a number of variations of the task of reducing slopes of a stockpile of waste, overburden, tailings, or an abandoned pit wall. These materials are often placed in a way that leaves their side-slopes at or near the angle of repose. The preferred way to reduce the side-slope angle of these stockpiles has a bulldozer excavating horizontal cuts into the materials and then casting it down the face of the stockpile. It repeats this process until all of the material along the face from the initial cut has been excavated, transported, and cast (Figure 1). After a point roughly half-way down the vertical extent of the stockpile, all of the additional material moved will consist of that previously excavated from above. As such, re-handling of previously cast material becomes part of the re-contouring process and represents about one-half of all material moved. Following is a hypothetical example. Cost are average US $ (2009).

Initial conditions at the site:
  • Stockpile height = 400 feet (122 m)
  • Stockpile slope = 42o (angle of repose)
  • Stockpile length along the mid-point of slope = 400 feet (122 m)
  • Final slope angle = 19o
  • Crawler tractor with blade, 850 horsepower
  • Unit costs assumed for model
    • Labor:
      • Foreman - $27.54/hour
      • Surveyor - $26.70/hour
      • Equipment operator - $23.33/hour
      • Mechanic - $22.66/hour
      • Laborer - $20.60/hour
      • Burden rate - 36.1% of wages
    • Equipment operation:
      • Diesel fuel $2.645/gallon ($0.699/liter)
      • Lubricants $8.09/gallon ($2.137/liter)

    Maintenance and repair parts, ground engaging components, and ownership costs are included in final cost. Almost all of the costs of re-contouring are attributable to either labor or to the expenses of owning and operating the machine. Few supplies are consumed.

    Estimated costs

    Estimated cost = $339,900 per 100 feet of length along slope (Table 12 from Model RS 1), for a length of 400 feet ... Final cost = $339,600 x 4 = $1,359,600

    Cost distribution of estimated final cost (given as a minimum percent of final cost)
  • Labor - 13%
  • Fuel - 22.3%
  • Equipment operating and ownership - 64.7%
  • Site work evaluation parameters (assumptions)
  • In-place density - 3,220 pounds/cubic yard
  • Loose density - 2,875 pounds/cubic yard
  • Compacted density - 3,220 pounds/cubic yard
  • Blade capacity - 45 cubic yards
  • Traction efficiency - 40% to 90%
  • Excavated cut thickness - 6 feet
  • Volumes excavated may vary by density, swell, and compaction characteristics of the material. Cost are heavily influenced by the efficiencies of the dozer-s blade and the dozer-s ability to gain and maintain traction.

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