A contractor has been invited to submit a tender for the removal of waste from an open cut mine, at 2 million BCM per year. The contractor utilises the following equipment:
• Caterpillar 992K Front End Loaders (13.68 tonne payload); and
• Komatsu HD785-5 Rear Dump Trucks (99.0 tonne payload).

In bidding for the waste removal contract, the contractor must determine how many trucks and loaders are required to meet the production target and the cost of production. The contractor is also unsure whether to continue with the same equipment or upgrade to larger equipment.

The productivity results are to be reported by volume rather than weight. Since we are working in metric units, this will mean that productivities are expressed as bcm/op.hour, bcm/shift and bcm/year.




The waste has an insitu bank density of 2.2 tonnes/cu.metre. The material swell factors are used to convert bank volumes to loose volumes in the loader bucket and the truck tray. Note that both swell factors are based on insitu volume. The swell factors for the waste the contractor is to move are as follows:




Swell Factor - Insitu to Loader Bucket 1.20

Swell Factor - Insitu to Truck Tray 1.25




For the contractor's loaders mining waste, set the loader bucket fill factor to average. This should equate to a factor of 0.72 on a heaped basis (0.87 on a struck basis) for a Front End Loader.




The contractor operates on two shifts per day, from Monday to Friday. In addition, there is one over-time shift on Saturdays. The only rostered days of the year that are not worked are Christmas Day and Good Friday. The contractor annually allows for ten shifts lost due to industrial action and ten shifts lost as a result of wet weather. Each shift is ten hours long. The following delays occur within each shift:




Crib break 30 minutes operating

Delays either side of crib 2 x 5 minutes operating

Delay at start of shift 5 minutes non-operating

Delay at end of shift 5 minutes operating

Delays for blasting 5 minutes non-operating

Clean-up around loader 15 minutes operating

Refuelling is carried out outside normal production hours.




The contractor's 992 loaders have an expected mechanical availability of 90% and each loader pass takes 35 seconds.




The capital cost to the contractor of a 992G loader is $400,000. The contractor bases its cash flow on a 10% salvage value at the end of the loader life of 25,000 hours or 5 years (whichever occurs first). The loaders are depreciated at a rate of 15% on a straight line basis.




This operating cost consists of the following components:




Operating Labour $54.76/op.hr

Maintenance Labour $19.52/op.hr

Liquid Fuels $25.26/op.hr

Lube $3.79/op.hr

Tyre Replacement $11.01/op.hr

Wear Items $6.00/op.hr

Repair Parts $45.00/op.hr

Major Overhaul $18.00/op.hr







The contractor's trucks are equipped with standard motors and are designed to carry the manufacturer's rated payload. The Komatsu HD785-5 trucks have an availability of 85%.




Operational studies show a spot time at the loader is 24 seconds, dump spot time is 20 seconds and a dump time of 30 seconds.




The truck capital cost is $200,000. A 10% salvage value at the end of the truck life of 30,000 hours or 6 years is assumed. The trucks depreciate at 25% on a straight-line basis.




This operating cost consists of the following components:




Operating Labour $46.37/op.hr

Maintenance Labour $18.24/op.hr

Liquid Fuels $17.24/op.hr

Lube $2.59/op.hr

Tyre Replacement $10.91/op.hr

Wear Items $4.30/op.hr

Repair Parts $24.08/op.hr

Major Overhaul $10.75/op.hr




Figure 1 shows a typical haul profile on which the waste contract is based. Conditions to be expected in the mine are listed below:

• Within 50 metres of the shovel and dump point, the truck speed is restricted to 30 km/hr;
• Around corners, trucks should not exceed 30 km/hr.; and
• When travelling down ramps, trucks must not exceed 40 km/hr.



The haul profile in figure 1 is representative of haul routes at the mid-life of the waste contract. In the early years the pit is shallower and in the later years it is deeper. The change in RL and the length of the ramp out of the pit vary as follows:



The distance and elevation from the surface to the top of the waste dump do not change. In planning we need to understand how the productivity requirements change for the life of the contract.




The contractor wishes to investigate the cost benefits of moving to larger equipment for the waste removal contract. The details of the larger equipment items in which the contractor is interested are as follows:




With this equipment, each loader pass takes 30 seconds. Also for the trucks, the spot time at the loader is 30 seconds. The spot time at the dump is 30 seconds and the dump time is 30 seconds.




Detailing any assumptions made, please address the questions:




What is the Loose Density in the loader bucket?

What are the total annual working hours for the loader?

What is the total fleet operating shifts for the year?

What is the total operating cost per hour?

What is the total operating cost per hour for the truck?

What is the optimum fleet size?

Which equipment fleet would you recommend the contractor purchase?


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Top of Bench = 270 R 150m => Haul Route Pit Floor Year 1 2 3 4 5 Length of Pit Ramp 200 metres 300 metres 400 metres 500 metres 600 metres Item Name Type Capacity Availability Capital Salvage Value Life in Years Life in Hours Depreciation type Depreciation Rate Total Operating Cost Shovel Komatsu Demag H 285 S Hydraulic Shovel 16.0 cu.m heaped 90% $2,000,000 10% 8 35000 Straight line 15% $222.73 Truck Dresser 510E Rear Dump Trucks 136.14 tonne payload 85% $1,300,000 10% 8 35000 Straight line 25% $163.50