24-MMP-A5 Surface Mining Methods and Design · December 2018
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
Reference texts: Hustrulid, Kuchta & Martin, Open Pit Mine Planning and Design (3rd ed.) — truck-shovel match factor, dragline stripping geometry, capital cost indexes, open-pit scheduling; SME Mining Engineering Handbook (3rd ed.) — equipment costing, mine dewatering, cost-index escalation.
Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.
Availability and utilization. In an 8760-hour calendar year, mechanical availability is the fraction of scheduled operating time a machine is mechanically fit to run: MA = (Scheduled hours − Downtime for repair/maintenance) / Scheduled hours. Utilization is the fraction of AVAILABLE time the machine is actually productively used: U = Operating hours / Available hours. The two multiply to give overall effectiveness: Overall = MA × U × (Scheduled hours / 8760).
Making the numbers look better. Both ratios can be flattered by changing the DENOMINATOR rather than improving real performance: reporting “scheduled” or “operating” availability (excluding planned shutdowns, standby, weather and blast-clearance delays from the base) instead of “calendar” or “physical” availability (based on the full 8760 h) inflates the percentage without changing a single wrench-turn of maintenance performance. Similarly, quoting utilization against “available” hours rather than against total SCHEDULED or calendar hours hides genuine idle/standby time. A reader must always ask “available (or scheduled) OF WHAT base” before comparing two sites’ percentages.
Which ‘hours’ for replacement. Replacement decisions should be based on Smh (Service Meter Hours) — actual operating hours accumulated on the machine’s own hour-meter (engine-on productive hours), not calendar age or mileage, because component wear (engine, transmission, hydraulics, undercarriage) is driven by hours of real work, not elapsed calendar time. Typical mobile open-pit equipment life: large haul trucks 50,000–80,000 h (structure)/ 12,000–20,000 h between major engine rebuilds; hydraulic/rope shovels 80,000–120,000 h; blast-hole rotary drills 40,000–60,000 h; dozers/graders 20,000–30,000 h — all far short of the roughly 87,600 h an 8760 h/yr × 10 yr calendar span would imply, confirming why hour-based (not calendar-based) replacement is standard.
| Item | Answer |
|---|---|
| Mechanical availability | (Scheduled − downtime)/Scheduled |
| Utilization | Operating hours/Available hours |
| Flattering trick | shrink the denominator base (scheduled/available instead of calendar/physical) |
| Replacement basis | Service Meter Hours (SMH), not calendar age |
| Typical life | trucks 50,000–80,000 h; shovels 80,000–120,000 h; drills 40,000–60,000 h; dozers 20,000–30,000 h |
