Mining & Construction: Equipment Productivity and Cycle Economics
BEML's mining and construction line includes hydraulic excavators, bulldozers, dumpers and drills. The exam tests the production arithmetic behind fleet sizing: cycle time, bucket fill factor, swell factor, and matching loading units to haulers.
Core rules
- Loose volume = bucket capacity × bucket fill factor.
- Swell factor converts bank (in-situ) volume to loose: bank = loose ÷ swell factor. State which basis your data uses before calculating.
- Productivity: cycles per hour = 3600 ÷ cycle time in seconds, then multiply by job efficiency (productive minutes per 60).
- Pass matching: passes = hauler capacity ÷ (bucket capacity × fill factor), rounded up. A partial extra pass wastes a full cycle.
- Dozer output depends on blade volume, push distance and soil type; rippability is judged from seismic velocity.
Worked example
A 2.0 m³ excavator with fill factor 0.9, a 30 s cycle, 50 productive minutes per hour, loading a dumper of 12 m³ loose capacity. Cycles/hour = 3600 ÷ 30 = 120; with efficiency = 120 × 50/60 = 100 cycles/hour. Loose output = 2.0 × 0.9 × 100 = 180 lcm/hour. With swell factor 1.25, bank output = 180 ÷ 1.25 = 144 bcm/hour. Passes per truck = 12 ÷ (2.0 × 0.9) = 6.67 → 7 passes. The seventh pass only partly fills the body, so a 10–11 m³ body gives a cleaner match.
Traps that cost marks
- Reporting loose m³ as if it were bank m³, or multiplying by swell instead of dividing.
- Using struck bucket capacity without a fill factor for sticky clay or blasted rock.
- Assuming cycle time is only digging time; it includes swing, dump and repositioning.
- Matching trucks on struck volume rather than heaped or loose capacity.