Construction Operations and Methods (Depth)
Concepts
Equipment productivity is the core of depth questions: cycle time, bucket or blade capacity, fill factor, load factor, job efficiency, and unit conversions. Know excavators, loaders, dozers, scrapers, graders, compactors, trucks, and cranes; haul cycle and matching; dewatering; pile driving; concrete placement; and trenchless methods. Production is usually expressed in bank cubic yards per hour.
Traps
Using loose volume where bank volume is required; forgetting the fill factor; treating job efficiency as 60 min/hr when it is 45–50; mismatched truck and loader cycles; cycle time in seconds but production in hours. For cranes, use net capacity after deductions. For compaction, number of passes and lift thickness matter, not just drum weight.
Worked example
An excavator has a 1.5-cy bucket, fill factor 0.90, cycle time 30 s, and job efficiency 50 min/hr. Production = 1.5 × 0.90 × (3,600/30) × (50/60) = 1.35 × 120 × 0.833 ≈ 135 lcy/hr. With 25% swell, bank production = 135/1.25 = 108 bcy/hr. To move 10,000 bcy, allow about 93 working hours before downtime.
Rule of thumb
Match haul units so the loader waits no more than about one bucket cycle; 4–6 passes to fill a truck is common. Dozer production falls with push distance; beyond about 100 ft, consider a scraper or excavator-truck combination.