A hydraulic excavator has a bucket capacity of 1.5 cubic meters. The cycle time for excavation including loading is 30 seconds. If the job requires moving 10,000 cubic meters of soil with a swell factor of 1.25, then what is the total time required (in hours) assuming 90% efficiency?
- A84.5 hours
- B77.2 hoursCorrect
- C92.6 hours
- D102.4 hours
Solution
Concept
Time for excavation
Formula
Output = bucket × cycles/h × efficiency
Step-by-step solution
1. Cycles per hour = 3600/30 = 120. 2. Output = 120 × 1.5 × 0.9 = 162 m³/h (loose). 3. Loose volume = 10 000 × 1.25 = 12 500 m³. 4. Time = 12 500 / 162 = 77.2 h.
Explanation
The soil swells on excavation, so the volume to be handled is greater than the bank volume.
Why the other options are wrong
84.5, 92.6 and 102.4 hours do not follow from 12 500/162.
Shortcut
Time = bank × swell ÷ (bucket × cycles × efficiency).
Common mistake
Ignoring the swell factor.
Correct answer: B) 77.2 hours