Question

A project has 300,000 BCY (wet excavated earth). We need to complete excavation in 12 weeks – Figure to work 6 days per week, 10 hours per day.

1. Backhoe Problem:

1. Find required production per hour in BCY/hr and LCY/hr.

2. Determine bucket Fill Factor

3. Calculate bucket cycles per hour

4. Calculate required bucket capacity assuming the following:

a. Work efficiency = 50 min/60 min hr

5. Select required excavator (Caterpillar)

6. Suggest suitable off-road haul truck for project. Assume 4 buckets to load a truck load.

Answer 1

solution:

given that, earth to be excavated = 300000 BCY

time available = 12 weeks (6 days working)

working time / day = 10 hours

1) production required / hour = excavating volume of earth / time available

= 300000 / (12 * 6 * 10)

= 416.67 BCY / hour

Assuming 25% swell, LCY = 1.25 BCY = 416.67 * 1.25 = 520.84 LYC

2) Assuming the bucket size of 1.75 cubic yards and it is filling only 1.70 cubic yards in each cycle.

therefore, bucket fill factor = (average fill in each cycle / full capacity of the bucket) 100

= (1.70 / 1.75) 100 = 97.14%

3) volume to be excavated per hour = 416.67 BCY

if only one backhoe is working then, the cycle length = volume to be excavated per hour/capacity of the bucket

= 416.67 / 1.70 = 245.1 = 245 (approx.) cycles per hour

4) If work efficiency is 50 min. per hour, the capacity of bucket required = [(total earth to be excavated / (week * working days in a week * working hours in the day)) / no. of cycles per hour]

according to 50 min. per hour, work per day will be only 8 hours and 20 minutes.

therefore, the new capacity of bucket = [(300000 / (12 * 6 * 8.33)) / 245]

= 2.0416 cubic yards