Question

(20 points) A D8T crawler D8H crawler tractor with a universal blade is to be used in a slot-dozing operation. The material is dry, non-cohesive silty sand and is to be moved a distance of 250 ft from the beginning of the cut. Dozing is uphill on 4% grade. The operator will have average skill, the tractor will have a power-shift transmission, and both visibility and traction are assumed to be satisfactory. The material weighs 110 pcf in the bank state and is estimated to swell 14% in the loose state. Job efficiency is assumed to be equivalent to a 45-min hour. Assume that the owning and operating (O & O) cost for the tractor is $45.50 per hour and the operator's wage is $12.70 per hour. Calculate the direct cost of the proposed earth-moving operation in dollars per bcy.

Answer 1

Hi,

Solution as follows:

1. Assumptions:

Since the datasheet is not available with the question, we are making below assumptions in order to estimate the cost:

1. Max Speed – Forward = 6.6 mph
2. Operating Speed on the project (Average skill operator and 4% uphill) = 80% of the max speed = 5.28 mph
3. Max speed – Reverse = 8.8 mph
4. Blade Capacity ­– 11.4 yd³
5. Operating weight = 87400 lbs
6. Time for ramp up = 6 seconds
7. Time for maneuver = 3 seconds

2. Conversion of Bank Volume to Loose Volume:

Swell factor = 14%

1 BCY (Bank cubic yards) = 1.14 LCY (Loose cubic yards)

3. Check for carrying capacity by weight:

Loose capacity = 11.4 yd³

Bank Capacity = 11.4/1.14 = 10 yd³

Soil density = 110 pcf

Soil Weight = 10 x 110 x 27 = 29700 lbs

Since the weight of soil is less than the operating weight, it can carry 10 BCY (11.4 LCY) of earth.

4. Calculation of time required for each trip:

Average Distance = 250 ft

Forward Speed = 5.28 mph = 5.28 x 1.4667 = 7.744 ft / sec

Reverse Speed = 8.8 mph = 8.8 x 1.4667 = 12.907 ft / sec

Forward time = 250/7.744 = 32.28 sec

Reverse time = 250/12.907 =19.37 sec

Time for ramp up = 6 seconds

Time for maneuver = 3 seconds

Total time for one trip = 32.28 + 19.37 + 6 +3 = 60.65 seconds

5. Calculation of BCY Moved in one hour:

Job efficiency = 45 min per hour

Time required for one trip = 60.65 seconds

45 x 60 No.of trips in one hour = 60.65 = 44.518 trips

BCY moved in one hour = 44.518 x 10 = 445.18 BCY per hour

6. Calculation of BCY per hour Cost:

Tractor cost per hour = $45.50

Operator cost per hour = $12.70

Total Cost per hour = $45.50 + $12.70 = $58.20 per hour

58.20 Cost of earth moving (S/BCY) = 245,18 = $0.131 per BCY

Hope the solution provided above is clear. In case of any clarifications, please leave comment in comments section.

Please give us a good rating, if you are satisfied with the response.

How would you rate our reply?

Keep Chegging

Best Regards

Chegg Expert Team