DESIGN ASSIGNMENT
Truck Cycle time and productivity
A limestone Quarry is being exploited for the refurbishing of an existing hydroelectric dam. The construction site is located 3.6 miles away from quarry. The first 1.1 miles near the quarry are on a 12% graded slope (down towards the quarry). The remaining 2.5 miles are on a flat surface.
Consider:
- Bulk material density of 2700 lb/yd3
- A spotting time of 12 seconds
- A bucket load (fill + raise + turn + dump + turn again, i.e. 1 loading pass) of 28 seconds
- Truck Utility is 85%
- Truck Availability is 80%
- Truck Workers Efficiency is 55 minutes per hour
- Truck turn and dump time is 25 seconds
- 2-8 hours shift per day
You are asked to design a new truck fleet for this operation. Production requirement is 40,000 short tons per day of material hauled to the construction site. Your local Caterpillar manufacturer informs you that four types of trucks are currently available in limited quantities:
- 9 – CAT 770G Flat Floor
- 5 – CAT 775E Quarry Flat Floor
- 10 – CAT 777D Dual Slope
- 2 – CAT 793D
The two loader type available (6 in stock) have a bucket of 12 cubic yards or 23,000 lb (assume a fill factor of 90%). You can select a second type of loader of your choice (max. quantity 6) from the CAT handbook.
Use the following assumptions:
- Retardation and rim-pull charts are the same for CAT 770G, CAT 777D and CAT 775E trucks. However, use caterpillar handbook for data if you plan to use CAT 793D truck.
- The Loader workers are energetic and work 60 minutes an hour with availability and utilization at 100% for loaders.
- Acceleration and deceleration can be neglected for this design
- During fall and spring season, because of rain, the road condition becomes like loose gravel. During winter season, the road condition becomes like packed snow. During summer season, the road condition becomes packed gravel.
- The dam work site cannot receive more than 42,000 short tons of material per day.
- Maximum allowed speed between the two work site is 45 mph
- Loading time is same for both types of loaders.
In order to design the fleet, the project director asks you to provide 3 situations alternatives, to assert potential sharp increase or decrease of the loader costs before the start of the project.
- Minimum waiting time for the fleet (Match Factor as close to 1 as possible)
- Over trucking (queuing)
- Under Trucking (loaders are waiting)
Bonus question (5 marks) : Optimize the fleet and come up with the most feasible design. Also provide environmental assessment.
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