## Friday, January 20, 2012

### How Much Dirt, How Fast, How Far, Part III

This week I have been overseeing the fleet of tractors that are moving dirt around on the vacant lots below the Excel Math offices. I've also been investigating the types of elementary math skills that tractor drivers might need.

Here are the pull-push pair, shown coming up on a "road grader" who is not actually in front of them, but on a similar path downhill about 100 feet away.

HOW MUCH WORK?
In the past two blogs I've provided some of the data related to the tractors, and how the contractor can determine how long it will take to move the earth. Where do the charts and raw data come from? From the manufacturer, Caterpillar. They decided how large the tractors could be, how much power was necessary, how much soil could be moved, how fast the tractors can go and how much fuel they burn, etc.

Let's assume
•  they can move 40,000 lbs (each) for each cycle or 40 yards of soil
•  a cycle takes 3 minutes
•  a pair can do 17 cycles per hour
•  they work 9 hours a day including overtime
That means they can move 80,000 x 17 x 9 = 12,240,000 pounds of earth or 80 x 17 x 9 = 12,240 yards per day!

If we wanted to, we could take the area of the lot (shown yesterday) and calculate the days required to move the soil. But we don't want to do all that work, do we? Besides, I can just watch and calculate from observation. Here's a view from the bottom of the slope as they head back uphill, empty.

HOW MUCH MONEY?
While engineers were designing tractors and measuring their earth-moving capacity, accountants were determining how much money the tractors consume - including original cost, the depreciation, maintenance, spare parts, tires, fuel, insurance and other items. They decide how many average hours a tractor will last - in this case 17,000 hours. Dividing the operating lifetime and the total cost adds up to at least \$80-100 per hour per tractor (plus tax and operator salaries). That means the lifetime total spent on each of these monsters is at least \$1,360,000.

Using Caterpillar's numbers, the push me-pull you team will cost our contractor about \$1500 per day plus cost of the operators.

Would you like to see them in action? I thought so. I walked down and spent a few minutes filming the tag-team operation.

PS: The original pushmi-pullyu from Doctor Doolittle did not move dirt (yes, I read all his books and still have many of them).