Matching An Excavator to Our Trucks

1. Matching An Excavator to Our Trucks ©2009 Dr. B. C. Paul Note – These Slides contain tables and information found in the Caterpillar Performance Handbook.

2. Backhoes and Excavators • Backhoe is a digging arm and bucket attached to the back of a machine • An Excavator puts the shovel on the front but has pivots on booms on the arm to make it dig below itself as opposed to above itself like a hydraulic front shovel

3. The 5230ME It can load a truck up To 32 feet high It can dig down up To 31 feet – that will Do a 30 foot high bench

4. Cat 777 Loading Height 14 feet 3 inches << 32 feet

5. The Heap Effect 9 feet at a 3:1 slope will create a heap 3 feet higher than the edge of the truck Ideal load can Dump the bucket Onto a pile Between 17 and 18 feet high Still easy for a 32 foot Dump height How high is this center Truck Bed Cross Section 18 ft 2 inches

6. Sizing a Bucket That is Reasonable for the Material A Rock Bucket Holds 21 cubic yards heaped

7. Fill Factors • The fact that a bucket geometry will heap to 21 cubic yards does not guarantee it will fill in the field • Easy Load stockpile 1 to 1.1 • Average 0.95 to 1 • Rather Difficult 0.9 to 0.95 • Difficult 0.85 to 0.9 • Digging down on an intact face is rather difficult • May get about 90 to 95% of rated • About 92% is 19.4 cubic yards

8. Need to Fill in a Reasonable Number of Passes • If you fill a truck with less than 3 passes you can’t get the load distributed – you’ll kill the suspension system • If you take too many passes to fill the truck will spend a large part of its cycle time sitting to be loaded. • Guidelines exist as to what tends to be workable • Cable Shovels (3 to 4 passes) • Hydraulic Shovels (4 or 5 passes) • FEL (4 to 6 passes) • Backhoes (often 5 to 7 passes)

9. Cat 769 (Our Little Truck) Load Capacity is 31.7 cubic yards and 82,533 lbs

10. But Which Is Limiting? • A Truck can be Weight or Volume Limited • Which depends on the material • Ours is Oil Shale

11. Material Weights Tables Exist in Many Handbooks This one is from the Caterpillar Performance Handbook

12. A Material Caution • In place rock is a solid with only internal air spaces and pores • For loading and hauling rock tends to break into chunks that have air spaces between them • If you’ve ever tried to put dirt back in a hole after digging it out you know what “Swell” means

13. Always Distinguish Between Bank and Loose Volume The difference between bank and loose weight is huge Saw some students foul up homework by looking on the internet And grabbing a weight number with no idea what it was. Many Internet numbers are bank weights since loose weights are often Important only in mine planning.

14. In Our Case We Are Given the Loose Weight • 2107 lbs per cubic yard • 31.7 cubic yards * 2107 lbs/yd^3 • 66,792 lbs • Rated weight for truck is 82,533 lbs • Because this truck hit the volume limit before the weight it is called Volume limited • I bet you can guess what would happen if we were weight limited

15. Now Back to Matching That Loader • We want to fill 31.7 cubic yards of space with a bucket that can carry 19.4 cubic yards of material • 31.7 / 19.4 = 1.63 passes • This is well under the 3 pass minimum for a well distributed load • This loader is too big for a Cat 769

16. Lets Check Out the 773 46.4 yards (I could check for Weight or volume Limit but I already Know and I have Shown you how To check) 46.4/19.4 = 2.4

17. Running Checks on Other Trucks • Cat 775 54.3 cubic yards 2.8 passes • Cat 777 79.1 yd^3 4.1 passes • Cat 789 158 yd^3 8.1 passes • Now we are getting near an upper practical limit • Obviously the 793 is just too big for our loader • The 789 actually could not turn for single truck loading but we might consider drive by if we wanted it.

18. The integer # of passes problem • 773 was 2.4 passes • 775 was 2.8 passes • 777 was 4.1 passes • 789 was 8.1 passes • None of these are integer numbers • The actual fill can be dictated either by the limits of the material or the need to match the truck • Obviously we need to tweek some fills here to match our truck

19. Adjusted Fill Factors • For 773 46.4/3 = 15.4 cubic yards • 15.4 / 21 = .736 or 73.6% Fill • 85% is about as bad as it gets naturally • The 773 is a bit of a stretch for a match • I’m going to drop it.

20. Continuing Adjustment • 775 54.3 yd^3/ 3 passes • 18.1 yd^3 • 18.1/21 86.2% fill • That’s realistic enough • 3 pass load with 86.2% Fill • 777 79.1 yd^3 in 4 passes with 94% fill – should be doable • 789 158 yd^3 in 8 passes with 94% fill – quite a few passes but for a back hoe loader it might be considered

21. Where Have I Come Out • A Cat 5230 Excavator with a 21 yard bucket • Loading a 775 in 3 passes with Single Truck Loading • Loading a 777 in 4 passes with Single Truck Loading • Loading a 789 in 8 passes with Drive by Loading

22. What Did It Take to Get A Match? • I Needed to find out whether my truck was going to be volume or weight limited for the material • Loader must be able to clear the edge of the truck and hopefully drop on top of a heaped truck • I needed to get a suitable bucket on my loader and determine what a realistic fill factor was for my material

23. Continuing My Efforts • I needed to adjust the fill factors so that I filled my trucks in a suitable integer number of passes.