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

Backhoes and Excavators l Backhoe is a digging arm and bucket attached to the back of a machine l 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

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

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

The Heap Effect Truck Bed Cross Section 18 ft 2 inches How high is this center 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

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

Fill Factors l 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 l Digging down on an intact face is rather difficult May get about 90 to 95% of rated About 92% is 19.4 cubic yards

Need to Fill in a Reasonable Number of Passes l If you fill a truck with less than 3 passes you can’t get the load distributed – you’ll kill the suspension system l If you take too many passes to fill the truck will spend a large part of its cycle time sitting to be loaded. l 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)

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

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

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

A Material Caution l In place rock is a solid with only internal air spaces and pores l 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

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.

In Our Case We Are Given the Loose Weight l 2107 lbs per cubic yard l 31.7 cubic yards * 2107 lbs/yd^3 66,792 lbs Rated weight for truck is 82,533 lbs l 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

Now Back to Matching That Loader l 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

Lets Check Out the 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

Running Checks on Other Trucks l Cat cubic yards 2.8 passes l Cat yd^3 4.1 passes l Cat 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.

The integer # of passes problem l 773 was 2.4 passes l 775 was 2.8 passes l 777 was 4.1 passes l 789 was 8.1 passes l 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

Adjusted Fill Factors l For /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.

Continuing Adjustment l yd^3/ 3 passes 18.1 yd^3 18.1/ % fill That’s realistic enough 3 pass load with 86.2% Fill l yd^3 in 4 passes with 94% fill – should be doable l yd^3 in 8 passes with 94% fill – quite a few passes but for a back hoe loader it might be considered

Where Have I Come Out l 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

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

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