Hydraulic Excavator - Backhoe or Shovel?

Over the last few decades there have been considerable advances in the size of hydraulic excavators available on the market.  Prior to this if you wanted to move very large quantities of material you had to buy something that only came in a shovel configuration and had ropes on it.  The first mine I worked on had lumps of iron weighing over 500 tonnes swinging a monumental 13m3 bucket.  You can achieve the same result today with something that is less than half that size and far more flexible.

There are many factors to consider when selecting a digging tool.  And for hydraulic excavators you need to decide the configuration - backhoe or shovel.  In some regions it is simply a cultural thing.  In fact, some still refer to the larger hydraulic excavators as shovels - have a look at the products list on arguably the two largest mining equipment OEM websites and note what they consider is an excavator versus a mining shovel.

To make it extremely clear - there are many factors to consider.  One more time, there are many factors to consider when deciding on a backhoe or a shovel.  But I want to highlight one in particular that may sometimes be overlooked from an economic perspective.

The prime purpose of a mining excavator is to load dump trucks.  And where those dump trucks are loaded in relation to where they are hauling their material is commonly a large component of the overall economic equation for a mine.  In many mines the truck fleet represents anything from 30% to 50% of the total cost per tonne mined.

Because of their configuration, backhoes will excavate material from flitch heights that are typically 3m to 5m in height.  Shovels on the other hand should typically work on bench heights that are no less than 8m to 10m.

If you consider a typical open pit, that is one where excavation commences at or near average ground levels and continues well below it, the material is excavated and hauled up-hill to its final destination.  In this case the total material tonne-kilometres for the pit excavation will vary depending on whether you are using a backhoe or shovel.  This is because the weighted average level on which the trucks are loaded, and then haul from, will be higher up in the pit with the backhoe compared to the shovel.

Do the math and you will see this, I don't intend to do it here.

Depending on the shape and depth of your pit, and all other things being equal, taking material out in 3m to 5m layers will see your dump trucks doing at least 3% to 5% less tonne-kilometres getting to the pit exit than doing the same with say 10m benches.  That is, your truck fleet will work harder to move the same material under a shovel.

This of course works in reverse if you have a "pit" that is up the side of a hill where most of your haulage is downhill.  Though in this case the economic difference for the truck fleet will be less since there is assistance from a thing called gravity which will lessen the effect on fuel burn.

One other thing.  I have learned from direct experience that if you are considering a hydraulic excavator that has a mass of less than 300 tonnes and you want it in shovel configuration then think again.  The existence of Newton's Third Law means that it will often be resistant to staying at the dig face while it is trying to fill that bucket which is its prime purpose.

Anyway, I hope this helps when in a situation where you are contemplating that important excavator choice of backhoe or shovel, and as always, caveat emptor.