I don’t really talk about my job much mainly because it’s difficult to explain. A Dentist or Teacher or Author or Pilot is easy to understand because we all have reaped the fruits of their labor at some point in our lives.
But an open pit mine engineer works everyday solving problems that most people have never thought about or just don’t understand. One such problem is ensuring rock walls are safe to work under as the pit gets deeper, say 700 meters deep in some cases.
A pile of sand or gravel has a slope of approximately 35-36 degrees. Broken rock behaves the same way and will often settle at roughly 36 degrees. This number is known as the Angle of Repose.
When developing the walls of an open pit mine, engineers use wall control blasting and proper pit design to make steep walls often times much steeper than the natural angle of repose. Steeper walls mean miners have to remove less overburden (waste) and get to the bottom sooner where the ore is. Achieving an overall angle of just 1 degree steeper can potentially bring forward millions of dollars’ worth of ore. Mining companies pay engineers and consultants to get that one degree.
But steeper is only better to a point where the walls become unsafe to work beneath. Blasting damage, rock structure and faults, or weathering of the walls overtime creates rockfall hazards that could hurt workers or equipment below.
One method of making walls safe that I haven't seen used in the USA but is common here in Australia is manual scaling of walls to remove boulders. I suspect the reason for this is that most mines I have seen in the USA are very shallow because of the highly fractured rock type. Therefore, the walls tend to be only 37-45 degrees versus 55+ degrees in Australia. The risk is much less severe.
Manually scaling of highwalls appears to be a pretty cool job. Guy’s abseil over the walls with crowbars to pry off any dangerous rocks hanging there. Sometimes drilling and blasting is required to remove large rocks. Imagine hanging 300 meters off the ground holding on to a large vibrating drill dodging rocks falling all around you.
So the best job in the world might be this one….Workers are drilling and blasting a rock above the Homer Tunner near the Milford Sound in New Zealand. Watch just to see the epic scenery if for no other reason.