Published in the June 2010 Australian Longwall Magazine

AFTER some 36 years in the longwall mining business, I have witnessed the dramatic evolution of mechanisation and the birth and growth of computerisation on longwall equipment.

So just how will the technology evolve in the future? Read on.

The huge advances in technology have provided us with the tools to produce coal in ever-increasing quantities at lower cost and in a safer environment.

However, one thing has remained constant throughout my 36 years in the industry, and that is that roof falls occur for the same reasons as they always did – human error*.

Roof falls still cost the industry hundreds of millions of dollars every year and they expose our workforce to very significant hazards.

To put this into perspective, can you imagine sending a crew of construction workers into a partly demolished building damaged by an earthquake and saying “In you go chaps, just glue it up and away we go”?

Fixing roof falls on a longwall is a bit like that but we are dealing with thousands of tonnes of unstable rocks above our heads that can free fall with enormous energy. Ask anyone who has been in a roof support when the overlying strata fails and the rocks come crashing down; I can tell you from personal experience it is not a good thing.

Unfortunately, we cannot just demolish the longwall and start again. We have to fix it.

The best way to fix roof falls is to stop them from happening in the first place. This is where the future of longwall technology will take us and most of the technology is already available.

First let’s examine the seven deadly longwall sins that most commonly lead to roof failures.If we can eliminate these practices, we will reduce the occurrence of such incidents by 90%. This will also eradicate the need for some longwall consultants.

1. Slothfulness

Operating the longwall with only one pump. This is far more common than you would think and done for no sane reason other than to keep production going. The irony is that such a practice degrades roof support and causes more serious problems. Bring back hanging for this one.

2. Complacency

Operating the longwall supports at less than the designed setting pressures causes the majority of roof failures and should be outlawed.

3. Inactivity

Leaving supports back when they should and can be advanced. Happens on almost every longwall to some extent and is plain crazy. Roof conditions will deteriorate with time. Stopping a longwall is necessary but should be minimal.

4. Lack of discipline

Bends on the longwall? This is a roof fall just waiting to happen. Maybe this should be the number one sin?

5. Mismanagement

Of AFC creep – happening on a longwall near you. AFC creep can be catastrophic. Mismanagement of horizon – get this wrong and everything else has to follow.

6. Excess

Too big a canopy tip to face distance (before cut) significantly increases the risk of failure.

Anything over 600mm is excessive. Anything over 800mm is bad. Anything over 1000mm is very bad.

7. Lack of maintenance

Leaks and bypasses will degrade the effectiveness of roof support. Good maintenance of equipment is directly related to good roof control.

So if the above sins lead to 90% of roof falls, this should give us some clues on the evolution of future longwall technology.

In part two I will give you my vision of how longwall technology will evolve in the next few years.

* Human error can result from the best intentions of a variety of people, including (but not limited to): planners, general managers, accountants, engineers (all disciplines), managers, superintendents, coordinators, supervisors, operators, consultants and OEMs. That should cover it.