Let’s start with the question – what is an unreliable mine plan? I think the simplest definition of this is a plan that has a short shelf life.  It has a short life before it becomes redundant because the plan is wrong and so therefore needs to be rescheduled.  In previous articles or posts, I have used the terminology “poor plans” instead of unreliable, but I think that terminology was a bit harsh and unfair.

Because let’s be clear here, an unreliable plan is not just a case of poor scheduling work by the mine planner.  There are many other reasons that an execution plan could have a short shelf life, including the following.

   One of the most common reasons is the use of optimistic assumptions. These optimistic assumptions are often not by choice for the planner, as they are told what inputs to use.

·      Beyond input assumptions, management direction can occur in other areas of the plan that are not by the planner’s choice, such as prioritising activities that achieve certain KPI’s.

·      The Production team choosing to not follow the plan, or to not focus on critical issues within the plan that has been communicated to them.

·      Other data sources used in the plan could be inaccurate, such as the geology, or the maintenance planning.

·      Events or delays that can’t be predicted, such as weather.

·      And it could simply be the case that the mine planner has not been given sufficient time to carry out the necessary level of due diligence that they would have wanted to put into the plan.

Since this article is about execution plans, we should define what they are.  Execution plans are those plans which are actually implemented.  I would define an execution plan as any plan from a month down, although realistically it’s more so your weekly and daily plans.  Longer-term plans than this I would describe as decision plans or information plans.  As far as I’m concerned, execution plans are by far the most important plans, far more important than decision or information plans and that is why many of my articles focus on them (although I may have not used that terminology at the time!)

I’ve worked at plenty of mines where execution plans are pretty much taken for granted and not taken seriously.  Site personnel get frustrated about what they describe as poor mine plans, and they live with them, without necessarily thinking about the cost of these execution plans that don’t work. So let’s talk about the costs of an execution plan with a short shelf life.

Firstly, there are the costs that are obvious for all to see. The most obvious of these is equipment idle or downtime, for example, when one item of equipment parks up because a preceding task has not been completed in time.  Another obvious cost is when tasks are forced to be carried out in an inefficient or unproductive manner.  So for example, a drill only works on half of the pattern, because the other half of the bench needs to be left open for trucks to drive through as part of their haul circuit.  Or for a dragline to come back off an extended key pass onto the blocks pass earlier than planned because coal needs to be uncovered, subsequently increasing the dragline rehandle.

Those are two of the obvious costs, but there are hidden costs as well that we don’t necessarily appreciate.  Firstly, there’s the issue of a poor culture that permeates a mine site once mine plans prove themselves to be unreliable. The mine plan becomes undervalued and so it becomes much more common for it to not be followed – which as discussed in my third dot point above, increases the probability of the plan being unreliable. This culture can then also extend into other technical work, such as mine designs being undervalued and not followed. It’s the top of a slippery slope!!

Another cost of unreliable mine plans is the choice to carry higher inventories.  Inventories are needed to cater for the uncertainty in the plan and to ensure that equipment can continue to operate. The lower the confidence in the plan, then the higher the inventories that are carried. These higher inventories are generally in place for every activity in the sequence and so can total to a very high cost across the mine site. 

But there’s something else that we consciously (or subconsciously) build into our plans and we don’t necessarily directly associate it with unreliable execution plans with short shelf lives.  And that is building flexibility into our plans.  I believe that building flexibility into our plans, is something we do to cater for the fact we know the plan is not likely to work.  If there is no flexibility within our plan, when we have a task conflict, such as one task awaiting another, we will have no choice other than for one task to stop and wait for the other.  But flexibility gives us options, it allows us to change the plan every time we get a task conflict.  Flexibility is just a proxy for inaccuracy!

There’s a school of thinking that a good plan has flexibility built-in and that this maximises throughput and minimizes costs.  But I would argue that where flexibility is used to minimizes costs, it minimizes those costs that are readily obvious, such as downtime and unproductive work.  But what is hidden is the cost of having that flexibility in the first place.  Flexibility effectively means that we need more options for mining equipment to move to when the plan doesn’t work.  In open cut mining, ultimately that means we need a bigger void because it means more available face positions, whether it’s for drilling, blasting, or excavation.  Providing a larger void requires a financial investment, in addition to potentially hauling waste further. So costs are increased, but because it’s a hidden cost, we instead take this path of minimizing obvious costs, such as idle equipment.

So, what have I missed? I’m interested to hear of any of the other costs of execution plans with short shelf lives, I would love to see them in the comments.  Next article I’ll try and define these costs in dollars.