MINE PLANNING

Planning Process

Once all the exploration information is available, planning can begin in earnest, though often it begins while the exploration process is still in progress.
The start of the planning process is the elimination of any parts of the lease which cannot be worked at all or cannot be readily mined for whatever reason. This, together with some knowledge of coal quality will allow an estimate of the value of the resource, depending on the assumptions made regarding operating costs, the percentage of coal recoverable and future sale prices.
Assuming the project continues past this point, the next step would be to decide seam access locations. This will require an assessment of possible surface sites taking into account all factors as described in the following section "Access to Seam from Surface", and the result will probably entail additional constraints on planned workings.
A decision has to be made on the type of operation – a longwall or continuous miner only operation and production levels desired, which will suggest the type of mine layout and quantity and size of equipment.
At this stage a mine layout has to be designed to fit in with the known constraints, either for the life of the mine or for an acceptable period (5, 10, 20 years, whatever is considered adequate by the mine owners). In order to do this, some strata stability assessments need to be made to ensure whatever pillar size(s) has been chosen is stable and what extent of roof support will be required (primary and secondary). A forecast of likely development and extraction rates will also be required.
Any layout should at least consider the best mining direction with regard to stresses (generally roadways parallel to the major principal stress are most stable), assuming something is known of the stress field. Consideration also needs to be given to seam gradients and any effects these may have on operations; what will happen to mine gases in goaf areas, where will waste water run or accumulate?
The time it will take to travel from surface to the face areas of the mine at different times in the mine life can become an important factor particularly with regard to personnel transport. While people are travelling they are being paid but are not doing productive work – either production stops during the shift change, or shifts overlap so the labour costs effectively double during the shift change (or even treble in the event of overtime being paid during travel time). This can affect the type of seam access chosen and its location.
Having completed a design for the mine (or maybe several alternatives), it will be necessary to see if it works satisfactorily. Initially this would be a physical check to see if, for example, the development units can complete panels in time for longwall continuity, if annual production rates are satisfactory, etc. This can be done manually, measuring on a mine plan where mining units will be periodically, but this is a very time consuming process.
There are now various types of computer program which can be used for planning purposes. These range from standard project management programs where information is in word or numerical form through to programs designed specifically for mining and which can also present information in a pictorial (plan) form.
The ability to ventilate the mine also needs to be checked and again there are computer programs available for this purpose, Ventsim being the most widely used in Australian underground coal mines.
Setting-up computer models and manipulating them is a somewhat specialized skill and, unless training of mine personnel can be justified for this purpose, specialist consultants are generally used.
If starting with a blank sheet, the number of possible variations to a mine design is large, and even with the use of computer models it is not practical to examine all of them. Some parameters will always have to be specified in advance to limit the modeling to be done (eg longwall face length is often specified in advance).
Initially, the model detail need not be great in order to quickly eliminate less successful options, but detail needs to be steadily increased as the best options become more apparent.
Having obtained a small number of likely options, financial details need to be included to evaluate the overall economics of each option. Most computer based mine planning programs are able to undertake basic financial and economic evaluations. Either forecasts have to be made with regard to relative costs and sale prices of the product (including movements in international currency values) or the evaluations are worked out in today's dollar values based on the assumption that relative values remain unchanged. It is possible that financial results may indicate the need for a complete revision of the mine plan at this stage.
Following the above process, possibly for several alternatives, a final optimized plan will emerge. This should be examined for sensitivity to a range of variables so that the key factors likely to affect performance are understood. This is a simple process once the computer model is constructed.
By this stage the degree of detail included in the model should be great. Even apparently small factors can have a major effect. As an example, say a niche to locate equipment has to be mined in each pillar of a longwall panel and each one takes only an hour to excavate and support. It would not be uncommon to have 40-50 pillars in a panel, so the niches amount to around 2 days work assuming 24 hour operations. To have a longwall idle for 2 days can easily amount to $2million or more of lost income, a not inconsiderable amount (it may not be totally lost but will not be recoverable until the end of the mine life which could be too far away to be considered).
It is suggested above that the planning process is a step by step process going from a starting point and progressing steadily to a finished plan. In truth it is more of an iterative process with several possible start points. As plans are developed, better ways of carrying out earlier parts may be identified requiring a reassessment of the plan from that part onwards.
Though the process will arrived at a "final" plan on which the project proceeds, this should be reviewed continually, including updating the latest position of mining units, the latest exploration information and possibly including adjusted production or development rates and costs/prices based on actual performance or revised forecasts. This ongoing planning process can be equally as important to a mine's success as the initial plan prior to the start.